WebGPU

1. Introduction

This section is non-normative.

Graphics Processing Units, or GPUs for short, have been essential in enabling rich rendering and computational applications in personal computing. WebGPU is an API that exposes the capabilities of GPU hardware for the Web. The API is designed from the ground up to efficiently map to the Vulkan, Direct3D 12, and Metal native GPU APIs. WebGPU is not related to WebGL and does not explicitly target OpenGL ES.

WebGPU sees physical GPU hardware as GPUAdapters. It provides a connection to an adapter via GPUDevice, which manages resources, and the device’s GPUQueues, which execute commands. GPUDevice may have its own memory with high-speed access to the processing units. GPUBuffer and GPUTexture are the physical resources backed by GPU memory. GPUCommandBuffer and GPURenderBundle are containers for user-recorded commands. GPUShaderModule contains shader code. The other resources, such as GPUSampler or GPUBindGroup, configure the way physical resources are used by the GPU.

GPUs execute commands encoded in GPUCommandBuffers by feeding data through a pipeline, which is a mix of fixed-function and programmable stages. Programmable stages execute shaders, which are special programs designed to run on GPU hardware. Most of the state of a pipeline is defined by a GPURenderPipeline or a GPUComputePipeline object. The state not included in these pipeline objects is set during encoding with commands, such as beginRenderPass() or setBlendColor().

2. Malicious use considerations

This section is non-normative. It describes the risks associated with exposing this API on the Web.

2.1. Security

The security requirements for WebGPU are the same as ever for the web, and are likewise non-negotiable. The general approach is strictly validating all the commands before they reach GPU, ensuring that a page can only work with its own data.

2.1.1. CPU-based undefined behavior

A WebGPU implementation translates the workloads issued by the user into API commands specific to the target platform. Native APIs specify the valid usage for the commands (for example, see vkCreateDescriptorSetLayout) and generally don’t guarantee any outcome if the valid usage rules are not followed. This is called "undefined behavior", and it can be exploited by an attacker to access memory they don’t own, or force the driver to execute arbitrary code.

In order to disallow insecure usage, the range of allowed WebGPU behaviors is defined for any input. An implementation has to validate all the input from the user and only reach the driver with the valid workloads. This document specifies all the error conditions and handling semantics. For example, specifying the same buffer with intersecting ranges in both "source" and "destination" of copyBufferToBuffer() results in GPUCommandEncoder generating an error, and no other operation occurring.

See § 20 Errors & Debugging for more information about error handling.

2.2. GPU-based undefined behavior

WebGPU shaders are executed by the compute units inside GPU hardware. In native APIs, some of the shader instructions may result in undefined behavior on the GPU. In order to address that, the shader instruction set and its defined behaviors are strictly defined by WebGPU. When a shader is provided to createShaderModule(), the WebGPU implementation has to validate it before doing any translation (to platform-specific shaders) or transformation passes.

2.3. Uninitialized data

Generally, allocating new memory may expose the leftover data of other applications running on the system. In order to address that, WebGPU conceptually initializes all the resources to zero, although in practice an implementation may skip this step if it sees the developer initializing the contents manually. This includes variables and shared workgroup memory inside shaders.

The precise mechanism of clearing the workgroup memory can differ between platforms. If the native API does not provide facilities to clear it, the WebGPU implementation transforms the compute shader to first do a clear across all invocations, synchronize them, and continue executing developer’s code.

2.4. Out-of-bounds access in shaders

Shaders can access physical resources either directly (for example, as a "uniform" GPUBufferBinding), or via texture units, which are fixed-function hardware blocks that handle texture coordinate conversions. Validation on the API side can only guarantee that all the inputs to the shader are provided and they have the correct usage and types. The host API side can not guarantee that the data is accessed within bounds if the texture units are not involved.

define the host API distinct from the shader API

In order to prevent the shaders from accessing GPU memory an application doesn’t own, the WebGPU implementation may enable a special mode (called "robust buffer access") in the driver that guarantees that the access is limited to buffer bounds.

Alternatively, an implementation may transform the shader code by inserting manual bounds checks. When this path is taken, the out-of-bound checks only apply to array indexing. They aren’t needed for plain field access of shader structures due to the minBindingSize validation on the host side.

If the shader attempts to load data outside of physical resource bounds, the implementation is allowed to:

1. return a value at a different location within the resource bounds

2. return a value vector of "(0, 0, 0, X)" with any "X"

3. partially discard the draw or dispatch call

If the shader attempts to write data outside of physical resource bounds, the implementation is allowed to:

1. write the value to a different location within the resource bounds

2. discard the write operation

3. partially discard the draw or dispatch call

2.5. Invalid data

When uploading floating-point data from CPU to GPU, or generating it on the GPU, we may end up with a binary representation that doesn’t correspond to a valid number, such as infinity or NaN (not-a-number). The GPU behavior in this case is subject to the accuracy of the GPU hardware implementation of the IEEE-754 standard. WebGPU guarantees that introducing invalid floating-point numbers would only affect the results of arithmetic computations and will not have other side effects.

2.5.1. Driver bugs

GPU drivers are subject to bugs like any other software. If a bug occurs, an attacker could possibly exploit the incorrect behavior of the driver to get access to unprivileged data. In order to reduce the risk, the WebGPU working group will coordinate with GPU vendors to integrate the WebGPU Conformance Test Suite (CTS) as part of their driver testing process, like it was done for WebGL. WebGPU implementations are expected to have workarounds for some of the discovered bugs, and disable WebGPU on drivers with known bugs that can’t be worked around.

2.5.2. Timing attacks

WebGPU is designed for multi-threaded use via Web Workers. As such, it is designed not to open the users to modern high-precision timing attacks. Some of the objects, like GPUBuffer or GPUQueue, have shared state which can be simultaneously accessed. This allows race conditions to occur, similar to those of accessing a SharedArrayBuffer from multiple Web Workers, which makes the thread scheduling observable.

WebGPU addresses this by limiting the ability to deserialize (or share) objects only to the agents inside the agent cluster, and only if the cross-origin isolated policies are in place. This restriction matches the mitigations against the malicious SharedArrayBuffer use. Similarly, the user agent may also serialize the agents sharing any handles to prevent any concurrency entirely.

In the end, the attack surface for races on shared state in WebGPU will be a small subset of the SharedArrayBuffer attacks.

WebGPU also specifies the "timestamp-query" feature, which provides high precision timing of GPU operations. The feature is optional, and a WebGPU implementation may limit its exposure only to those scenarios that are trusted. Alternatively, the timing query results could be processed by a compute shader and aligned to a lower precision.

2.5.3. Row hammer attacks

Row hammer is a class of attacks that exploit the leaking of states in DRAM cells. It could be used on GPU. WebGPU does not have any specific mitigations in place, and relies on platform-level solutions, such as reduced memory refresh intervals.

2.6. Denial of service

WebGPU applications have access to GPU memory and compute units. A WebGPU implementation may limit the available GPU memory to an application, in order to keep other applications responsive. For GPU processing time, a WebGPU implementation may set up "watchdog" timer that makes sure an application doesn’t cause GPU unresponsiveness for more than a few seconds. These measures are similar to those used in WebGL.

2.7. Workload identification

WebGPU provides access to constrained global resources shared between different programs (and web pages) running on the same machine. An application can try to indirectly probe how constrained these global resources are, in order to reason about workloads performed by other open web pages, based on the patterns of usage of these shared resources. These issues are generally analogous to issues with Javascript, such as system memory and CPU execution throughput. WebGPU does not provide any additional mitigations for this.

2.7.1. Memory resources

WebGPU exposes fallible allocations from machine-global memory heaps, such as VRAM. This allows for probing the size of the system’s remaining available memory (for a given heap type) by attempting to allocate and watching for allocation failures.

GPUs internally have one or more (typically only two) heaps of memory shared by all running applications. When a heap is depleted, WebGPU would fail to create a resource. This is observable, which may allow a malicious application to guess what heaps are used by other applications, and how much they allocate from them.

2.7.2. Computation resources

If one site uses WebGPU at the same time as another, it may observe the increase in time it takes to process some work. For example, if a site constantly submits compute workloads and tracks completion of work on the queue, it may observe that something else also started using the GPU.

A GPU has many parts that can be tested independently, such as the arithmetic units, texture sampling units, atomic units, etc. A malicious application may sense when some of these units are stressed, and attempt to guess the workload of another application by analyzing the stress patterns. This is analogous to the realities of CPU execution of Javascript.

2.8. Privacy

2.8.1. Machine-specific limits

WebGPU can expose a lot of detail on the underlying GPU architecture and the device geometry. This includes available physical adapters, many limits on the GPU and CPU resources that could be used (such as the maximum texture size), and any optional hardware-specific capabilities that are available.

User agents are not obligated to expose the real hardware limits, they are in full contol of how much the machine specifics are exposed. One strategy to reduce fingeprinting is binning all the target platforms into a few number of bins. In general, the privacy impact of exposing the hardware limits matches the one of WebGL.

The baseline (guaranteed) limits are also deliberately high enough to allow most application to work without requesting higher limits. All the usage of the API is validated according to the requested limits, so the actual hardware capabilities are not exposed to the users by accident.

2.8.2. Machine-specific artifacts

There are some machine-specific rasterization/precision artifacts and performance differences that can be observed roughly in the same way as in WebGL. This applies to rasterization coverage and patterns, interpolation precision of the varyings between shader stages, compute unit scheduling, and more aspects of execution.

Generally, rasterization and precision fingerprints are identical across most or all of the devices of each vendor. Performance differences are relatively intractable, but also relatively low-signal (as with JS execution performance).

Privacy-critical applications and user agents should utilize software implementations to eliminate such artifacts.

2.8.3. Machine-specific performance

Another factor for differentiating users is measuring the performance of specific operations on the GPU. Even with low precision timing, repeated execution of an operation can show if the user’s machine is fast at specific workloads. This is a fairly common vector (present in both WebGL and Javascript), but it’s also low-signal and relatively intractable to truly normalize.

WebGPU compute pipelines expose access to GPU unobstructed by the fixed-function hardware. This poses an additional risk for unique device fingerprinting. User agents can take steps to dissociate logical GPU invocations with actual compute units to reduce this risk.

3. Fundamentals

3.1. Conventions

3.1.1. Dot Syntax

In this specification, the . ("dot") syntax, common in programming languages, is used. The phrasing "Foo.Bar" means "the Bar member of the value (or interface) Foo."

For example, where buffer is a GPUBuffer, buffer.[[device]].[[adapter]] means "the [[adapter]] internal slot of the [[device]] internal slot of buffer.

3.1.2. Internal Objects

An internal object is a conceptual, non-exposed WebGPU object. Internal objects track the state of an API object and hold any underlying implementation. If the state of a particular internal object can change in parallel from multiple agents, those changes are always atomic with respect to all agents.

Note: An "agent" refers to a JavaScript "thread" (i.e. main thread, or Web Worker).

3.1.3. WebGPU Interfaces

A WebGPU interface is an exposed interface which encapsulates an internal object. It provides the interface through which the internal object's state is changed.

As a matter of convention, if a WebGPU interface is referred to as invalid, it means that the internal object it encapsulates is invalid.

Any interface which includes GPUObjectBase is a WebGPU interface.

interface mixin GPUObjectBase {
    attribute USVString? label;
};

GPUObjectBase has the following attributes:

label, of type USVString, nullable

A label which can be used by development tools (such as error/warning messages, browser developer tools, or platform debugging utilities) to identify the underlying internal object to the developer. It has no specified format, and therefore cannot be reliably machine-parsed.

In any given situation, the user agent may or may not choose to use this label.

GPUObjectBase has the following internal slots:

[[device]], of type device, readonly

An internal slot holding the device which owns the internal object.

3.1.4. Object Descriptors

An object descriptor holds the information needed to create an object, which is typically done via one of the create* methods of GPUDevice.

dictionary GPUObjectDescriptorBase {
    USVString label;
};

GPUObjectDescriptorBase has the following members:

label, of type USVString

The initial value of GPUObjectBase.label.

3.2. Invalid Internal Objects & Contagious Invalidity

If an object is successfully created, it is valid at that moment. An internal object may be invalid. It may become invalid during its lifetime, but it will never become valid again.

3.3. Coordinate Systems

WebGPU’s coordinate systems match DirectX and Metal’s coordinate systems in a graphics pipeline.

• Y-axis is up in normalized device coordinate (NDC): point(-1.0, -1.0) in NDC is located at the bottom-left corner of NDC. In addition, x and y in NDC should be between -1.0 and 1.0 inclusive, while z in NDC should be between 0.0 and 1.0 inclusive. Vertices out of this range in NDC will not introduce any errors, but they will be clipped.

• Y-axis is down in framebuffer coordinate, viewport coordinate and fragment/pixel coordinate: origin(0, 0) is located at the top-left corner in these coordinate systems.

• Window/present coordinate matches framebuffer coordinate.

• UV of origin(0, 0) in texture coordinate represents the first texel (the lowest byte) in texture memory.

3.4. Programming Model

3.4.1. Timelines

This section is non-normative.

A computer system with a user agent at the front-end and GPU at the back-end has components working on different timelines in parallel:

Content timeline

Associated with the execution of the Web script. It includes calling all methods described by this specification.

Steps executed on the content timeline look like this.

Device timeline

Associated with the GPU device operations that are issued by the user agent. It includes creation of adapters, devices, and GPU resources and state objects, which are typically synchronous operations from the point of view of the user agent part that controls the GPU, but can live in a separate OS process.

Steps executed on the device timeline look like this.

Queue timeline

Associated with the execution of operations on the compute units of the GPU. It includes actual draw, copy, and compute jobs that run on the GPU.

Steps executed on the queue timeline look like this.

In this specification, asynchronous operations are used when the result value depends on work that happens on any timeline other than the Content timeline. They are represented by callbacks and promises in JavaScript.

3.4.2. Memory Model

This section is non-normative.

Once a GPUDevice has been obtained during an application initialization routine, we can describe the WebGPU platform as consisting of the following layers:

1. User agent implementing the specification.

2. Operating system with low-level native API drivers for this device.

3. Actual CPU and GPU hardware.

Each layer of the WebGPU platform may have different memory types that the user agent needs to consider when implementing the specification:

• The script-owned memory, such as an ArrayBuffer created by the script, is generally not accessible by a GPU driver.

• A user agent may have different processes responsible for running the content and communication to the GPU driver. In this case, it uses inter-process shared memory to transfer data.

• Dedicated GPUs have their own memory with high bandwidth, while integrated GPUs typically share memory with the system.

Most physical resources are allocated in the memory of type that is efficient for computation or rendering by the GPU. When the user needs to provide new data to the GPU, the data may first need to cross the process boundary in order to reach the user agent part that communicates with the GPU driver. Then it may need to be made visible to the driver, which sometimes requires a copy into driver-allocated staging memory. Finally, it may need to be transferred to the dedicated GPU memory, potentially changing the internal layout into one that is most efficient for GPUs to operate on.

All of these transitions are done by the WebGPU implementation of the user agent.

Note: This example describes the worst case, while in practice the implementation may not need to cross the process boundary, or may be able to expose the driver-managed memory directly to the user behind an ArrayBuffer, thus avoiding any data copies.

3.4.3. Multi-Threading

3.4.4. Resource Usages

A physical resource can be used on GPU with an internal usage:

input

Buffer with input data for draw or dispatch calls. Preserves the contents. Allowed by buffer INDEX, buffer VERTEX, or buffer INDIRECT.

constant

Resource bindings that are constant from the shader point of view. Preserves the contents. Allowed by buffer UNIFORM or texture SAMPLED.

storage

Read-write storage resource binding. Allowed by buffer STORAGE.

storage-read

Read-only storage resource bindings. Preserves the contents. Allowed by buffer STORAGE or texture STORAGE.

storage-write

Write-only storage resource bindings. Allowed by texture STORAGE.

attachment

Texture used as an output attachment in a render pass. Allowed by texture RENDER_ATTACHMENT.

attachment-read

Texture used as a read-only attachment in a render pass. Preserves the contents. Allowed by texture RENDER_ATTACHMENT.

Textures may consist of separate mipmap levels and array layers, which can be used differently at any given time. Each such texture subresource is uniquely identified by a texture, mipmap level, and (for 2d textures only) array layer, and aspect.

We define subresource to be either a whole buffer, or a texture subresource.

Enforcing that the usages are only combined into a compatible usage list allows the API to limit when data races can occur in working with memory. That property makes applications written against WebGPU more likely to run without modification on different platforms.

Generally, when an implementation processes an operation that uses a subresource in a different way than its current usage allows, it schedules a transition of the resource into the new state. In some cases, like within an open GPURenderPassEncoder, such a transition is impossible due to the hardware limitations. We define these places as usage scopes.

The main usage rule is, for any one subresource, its list of internal usages within one usage scope must be a compatible usage list.

For example, binding the same buffer for storage as well as for input within the same GPURenderPassEncoder would put the encoder as well as the owning GPUCommandEncoder into the error state. This combination of usages does not make a compatible usage list.

Note: race condition of multiple writable storage buffer/texture usages in a single usage scope is allowed.

The subresources of textures included in the views provided to GPURenderPassColorAttachmentDescriptor.attachment and GPURenderPassColorAttachmentDescriptor.resolveTarget are considered to be used as attachment for the usage scope of this render pass.

The physical size of a texture subresource is the dimension of the texture subresource in texels that includes the possible extra paddings to form complete texel blocks in the subresource.

• For pixel-based GPUTextureFormats, the physical size is always equal to the size of the texture subresource used in the sampling hardwares.

• Textures in block-based compressed GPUTextureFormats always have a mipmap level 0 whose [[textureSize]] is a multiple of the texel block size, but the lower mipmap levels might not be the multiple of the texel block size and can have paddings.

3.4.5. Synchronization

For each subresource of a physical resource, its set of internal usage flags is tracked on the Queue timeline.

This section will need to be revised to support multiple queues.

On the Queue timeline, there is an ordered sequence of usage scopes. Each item on the timeline is contained within exactly one scope. For the duration of each scope, the set of internal usage flags of any given subresource is constant. A subresource may transition to new usages at the boundaries between usage scopes.

This specification defines the following usage scopes:

1. an individual command on a GPUCommandEncoder, such as GPUCommandEncoder.copyBufferToTexture.

2. an individual command on a GPUComputePassEncoder, such as GPUProgrammablePassEncoder.setBindGroup.

3. the whole GPURenderPassEncoder.

The usage scopes are validated at GPUCommandEncoder.finish time. The implementation performs the usage scope validation by composing the list of all internal usage flags of each subresource used in the usage scope. A GPUValidationError is generated in the current scope with an appropriate error message if that list is not a compatible usage list.

3.5. Core Internal Objects

3.5.1. Adapters

An adapter represents an implementation of WebGPU on the system. Each adapter identifies both an instance of a hardware accelerator (e.g. GPU or CPU) and an instance of a browser’s implementation of WebGPU on top of that accelerator.

If an adapter becomes unavailable, it becomes invalid. Once invalid, it never becomes valid again. Any devices on the adapter, and internal objects owned by those devices, also become invalid.

Note: An adapter may be a physical display adapter (GPU), but it could also be a software renderer. A returned adapter could refer to different physical adapters, or to different browser codepaths or system drivers on the same physical adapters. Applications can hold onto multiple adapters at once (via GPUAdapter) (even if some are invalid), and two of these could refer to different instances of the same physical configuration (e.g. if the GPU was reset or disconnected and reconnected).

An adapter has the following internal slots:

[[features]], of type list<GPUFeatureName>, readonly

The features which can be used to create devices on this adapter.

[[limits]], of type GPULimits, readonly

The best limits which can be used to create devices on this adapter.

Each adapter limit must be the same or better than its default value in GPULimits.

Adapters are exposed via GPUAdapter.

3.5.2. Devices

A device is the logical instantiation of an adapter, through which internal objects are created. It can be shared across multiple agents (e.g. dedicated workers).

A device is the exclusive owner of all internal objects created from it: when the device is lost, it and all objects created on it (directly, e.g. createTexture(), or indirectly, e.g. createView()) become invalid.

Define "ownership".

A device has the following internal slots:

[[adapter]], of type adapter, readonly

The adapter from which this device was created.

[[features]], of type list<GPUFeatureName>, readonly

The features which can be used on this device. No additional features can be used, even if the underlying adapter can support them.

[[limits]], of type GPULimits, readonly

The limits which can be used on this device. No better limits can be used, even if the underlying adapter can support them.

Devices are exposed via GPUDevice.

3.6. Optional Capabilities

WebGPU adapters and devices have capabilities, which describe WebGPU functionality that differs between different implementations, typically due to hardware or system software constraints. A capability is either a feature or a limit.

3.6.1. Features

A feature is a set of optional WebGPU functionality that is not supported on all implementations, typically due to hardware or system software constraints.

Each GPUAdapter exposes a set of available features. Only those features may be requested in requestDevice().

Functionality that is part of an feature may only be used if the feature was requested at device creation. See the Feature Index for a description of the functionality each feature enables.

3.6.2. Limits

Each limit is a numeric limit on the usage of WebGPU on a device. Each adapter has a set of supported limits, and devices are created with specific limits in place. The device limits are enforced regardless of the adapter’s limits.

One limit value may be better than another. A better limit value always relaxes validation, enabling strictly more programs to be valid. For each limit, "better" is defined.

Note: Setting "better" limits may not necessarily be desirable, as they may have a performance impact. Because of this, and to improve portability across devices and implementations, applications should generally request the "worst" limits that work for their content (ideally, the default values).

Each limit also has a baseline value. Every adapter is guaranteed to support the baseline value or better. The baseline value is also the default value for the limit in GPULimits if a better limit is not specified.

3.6.2.1. GPULimits

GPULimits describes the limits with which a device should be created. See GPUDeviceDescriptor.limits.

dictionary GPULimits {
    GPUSize32 maxBindGroups = 4;
    GPUSize32 maxDynamicUniformBuffersPerPipelineLayout = 8;
    GPUSize32 maxDynamicStorageBuffersPerPipelineLayout = 4;
    GPUSize32 maxSampledTexturesPerShaderStage = 16;
    GPUSize32 maxSamplersPerShaderStage = 16;
    GPUSize32 maxStorageBuffersPerShaderStage = 4;
    GPUSize32 maxStorageTexturesPerShaderStage = 4;
    GPUSize32 maxUniformBuffersPerShaderStage = 12;
    GPUSize32 maxUniformBufferBindingSize = 16384;
    GPUSize32 maxStorageBufferBindingSize = 134217728;
    GPUSize32 maxVertexBuffers = 8;
    GPUSize32 maxVertexAttributes = 16;
    GPUSize32 maxVertexArrayStride = 2048;
};

3.6.2.2. GPUAdapterFeatures

GPUAdapterFeatures is a setlike interface. Its set entries are the GPUFeatureName values of the features supported by an adapter.

interface GPUAdapterFeatures {
    readonly setlike<GPUFeatureName>;
};

4. Initialization

4.1. Examples

Need a robust example like the one in ErrorHandling.md, which handles all situations. Possibly also include a simple example with no handling.

4.2. navigator.gpu

A GPU object is available via navigator.gpu on the Window:

[Exposed=Window]
partial interface Navigator {
    [SameObject] readonly attribute GPU gpu;
};

... as well as on dedicated workers:

[Exposed=DedicatedWorker]
partial interface WorkerNavigator {
    [SameObject] readonly attribute GPU gpu;
};

4.3. GPU

GPU is the entry point to WebGPU.

[Exposed=(Window, DedicatedWorker)]
interface GPU {
    Promise<GPUAdapter?> requestAdapter(optional GPURequestAdapterOptions options = {});
};

GPU has the following methods:

requestAdapter(options)

Requests an adapter from the user agent. The user agent chooses whether to return an adapter, and, if so, chooses according to the provided options.

Called on: GPU this.

Arguments:

Arguments for the GPU.requestAdapter(options) method.

Parameter	Type	Nullable	Optional	Description
options	GPURequestAdapterOptions	✘	✔	Criteria used to select the adapter.

Returns: Promise<GPUAdapter?>

1. Let promise be a new promise.

2. Issue the following steps on the Device timeline of this:

   1. If the user agent chooses to return an adapter:

      1. The user agent chooses an adapter adapter according to the rules in § 4.3.1 Adapter Selection and the criteria in options.

      2. promise resolves with a new GPUAdapter encapsulating adapter.

   2. Otherwise, promise resolves with null.

3. Return promise.

4.3.1. Adapter Selection

GPURequestAdapterOptions provides hints to the user agent indicating what configuration is suitable for the application.

dictionary GPURequestAdapterOptions {
    GPUPowerPreference powerPreference;
};

enum GPUPowerPreference {
    "low-power",
    "high-performance"
};

GPURequestAdapterOptions has the following members:

powerPreference, of type GPUPowerPreference

Optionally provides a hint indicating what class of adapter should be selected from the system’s available adapters.

The value of this hint may influence which adapter is chosen, but it must not influence whether an adapter is returned or not.

Note: The primary utility of this hint is to influence which GPU is used in a multi-GPU system. For instance, some laptops have a low-power integrated GPU and a high-performance discrete GPU.

Note: Depending on the exact hardware configuration, such as battery status and attached displays or removable GPUs, the user agent may select different adapters given the same power preference. Typically, given the same hardware configuration and state and powerPreference, the user agent is likely to select the same adapter.

It must be one of the following values:

undefined (or not present)

Provides no hint to the user agent.

"low-power"

Indicates a request to prioritize power savings over performance.

Note: Generally, content should use this if it is unlikely to be constrained by drawing performance; for example, if it renders only one frame per second, draws only relatively simple geometry with simple shaders, or uses a small HTML canvas element. Developers are encouraged to use this value if their content allows, since it may significantly improve battery life on portable devices.

"high-performance"

Indicates a request to prioritize performance over power consumption.

Note: By choosing this value, developers should be aware that, for devices created on the resulting adapter, user agents are more likely to force device loss, in order to save power by switching to a lower-power adapter. Developers are encouraged to only specify this value if they believe it is absolutely necessary, since it may significantly decrease battery life on portable devices.

4.4. GPUAdapter

A GPUAdapter encapsulates an adapter, and describes its capabilities (features and limits).

To get a GPUAdapter, use requestAdapter().

interface GPUAdapter {
    readonly attribute DOMString name;
    [SameObject] readonly attribute GPUAdapterFeatures features;
    //readonly attribute GPULimits limits; Don’t expose higher limits for now.

    Promise<GPUDevice?> requestDevice(optional GPUDeviceDescriptor descriptor = {});
};

GPUAdapter has the following attributes:

name, of type DOMString, readonly

A human-readable name identifying the adapter. The contents are implementation-defined.

features, of type GPUAdapterFeatures, readonly

Accessor for this.[[adapter]].[[features]].

GPUAdapter has the following internal slots:

[[adapter]], of type adapter, readonly

The adapter to which this GPUAdapter refers.

GPUAdapter has the following methods:

requestDevice(descriptor)

Requests a device from the adapter.

Called on: GPUAdapter this.

Arguments:

Arguments for the GPUAdapter.requestDevice(descriptor) method.

Parameter	Type	Nullable	Optional	Description
descriptor	GPUDeviceDescriptor	✘	✔	Description of the GPUDevice to request.

Returns: Promise<GPUDevice?>

1. Let promise be a new promise.

2. Issue the following steps to the Device timeline:

   1. If any of the following conditions are unsatisfied, reject promise with an OperationError and stop.

      • The set of GPUFeatureName values in descriptor.features is a subset of those in adapter.[[features]].

      • For each type of limit in GPULimits, the value of that limit in descriptor.limits is no better than the value of that limit in adapter.[[limits]].

      where adapter is this.[[adapter]].

   2. If the user agent cannot fulfill the request, resolve promise to null and stop.

   3. Resolve promise to a new GPUDevice object encapsulating a new device with the capabilities described by descriptor.

3. Return promise.

4.4.1. GPUDeviceDescriptor

GPUDeviceDescriptor describes a device request.

dictionary GPUDeviceDescriptor : GPUObjectDescriptorBase {
    sequence<GPUFeatureName> features = [];
    GPULimits limits = {};
};

GPUDeviceDescriptor has the following members:

features, of type sequence<GPUFeatureName>, defaulting to []

The set of GPUFeatureName values in this sequence defines the exact set of features that must be enabled on the device.

limits, of type GPULimits, defaulting to {}

Defines the exact limits that must be enabled on the device.

4.4.1.1. GPUFeatureName

Each GPUFeatureName identifies a set of functionality which, if available, allows additional usages of WebGPU that would have otherwise been invalid.

enum GPUFeatureName {
    "depth-clamping",
    "depth24unorm-stencil8",
    "depth32float-stencil8",
    "pipeline-statistics-query",
    "texture-compression-bc",
    "timestamp-query",
};

4.5. GPUDevice

A GPUDevice encapsulates a device and exposes the functionality of that device.

GPUDevice is the top-level interface through which WebGPU interfaces are created.

To get a GPUDevice, use requestDevice().

[Exposed=(Window, DedicatedWorker), Serializable]
interface GPUDevice : EventTarget {
    [SameObject] readonly attribute GPUAdapter adapter;
    readonly attribute FrozenArray<GPUFeatureName> features;
    readonly attribute object limits;

    [SameObject] readonly attribute GPUQueue defaultQueue;

    GPUBuffer createBuffer(GPUBufferDescriptor descriptor);
    GPUTexture createTexture(GPUTextureDescriptor descriptor);
    GPUSampler createSampler(optional GPUSamplerDescriptor descriptor = {});

    GPUBindGroupLayout createBindGroupLayout(GPUBindGroupLayoutDescriptor descriptor);
    GPUPipelineLayout createPipelineLayout(GPUPipelineLayoutDescriptor descriptor);
    GPUBindGroup createBindGroup(GPUBindGroupDescriptor descriptor);

    GPUShaderModule createShaderModule(GPUShaderModuleDescriptor descriptor);
    GPUComputePipeline createComputePipeline(GPUComputePipelineDescriptor descriptor);
    GPURenderPipeline createRenderPipeline(GPURenderPipelineDescriptor descriptor);
    Promise<GPUComputePipeline> createReadyComputePipeline(GPUComputePipelineDescriptor descriptor);
    Promise<GPURenderPipeline> createReadyRenderPipeline(GPURenderPipelineDescriptor descriptor);

    GPUCommandEncoder createCommandEncoder(optional GPUCommandEncoderDescriptor descriptor = {});
    GPURenderBundleEncoder createRenderBundleEncoder(GPURenderBundleEncoderDescriptor descriptor);

    GPUQuerySet createQuerySet(GPUQuerySetDescriptor descriptor);
};
GPUDevice includes GPUObjectBase;

GPUDevice has the following attributes:

adapter, of type GPUAdapter, readonly

The GPUAdapter from which this device was created.

features, of type FrozenArray<GPUFeatureName>, readonly

A sequence containing the GPUFeatureName values of the features supported by the device (i.e. the ones with which it was created).

limits, of type object, readonly

A GPULimits object exposing the limits supported by the device (i.e. the ones with which it was created).

defaultQueue, of type GPUQueue, readonly

The default GPUQueue for this device.

GPUDevice has the following internal slots:

[[device]], of type device, readonly

The device that this GPUDevice refers to.

GPUDevice has the methods listed in its WebIDL definition above, which are defined elsewhere in this document.

GPUDevice objects are serializable objects.

GPUDevice doesn’t really need the cross-origin policy restriction. It should be usable from multiple agents regardless. Once we describe the serialization of buffers, textures, and queues - the COOP+COEP logic should be moved in there.

5. Buffers

5.1. GPUBuffer

define buffer (internal object)

A GPUBuffer represents a block of memory that can be used in GPU operations. Data is stored in linear layout, meaning that each byte of the allocation can be addressed by its offset from the start of the GPUBuffer, subject to alignment restrictions depending on the operation. Some GPUBuffers can be mapped which makes the block of memory accessible via an ArrayBuffer called its mapping.

GPUBuffers are created via GPUDevice.createBuffer(descriptor) that returns a new buffer in the mapped or unmapped state.

[Serializable]
interface GPUBuffer {
    Promise<undefined> mapAsync(GPUMapModeFlags mode, optional GPUSize64 offset = 0, optional GPUSize64 size);
    ArrayBuffer getMappedRange(optional GPUSize64 offset = 0, optional GPUSize64 size);
    undefined unmap();

    undefined destroy();
};
GPUBuffer includes GPUObjectBase;

GPUBuffer has the following internal slots:

[[size]] of type GPUSize64.

The length of the GPUBuffer allocation in bytes.

[[usage]] of type GPUBufferUsageFlags.

The allowed usages for this GPUBuffer.

[[state]] of type buffer state.

The current state of the GPUBuffer.

[[mapping]] of type ArrayBuffer or Promise or null.

The mapping for this GPUBuffer. The ArrayBuffer isn’t directly accessible and is instead accessed through views into it, called the mapped ranges, that are stored in [[mapped_ranges]]

Specify [[mapping]] in term of DataBlock similarly to AllocateArrayBuffer? <https://github.com/gpuweb/gpuweb/issues/605>

[[mapping_range]] of type list<Number> or null.

The range of this GPUBuffer that is mapped.

[[mapped_ranges]] of type list<ArrayBuffer> or null.

The ArrayBuffers returned via getMappedRange to the application. They are tracked so they can be detached when unmap is called.

[[map_mode]] of type GPUMapModeFlags.

The GPUMapModeFlags of the last call to mapAsync() (if any).

[[usage]] is differently named from [[textureUsage]]. We should make it consistent.

Each GPUBuffer has a current buffer state on the Content timeline which is one of the following:

• "mapped" where the GPUBuffer is available for CPU operations on its content.

• "mapped at creation" where the GPUBuffer was just created and is available for CPU operations on its content.

• "mapping pending" where the GPUBuffer is being made available for CPU operations on its content.

• "unmapped" where the GPUBuffer is available for GPU operations.

• "destroyed" where the GPUBuffer is no longer available for any operations except destroy.

Note: [[size]] and [[usage]] are immutable once the GPUBuffer has been created.

GPUBuffer is Serializable. It is a reference to an internal buffer object, and Serializable means that the reference can be copied between realms (threads/workers), allowing multiple realms to access it concurrently. Since GPUBuffer has internal state (mapped, destroyed), that state is internally-synchronized - these state changes occur atomically across realms.

5.2. Buffer Creation

5.2.1. GPUBufferDescriptor

This specifies the options to use in creating a GPUBuffer.

dictionary GPUBufferDescriptor : GPUObjectDescriptorBase {
    required GPUSize64 size;
    required GPUBufferUsageFlags usage;
    boolean mappedAtCreation = false;
};

5.3. Buffer Usage

typedef [EnforceRange] unsigned long GPUBufferUsageFlags;
interface GPUBufferUsage {
    const GPUFlagsConstant MAP_READ      = 0x0001;
    const GPUFlagsConstant MAP_WRITE     = 0x0002;
    const GPUFlagsConstant COPY_SRC      = 0x0004;
    const GPUFlagsConstant COPY_DST      = 0x0008;
    const GPUFlagsConstant INDEX         = 0x0010;
    const GPUFlagsConstant VERTEX        = 0x0020;
    const GPUFlagsConstant UNIFORM       = 0x0040;
    const GPUFlagsConstant STORAGE       = 0x0080;
    const GPUFlagsConstant INDIRECT      = 0x0100;
    const GPUFlagsConstant QUERY_RESOLVE = 0x0200;
};

createBuffer(descriptor)

Creates a GPUBuffer.

Called on: GPUDevice this.

Arguments:

Arguments for the GPUDevice.createBuffer(descriptor) method.

Parameter	Type	Nullable	Optional	Description
descriptor	GPUBufferDescriptor	✘	✘	Description of the GPUBuffer to create.

Returns: GPUBuffer

1. If any of the following conditions are unsatisfied, return an error buffer and stop.

   • this is a valid GPUDevice.

   • descriptor.usage is a subset of this.[[allowed buffer usages]].

   • If descriptor.usage contains MAP_READ:

     • descriptor.usage contains no other flags except COPY_DST.

   • If descriptor.usage contains MAP_WRITE:

     • descriptor.usage contains no other flags except COPY_SRC.

   • If descriptor.mappedAtCreation is true:

     • descriptor.size is a multiple of 4.

   Explain that the resulting error buffer can still be mapped at creation. <https://github.com/gpuweb/gpuweb/issues/605>

   Explain what are a GPUDevice's [[allowed buffer usages]]. <https://github.com/gpuweb/gpuweb/issues/605>

2. Let b be a new GPUBuffer object.

3. Set b.[[size]] to descriptor.size.

4. Set b.[[usage]] to descriptor.usage.

5. If descriptor.mappedAtCreation is true:

   1. Set b.[[mapping]] to a new ArrayBuffer of size b.[[size]].

   2. Set b.[[mapping_range]] to [0, descriptor.size].

   3. Set b.[[mapped_ranges]] to [].

   4. Set b.[[state]] to mapped at creation.

   Else:

   1. Set b.[[mapping]] to null.

   2. Set b.[[mapping_range]] to null.

   3. Set b.[[mapped_ranges]] to null.

   4. Set b.[[state]] to unmapped.

6. Set each byte of b’s allocation to zero.

7. Return b.

Note: it is valid to set mappedAtCreation to true without MAP_READ or MAP_WRITE in usage. This can be used to set the buffer’s initial data.

5.4. Buffer Destruction

An application that no longer requires a GPUBuffer can choose to lose access to it before garbage collection by calling destroy().

Note: This allows the user agent to reclaim the GPU memory associated with the GPUBuffer once all previously submitted operations using it are complete.

destroy()

Destroys the GPUBuffer.

Called on: GPUBuffer this.

Returns: undefined

1. If the this.[[state]] is mapped or mapped at creation:

   1. Run the steps to unmap this.

2. Set this.[[state]] to destroyed.

Handle error buffers once we have a description of the error monad.

5.5. Buffer Mapping

An application can request to map a GPUBuffer so that they can access its content via ArrayBuffers that represent part of the GPUBuffer's allocations. Mapping a GPUBuffer is requested asynchronously with mapAsync() so that the user agent can ensure the GPU finished using the GPUBuffer before the application can access its content. Once the GPUBuffer is mapped the application can synchronously ask for access to ranges of its content with getMappedRange. A mapped GPUBuffer cannot be used by the GPU and must be unmapped using unmap before work using it can be submitted to the Queue timeline.

Add client-side validation that a mapped buffer can only be unmapped and destroyed on the worker on which it was mapped. Likewise getMappedRange can only be called on that worker. <https://github.com/gpuweb/gpuweb/issues/605>

typedef [EnforceRange] unsigned long GPUMapModeFlags;
interface GPUMapMode {
    const GPUFlagsConstant READ  = 0x0001;
    const GPUFlagsConstant WRITE = 0x0002;
};

mapAsync(mode, offset, size)

Maps the given range of the GPUBuffer and resolves the returned Promise when the GPUBuffer's content is ready to be accessed with getMappedRange().

Called on: GPUBuffer this.

Arguments:

Arguments for the GPUBuffer.mapAsync(mode, offset, size) method.

Parameter	Type	Nullable	Optional	Description
mode	GPUMapModeFlags	✘	✘	Whether the buffer should be mapped for reading or writing.
offset	GPUSize64	✘	✔	Offset in bytes into the buffer to the start of the range to map.
size	GPUSize64	✘	✔	Size in bytes of the range to map.

Returns: Promise<undefined>

Handle error buffers once we have a description of the error monad. <https://github.com/gpuweb/gpuweb/issues/605>

1. If size is unspecified:

   1. Let rangeSize be max(0, this.[[size]] - offset).

   Otherwise, let rangeSize be size.

2. If any of the following conditions are unsatisfied:

   • this is a valid GPUBuffer.

   • offset is a multiple of 8.

   • rangeSize is a multiple of 4.

   • offset + rangeSize is less or equal to this.[[size]]

   • this.[[state]] is unmapped

   • mode contains exactly one of READ or WRITE.

   • If mode contains READ then this.[[usage]] must contain MAP_READ.

   • If mode contains WRITE then this.[[usage]] must contain MAP_WRITE.

   Do we validate that mode contains only valid flags?

   Then:

   1. Record a validation error on the current scope.

   2. Return a promise rejected with an OperationError on the Device timeline.

3. Let p be a new Promise.

4. Set this.[[mapping]] to p.

5. Set this.[[state]] to mapping pending.

6. Set this.[[map_mode]] to mode.

7. Enqueue an operation on the default queue’s Queue timeline that will execute the following:

   1. If this.[[state]] is mapping pending:

      1. Let m be a new ArrayBuffer of size rangeSize.

      2. Set the content of m to the content of this’s allocation starting at offset offset and for rangeSize bytes.

      3. Set this.[[mapping]] to m.

      4. Set this.[[state]] to mapped.

      5. Set this.[[mapping_range]] to [offset, offset + rangeSize].

      6. Set this.[[mapped_ranges]] to [].

   2. Resolve p.

8. Return p.

getMappedRange(offset, size)

Returns a ArrayBuffer with the contents of the GPUBuffer in the given mapped range.

Called on: GPUBuffer this.

Arguments:

Arguments for the GPUBuffer.getMappedRange(offset, size) method.

Parameter	Type	Nullable	Optional	Description
offset	GPUSize64	✘	✔	Offset in bytes into the buffer to return buffer contents from.
size	GPUSize64	✘	✔	Size in bytes of the ArrayBuffer to return.

Returns: ArrayBuffer

1. If size is unspecified:

   1. Let rangeSize be max(0, this.[[size]] - offset).

   Otherwise, let rangeSize be size.

2. If any of the following conditions are unsatisfied, throw an OperationError and stop.

   • this.[[state]] is mapped or mapped at creation.

   • offset is a multiple of 8.

   • rangeSize is a multiple of 4.

   • offset is greater than or equal to this.[[mapping_range]][0].

   • offset + rangeSize is less than or equal to this.[[mapping_range]][1].

   • [offset, offset + rangeSize) does not overlap another range in this.[[mapped_ranges]].

   Note: It is always valid to get mapped ranges of a GPUBuffer that is mapped at creation, even if it is invalid, because the Content timeline might not know it is invalid.

   Consider aligning mapAsync offset to 8 to match this.

3. Let m be a new ArrayBuffer of size rangeSize pointing at the content of this.[[mapping]] at offset offset - this.[[mapping_range]][0].

4. Append m to this.[[mapped_ranges]].

5. Return m.

unmap()

Unmaps the mapped range of the GPUBuffer and makes it’s contents available for use by the GPU again.

Called on: GPUBuffer this.

Returns: undefined

1. If any of the following conditions are unsatisfied, generate a validation error and stop.

   • this.[[state]] is not unmapped

   • this.[[state]] is not destroyed

   Note: It is valid to unmap an error GPUBuffer that is mapped at creation because the Content timeline might not know it is an error GPUBuffer.

2. If this.[[state]] is mapping pending:

   1. Reject [[mapping]] with an AbortError.

   2. Set this.[[mapping]] to null.

3. If this.[[state]] is mapped or mapped at creation:

   1. If one of the two following conditions holds:

      • this.[[state]] is mapped at creation

      • this.[[state]] is mapped and this.[[map_mode]] contains WRITE

      Then:

      1. Enqueue an operation on the default queue’s Queue timeline that updates the this.[[mapping_range]] of this’s allocation to the content of this.[[mapping]].

   2. Detach each ArrayBuffer in this.[[mapped_ranges]] from its content.

   3. Set this.[[mapping]] to null.

   4. Set this.[[mapping_range]] to null.

   5. Set this.[[mapped_ranges]] to null.

4. Set this.[[state]] to unmapped.

Note: When a MAP_READ buffer (not currently mapped at creation) is unmapped, any local modifications done by the application to the mapped ranges ArrayBuffer are discarded and will not affect the content of follow-up mappings.

6. Textures and Texture Views

define texture (internal object)

define mipmap level, array layer, aspect, slice (concepts)

6.1. GPUTexture

[Serializable]
interface GPUTexture {
    GPUTextureView createView(optional GPUTextureViewDescriptor descriptor = {});

    undefined destroy();
};
GPUTexture includes GPUObjectBase;

GPUTexture has the following internal slots:

[[textureSize]] of type GPUExtent3D.

The size of the GPUTexture in texels in mipmap level 0.

[[mipLevelCount]] of type GPUIntegerCoordinate.

The total number of the mipmap levels of the GPUTexture.

[[sampleCount]] of type GPUSize32.

The number of samples in each texel of the GPUTexture.

[[dimension]] of type GPUTextureDimension.

The dimension of the GPUTexture.

[[format]] of type GPUTextureFormat.

The format of the GPUTexture.

[[textureUsage]] of type GPUTextureUsageFlags.

The allowed usages for this GPUTexture.

6.1.1. Texture Creation

dictionary GPUTextureDescriptor : GPUObjectDescriptorBase {
    required GPUExtent3D size;
    GPUIntegerCoordinate mipLevelCount = 1;
    GPUSize32 sampleCount = 1;
    GPUTextureDimension dimension = "2d";
    required GPUTextureFormat format;
    required GPUTextureUsageFlags usage;
};

enum GPUTextureDimension {
    "1d",
    "2d",
    "3d"
};

typedef [EnforceRange] unsigned long GPUTextureUsageFlags;
interface GPUTextureUsage {
    const GPUFlagsConstant COPY_SRC          = 0x01;
    const GPUFlagsConstant COPY_DST          = 0x02;
    const GPUFlagsConstant SAMPLED           = 0x04;
    const GPUFlagsConstant STORAGE           = 0x08;
    const GPUFlagsConstant RENDER_ATTACHMENT = 0x10;
};

createTexture(descriptor)

Creates a GPUTexture.

Called on: GPUDevice this.

Arguments:

Arguments for the GPUDevice.createTexture(descriptor) method.

Parameter	Type	Nullable	Optional	Description
descriptor	GPUTextureDescriptor	✘	✘	Description of the GPUTexture to create.

Returns: GPUTexture

Describe createTexture() algorithm steps.

6.1.2. Texture Destruction

An application that no longer requires a GPUTexture can choose to lose access to it before garbage collection by calling destroy().

Note: This allows the user agent to reclaim the GPU memory associated with the GPUTexture once all previously submitted operations using it are complete.

destroy()

Destroys the GPUTexture.

Called on: GPUTexture this.

Returns: undefined

Describe destroy() algorithm steps.

6.2. GPUTextureView

interface GPUTextureView {
};
GPUTextureView includes GPUObjectBase;

GPUTextureView has the following internal slots:

[[texture]]

The GPUTexture into which this is a view.

[[descriptor]]

The GPUTextureViewDescriptor describing this texture view.

All optional fields of GPUTextureViewDescriptor are defined.

6.2.1. Texture View Creation

dictionary GPUTextureViewDescriptor : GPUObjectDescriptorBase {
    GPUTextureFormat format;
    GPUTextureViewDimension dimension;
    GPUTextureAspect aspect = "all";
    GPUIntegerCoordinate baseMipLevel = 0;
    GPUIntegerCoordinate mipLevelCount;
    GPUIntegerCoordinate baseArrayLayer = 0;
    GPUIntegerCoordinate arrayLayerCount;
};

Make this a standalone algorithm used in the createView algorithm.

The references to GPUTextureDescriptor here should actually refer to internal slots of a texture internal object once we have one.

enum GPUTextureViewDimension {
    "1d",
    "2d",
    "2d-array",
    "cube",
    "cube-array",
    "3d"
};

enum GPUTextureAspect {
    "all",
    "stencil-only",
    "depth-only"
};

createView(descriptor)

Creates a GPUTextureView.

Called on: GPUTexture this.

Arguments:

Arguments for the GPUTexture.createView(descriptor) method.

Parameter	Type	Nullable	Optional	Description
descriptor	GPUTextureViewDescriptor	✘	✔	Description of the GPUTextureView to create.

Returns: view, of type GPUTextureView.

write definition. this descriptor view

6.3. Texture Formats

The name of the format specifies the order of components, bits per component, and data type for the component.

• r, g, b, a = red, green, blue, alpha

• unorm = unsigned normalized

• snorm = signed normalized

• uint = unsigned int

• sint = signed int

• float = floating point

If the format has the -srgb suffix, then sRGB conversions from gamma to linear and vice versa are applied during the reading and writing of color values in the shader. Compressed texture formats are provided by features. Their naming should follow the convention here, with the texture name as a prefix. e.g. etc2-rgba8unorm.

The texel block is a single addressable element of the textures in pixel-based GPUTextureFormats, and a single compressed block of the textures in block-based compressed GPUTextureFormats.

The texel block width and texel block height specifies the dimension of one texel block.

• For pixel-based GPUTextureFormats, the texel block width and texel block height are always 1.

• For block-based compressed GPUTextureFormats, the texel block width is the number of texels in each row of one texel block, and the texel block height is the number of texel rows in one texel block.

The texel block size of a GPUTextureFormat is the number of bytes to store one texel block. The texel block size of each GPUTextureFormat is constant except for "stencil8", "depth24plus", and "depth24plus-stencil8".

enum GPUTextureFormat {
    // 8-bit formats
    "r8unorm",
    "r8snorm",
    "r8uint",
    "r8sint",

    // 16-bit formats
    "r16uint",
    "r16sint",
    "r16float",
    "rg8unorm",
    "rg8snorm",
    "rg8uint",
    "rg8sint",

    // 32-bit formats
    "r32uint",
    "r32sint",
    "r32float",
    "rg16uint",
    "rg16sint",
    "rg16float",
    "rgba8unorm",
    "rgba8unorm-srgb",
    "rgba8snorm",
    "rgba8uint",
    "rgba8sint",
    "bgra8unorm",
    "bgra8unorm-srgb",
    // Packed 32-bit formats
    "rgb9e5ufloat",
    "rgb10a2unorm",
    "rg11b10ufloat",

    // 64-bit formats
    "rg32uint",
    "rg32sint",
    "rg32float",
    "rgba16uint",
    "rgba16sint",
    "rgba16float",

    // 128-bit formats
    "rgba32uint",
    "rgba32sint",
    "rgba32float",

    // Depth and stencil formats
    "stencil8",
    "depth16unorm",
    "depth24plus",
    "depth24plus-stencil8",
    "depth32float",

    // BC compressed formats usable if "texture-compression-bc" is both
    // supported by the device/user agent and enabled in requestDevice.
    "bc1-rgba-unorm",
    "bc1-rgba-unorm-srgb",
    "bc2-rgba-unorm",
    "bc2-rgba-unorm-srgb",
    "bc3-rgba-unorm",
    "bc3-rgba-unorm-srgb",
    "bc4-r-unorm",
    "bc4-r-snorm",
    "bc5-rg-unorm",
    "bc5-rg-snorm",
    "bc6h-rgb-ufloat",
    "bc6h-rgb-float",
    "bc7-rgba-unorm",
    "bc7-rgba-unorm-srgb",

    // "depth24unorm-stencil8" feature
    "depth24unorm-stencil8",

    // "depth32float-stencil8" feature
    "depth32float-stencil8",
};

The depth aspect of the "depth24plus") and "depth24plus-stencil8") formats may be implemented as either a 24-bit unsigned normalized value ("depth24unorm") or a 32-bit IEEE 754 floating point value ("depth32float").

add something on GPULimits that gives an estimate of the bytes per texel of "stencil8"

The stencil8) format may be implemented as either a real "stencil8", or "depth24stencil8", where the depth aspect is hidden and inaccessible.

Note: While the precision of depth32float is strictly higher than the precision of depth24unorm for all values in the representable range (0.0 to 1.0), note that the set of representable values is not exactly the same: for depth24unorm, 1 ULP has a constant value of 1 / (2²⁴ − 1); for depth32float, 1 ULP has a variable value no greater than 1 / (2²⁴).

"rgb9e5ufloat" cannot be used as a color attachment.

7. Samplers

7.1. GPUSampler

A GPUSampler encodes transformations and filtering information that can be used in a shader to interpret texture resource data.

GPUSamplers are created via GPUDevice.createSampler(optional descriptor) that returns a new sampler object.

interface GPUSampler {
};
GPUSampler includes GPUObjectBase;

GPUSampler has the following internal slots:

[[descriptor]], of type GPUSamplerDescriptor, readonly

The GPUSamplerDescriptor with which the GPUSampler was created.

[[isComparison]] of type boolean.

Whether the GPUSampler is used as a comparison sampler.

[[isFiltering]] of type boolean.

Whether the GPUSampler weights multiple samples of a texture.

7.2. Sampler Creation

7.2.1. GPUSamplerDescriptor

A GPUSamplerDescriptor specifies the options to use to create a GPUSampler.

dictionary GPUSamplerDescriptor : GPUObjectDescriptorBase {
    GPUAddressMode addressModeU = "repeat";
    GPUAddressMode addressModeV = "repeat";
    GPUAddressMode addressModeW = "repeat";
    GPUFilterMode magFilter = "nearest";
    GPUFilterMode minFilter = "nearest";
    GPUFilterMode mipmapFilter = "nearest";
    float lodMinClamp = 0;
    float lodMaxClamp = 0xffffffff; // TODO: What should this be? Was Number.MAX_VALUE.
    GPUCompareFunction compare;
    [Clamp] unsigned short maxAnisotropy = 1;
};

• addressModeU, addressModeV, and addressModeW specify the address modes for the texture width, height, and depth coordinates, respectively.

• magFilter specifies the sampling behavior when the sample footprint is smaller than or equal to one texel.

• minFilter specifies the sampling behavior when the sample footprint is larger than one texel.

• mipmapFilter specifies behavior for sampling between two mipmap levels.

• lodMinClamp and lodMaxClamp specify the minimum and maximum levels of detail, respectively, used internally when sampling a texture.

• If compare is provided, the sampler will be a comparison sampler with the specified GPUCompareFunction.

• maxAnisotropy specifies the maximum anisotropy value clamp used by the sampler.

  • It must be ≥ 1.

  Note: most implementations support maxAnisotropy values in range between 1 and 16, inclusive.

explain how LOD is calculated and if there are differences here between platforms. Issue: explain what anisotropic sampling is

GPUAddressMode describes the behavior of the sampler if the sample footprint extends beyond the bounds of the sampled texture.

Describe a "sample footprint" in greater detail.

enum GPUAddressMode {
    "clamp-to-edge",
    "repeat",
    "mirror-repeat"
};

"clamp-to-edge"

Texture coordinates are clamped between 0.0 and 1.0, inclusive.

"repeat"

Texture coordinates wrap to the other side of the texture.

"mirror-repeat"

Texture coordinates wrap to the other side of the texture, but the texture is flipped when the integer part of the coordinate is odd.

GPUFilterMode describes the behavior of the sampler if the sample footprint does not exactly match one texel.

enum GPUFilterMode {
    "nearest",
    "linear"
};

"nearest"

Return the value of the texel nearest to the texture coordinates.

"linear"

Select two texels in each dimension and return a linear interpolation between their values.

GPUCompareFunction specifies the behavior of a comparison sampler. If a comparison sampler is used in a shader, an input value is compared to the sampled texture value, and the result of this comparison test (0.0f for pass, or 1.0f for fail) is used in the filtering operation.

describe how filtering interacts with comparison sampling.

enum GPUCompareFunction {
    "never",
    "less",
    "equal",
    "less-equal",
    "greater",
    "not-equal",
    "greater-equal",
    "always"
};

"never"

Comparison tests never pass.

"less"

A provided value passes the comparison test if it is less than the sampled value.

"equal"

A provided value passes the comparison test if it is equal to the sampled value.

"less-equal"

A provided value passes the comparison test if it is less than or equal to the sampled value.

"greater"

A provided value passes the comparison test if it is greater than the sampled value.

"not-equal"

A provided value passes the comparison test if it is not equal to the sampled value.

"greater-equal"

A provided value passes the comparison test if it is greater than or equal to the sampled value.

"always"

Comparison tests always pass.

createSampler(descriptor)

Creates a GPUBindGroupLayout.

Called on: GPUDevice this.

Arguments:

Arguments for the GPUDevice.createSampler(descriptor) method.

Parameter	Type	Nullable	Optional	Description
descriptor	GPUSamplerDescriptor	✘	✔	Description of the GPUSampler to create.

Returns: GPUSampler

1. Let s be a new GPUSampler object.

2. Set s.[[descriptor]] to descriptor.

3. Set s.[[isComparison]] to false if the compare attribute of s.[[descriptor]] is null or undefined. Otherwise, set it to true.

4. Set s.[[isFiltering]] to false if none of minFilter, magFilter, or mipmapFilter has the value of "linear". Otherwise, set it to true.

5. Return s.

Valid Usage

• If descriptor is not null or undefined:

  • If validating GPUSamplerDescriptor(this, descriptor) returns false:

    1. Generate a GPUValidationError in the current scope with appropriate error message.

    2. Create a new invalid GPUSampler and return the result.

8. Resource Binding

8.1. GPUBindGroupLayout

A GPUBindGroupLayout defines the interface between a set of resources bound in a GPUBindGroup and their accessibility in shader stages.

[Serializable]
interface GPUBindGroupLayout {
};
GPUBindGroupLayout includes GPUObjectBase;

8.1.1. Creation

A GPUBindGroupLayout is created via GPUDevice.createBindGroupLayout().

dictionary GPUBindGroupLayoutDescriptor : GPUObjectDescriptorBase {
    required sequence<GPUBindGroupLayoutEntry> entries;
};

A GPUBindGroupLayoutEntry describes a single shader resource binding to be included in a GPUBindGroupLayout.

typedef [EnforceRange] unsigned long GPUShaderStageFlags;
interface GPUShaderStage {
    const GPUFlagsConstant VERTEX   = 0x1;
    const GPUFlagsConstant FRAGMENT = 0x2;
    const GPUFlagsConstant COMPUTE  = 0x4;
};

dictionary GPUBindGroupLayoutEntry {
    required GPUIndex32 binding;
    required GPUShaderStageFlags visibility;

    GPUBufferBindingLayout buffer;
    GPUSamplerBindingLayout sampler;
    GPUTextureBindingLayout texture;
    GPUStorageTextureBindingLayout storageTexture;
};

GPUBindGroupLayoutEntry dictionaries have the following members:

binding, of type GPUIndex32

A unique identifier for a resource binding within a GPUBindGroupLayoutEntry, a corresponding GPUBindGroupEntry, and the GPUShaderModules.

visibility, of type GPUShaderStageFlags

A bitset of the members of GPUShaderStage. Each set bit indicates that a GPUBindGroupLayoutEntry's resource will be accessible from the associated shader stage.

buffer, of type GPUBufferBindingLayout

When not undefined indicates the binding resource type for this GPUBindGroupLayoutEntry is GPUBufferBinding.

sampler, of type GPUSamplerBindingLayout

When not undefined indicates the binding resource type for this GPUBindGroupLayoutEntry is GPUSampler.

texture, of type GPUTextureBindingLayout

When not undefined indicates the binding resource type for this GPUBindGroupLayoutEntry is GPUTextureView.

storageTexture, of type GPUStorageTextureBindingLayout

When not undefined indicates the binding resource type for this GPUBindGroupLayoutEntry is GPUTextureView.

The binding member of a GPUBindGroupLayoutEntry is determined by which member of the GPUBindGroupLayoutEntry is defined: buffer, sampler, texture, or storageTexture. Only one may be defined for any given GPUBindGroupLayoutEntry. Each member has an associated GPUBindingResource type and each binding type has an associated internal usage, given by this table:

enum GPUBufferBindingType {
    "uniform",
    "storage",
    "readonly-storage",
};

dictionary GPUBufferBindingLayout {
    GPUBufferBindingType type = "uniform";
    boolean hasDynamicOffset = false;
    GPUSize64 minBindingSize = 0;
};

GPUBufferBindingLayout dictionaries have the following members:

type, of type GPUBufferBindingType, defaulting to "uniform"

Indicates the type required for buffers bound to this bindings.

hasDynamicOffset, of type boolean, defaulting to false

Indicates whether this binding requires a dynamic offset.

minBindingSize, of type GPUSize64, defaulting to 0

May be used to indicate the minimum buffer binding size.

enum GPUSamplerBindingType {
    "filtering",
    "non-filtering",
    "comparison",
};

dictionary GPUSamplerBindingLayout {
    GPUSamplerBindingType type = "filtering";
};

GPUSamplerBindingLayout dictionaries have the following members:

type, of type GPUSamplerBindingType, defaulting to "filtering"

Indicates the required type of a sampler bound to this bindings.

enum GPUTextureSampleType {
  "float",
  "unfilterable-float",
  "depth",
  "sint",
  "uint",
};

dictionary GPUTextureBindingLayout {
    GPUTextureSampleType sampleType = "float";
    GPUTextureViewDimension viewDimension = "2d";
    boolean multisampled = false;
};

consider making sampleType truly optional.

GPUTextureBindingLayout dictionaries have the following members:

sampleType, of type GPUTextureSampleType, defaulting to "float"

Indicates the type required for texture views bound to this binding.

viewDimension, of type GPUTextureViewDimension, defaulting to "2d"

Indicates the required dimension for texture views bound to this binding.

Note: This enables Metal-based WebGPU implementations to back the respective bind groups with MTLArgumentBuffer objects that are more efficient to bind at run-time.

multisampled, of type boolean, defaulting to false

Inicates whether or not texture views bound to this binding must be multisampled.

enum GPUStorageTextureAccess {
    "readonly",
    "writeonly",
};

dictionary GPUStorageTextureBindingLayout {
    required GPUStorageTextureAccess access;
    required GPUTextureFormat format;
    GPUTextureViewDimension viewDimension = "2d";
};

consider making format truly optional.

GPUStorageTextureBindingLayout dictionaries have the following members:

access, of type GPUStorageTextureAccess

Indicates whether texture views bound to this binding will be bound for read-only or write-only access.

format, of type GPUTextureFormat

The required format of texture views bound to this binding.

viewDimension, of type GPUTextureViewDimension, defaulting to "2d"

Indicates the required dimension for texture views bound to this binding.

Note: This enables Metal-based WebGPU implementations to back the respective bind groups with MTLArgumentBuffer objects that are more efficient to bind at run-time.

A GPUBindGroupLayout object has the following internal slots:

[[entryMap]] of type ordered map<GPUSize32, GPUBindGroupLayoutEntry>.

The map of binding indices pointing to the GPUBindGroupLayoutEntrys, which this GPUBindGroupLayout describes.

[[dynamicOffsetCount]] of type GPUSize32.

The number of buffer bindings with dynamic offsets in this GPUBindGroupLayout.

createBindGroupLayout(descriptor)

Creates a GPUBindGroupLayout.

Called on: GPUDevice this.

Arguments:

Arguments for the GPUDevice.createBindGroupLayout(descriptor) method.

Parameter	Type	Nullable	Optional	Description
descriptor	GPUBindGroupLayoutDescriptor	✘	✘	Description of the GPUBindGroupLayout to create.

Returns: GPUBindGroupLayout

1. Let layout be a new valid GPUBindGroupLayout object.

2. Issue the following steps on the Device timeline of this:

   1. If any of the following conditions are unsatisfied:

      • this is a valid GPUDevice.

      • The binding of each entry in descriptor is unique.

      • For each shader stage, the number of entries in descriptor with a layout entry binding type of "uniform" ≤ GPULimits.maxUniformBuffersPerShaderStage.

      • For each shader stage, the number of entries in descriptor with a layout entry binding type of "storage" ≤ GPULimits.maxStorageBuffersPerShaderStage.

      • For each shader stage, the number of entries in descriptor with a binding member of texture ≤ GPULimits.maxSampledTexturesPerShaderStage.

      • For each shader stage, the number of entries in descriptor with a binding member of storageTexture ≤ GPULimits.maxStorageTexturesPerShaderStage.

      • For each shader stage, the number of entries in descriptor with a binding member of sampler ≤ GPULimits.maxSamplersPerShaderStage.

      • The number of entries in descriptor with a layout entry binding type of "uniform" and buffer.hasDynamicOffset true ≤ GPULimits.maxDynamicUniformBuffersPerPipelineLayout.

      • The number of entries in descriptor with a layout entry binding type of "storage" and buffer.hasDynamicOffset true ≤ GPULimits.maxDynamicStorageBuffersPerPipelineLayout.

      • For each GPUBindGroupLayoutEntry bindingDescriptor in descriptor.entries:

        • Let bufferLayout be bindingDescriptor.buffer

        • Let samplerLayout be bindingDescriptor.sampler

        • Let textureLayout be bindingDescriptor.texture

        • Let storageTextureLayout be bindingDescriptor.storageTexture

        • Exactly one of bufferLayout, samplerLayout, textureLayout, or storageTextureLayout are not undefined.

        • If bindingDescriptor.visibility includes VERTEX:

          • The layout entry binding type of bindingDescriptor is not "readonly-storage" or "writeonly".

        • If the textureLayout is not undefined and textureLayout.multisampled is true:

          • textureLayout.viewDimension is "2d".

          • textureLayout.sampleType is not "float".

        • If storageTextureLayout is not undefined:

          • storageTextureLayout.viewDimension is not "cube" or "cube-array".

          • storageTextureLayout.format must be a format which can support storage usage.

      Then:

      1. Generate a GPUValidationError in the current scope with appropriate error message.

      2. Make layout invalid and return layout.

   2. Set layout.[[dynamicOffsetCount]] to the number of entries in descriptor where buffer is not undefined and buffer.hasDynamicOffset is true.

   3. For each GPUBindGroupLayoutEntry bindingDescriptor in descriptor.entries:

      1. Insert bindingDescriptor into layout.[[entryMap]] with the key of bindingDescriptor.binding.

3. Return layout.

8.1.2. Compatibility

If bind groups layouts are group-equivalent they can be interchangeably used in all contents.

8.2. GPUBindGroup

A GPUBindGroup defines a set of resources to be bound together in a group and how the resources are used in shader stages.

interface GPUBindGroup {
};
GPUBindGroup includes GPUObjectBase;

8.2.1. Bind Group Creation

A GPUBindGroup is created via GPUDevice.createBindGroup().

dictionary GPUBindGroupDescriptor : GPUObjectDescriptorBase {
    required GPUBindGroupLayout layout;
    required sequence<GPUBindGroupEntry> entries;
};

A GPUBindGroupEntry describes a single resource to be bound in a GPUBindGroup.

typedef (GPUSampler or GPUTextureView or GPUBufferBinding) GPUBindingResource;

dictionary GPUBindGroupEntry {
    required GPUIndex32 binding;
    required GPUBindingResource resource;
};

dictionary GPUBufferBinding {
    required GPUBuffer buffer;
    GPUSize64 offset = 0;
    GPUSize64 size;
};

• size: If undefined, specifies the range starting at offset and ending at the end of the buffer.

A GPUBindGroup object has the following internal slots:

[[layout]] of type GPUBindGroupLayout.

The GPUBindGroupLayout associated with this GPUBindGroup.

[[entries]] of type sequence<GPUBindGroupEntry>.

The set of GPUBindGroupEntrys this GPUBindGroup describes.

[[usedResources]] of type ordered map<subresource, list<internal usage>>.

The set of buffer and texture subresources used by this bind group, associated with lists of the internal usage flags.

createBindGroup(descriptor)

Creates a GPUBindGroup.

Called on: GPUDevice this.

Arguments:

Arguments for the GPUDevice.createBindGroup(descriptor) method.

Parameter	Type	Nullable	Optional	Description
descriptor	GPUBindGroupDescriptor	✘	✘	Description of the GPUBindGroup to create.

Returns: GPUBindGroup

1. Let bindGroup be a new valid GPUBindGroup object.

2. Issue the following steps on the Device timeline of this:

   1. If any of the following conditions are unsatisfied:

      • this is a valid GPUDevice.

      • descriptor.layout is valid to use with this.

      • The number of entries of descriptor.layout is exactly equal to the number of descriptor.entries.

      For each GPUBindGroupEntry bindingDescriptor in descriptor.entries:

      • Let resource be bindingDescriptor.resource.

      • There is exactly one GPUBindGroupLayoutEntry layoutBinding in descriptor.layout.entries such that layoutBinding.binding equals to bindingDescriptor.binding.

      • If the defined binding member for layoutBinding is

        sampler

        • resource is a GPUSampler.

        • resource is valid to use with this.

        • If the layout entry binding type of layoutBinding is

          "filtering"

          resource.[[isComparison]] is false.

          "non-filtering"

          resource.[[isFiltering]] is false. resource.[[isComparison]] is false.

          "comparison"

          resource.[[isComparison]] is true.

        texture

        • resource is a GPUTextureView.

        • resource is valid to use with this.

        • Let texture be resource.[[texture]].

        • layoutBinding.texture.viewDimension is equal to resource’s dimension.

        • layoutBinding.texture.sampleType is compatible with resource’s format.

        • texture’s usage includes SAMPLED.

        • If layoutBinding.texture.multisampled is true, texture’s sampleCount > 1, Otherwise texture’s sampleCount is 1.

        storageTexture

        • resource is a GPUTextureView.

        • resource is valid to use with this.

        • Let texture be resource.[[texture]].

        • layoutBinding.storageTexture.viewDimension is equal to resource’s dimension.

        • layoutBinding.storageTexture.format is equal to resource.[[descriptor]].format.

        • texture’s usage includes STORAGE.

        buffer

        • resource is a GPUBufferBinding.

        • resource.buffer is valid to use with this.

        • The bound part designated by resource.offset and resource.size resides inside the buffer.

        • If layoutBinding.buffer.minBindingSize is not undefined:

          • The effective binding size, that is either explict in resource.size or derived from resource.offset and the full size of the buffer, is greater than or equal to layoutBinding.buffer.minBindingSize.

        • If layoutBinding.buffer.type is

          "uniform"

          resource.buffer.usage includes UNIFORM.

          resource.size ≤ maxUniformBufferBindingSize.

          This validation should take into account the default when size is not set. Also should size default to the buffer.byteLength - offset or min(buffer.byteLength - offset, limits.maxUniformBufferBindingSize)?

          "storage" or "readonly-storage"

          resource.buffer.usage includes STORAGE.

          resource.size ≤ maxStorageBufferBindingSize.

      define the association between texture formats and component types

      Then:

      1. Generate a GPUValidationError in the current scope with appropriate error message.

      2. Make bindGroup invalid and return bindGroup.

   2. Let bindGroup.[[layout]] = descriptor.layout.

   3. Let bindGroup.[[entries]] = descriptor.entries.

   4. Let bindGroup.[[usedResources]] = {}.

   5. For each GPUBindGroupEntry bindingDescriptor in descriptor.entries:

      1. Let internalUsage be the binding usage for layoutBinding.

      2. Each subresource seen by resource is added to [[usedResources]] as internalUsage.

3. Return bindGroup.

define the "effective buffer binding size" separately.

8.3. GPUPipelineLayout

A GPUPipelineLayout defines the mapping between resources of all GPUBindGroup objects set up during command encoding in setBindGroup, and the shaders of the pipeline set by GPURenderEncoderBase.setPipeline or GPUComputePassEncoder.setPipeline.

The full binding address of a resource can be defined as a trio of:

1. shader stage mask, to which the resource is visible

2. bind group index

3. binding number

The components of this address can also be seen as the binding space of a pipeline. A GPUBindGroup (with the corresponding GPUBindGroupLayout) covers that space for a fixed bind group index. The contained bindings need to be a superset of the resources used by the shader at this bind group index.

[Serializable]
interface GPUPipelineLayout {
};
GPUPipelineLayout includes GPUObjectBase;

GPUPipelineLayout has the following internal slots:

[[bindGroupLayouts]] of type list<GPUBindGroupLayout>.

The GPUBindGroupLayout objects provided at creation in GPUPipelineLayoutDescriptor.bindGroupLayouts.

Note: using the same GPUPipelineLayout for many GPURenderPipeline or GPUComputePipeline pipelines guarantees that the user agent doesn’t need to rebind any resources internally when there is a switch between these pipelines.

should this example and the note be moved to some "best practices" document?

Note: the expected usage of the GPUPipelineLayout is placing the most common and the least frequently changing bind groups at the "bottom" of the layout, meaning lower bind group slot numbers, like 0 or 1. The more frequently a bind group needs to change between draw calls, the higher its index should be. This general guideline allows the user agent to minimize state changes between draw calls, and consequently lower the CPU overhead.

8.3.1. Creation

A GPUPipelineLayout is created via GPUDevice.createPipelineLayout().

dictionary GPUPipelineLayoutDescriptor : GPUObjectDescriptorBase {
    required sequence<GPUBindGroupLayout> bindGroupLayouts;
};

createPipelineLayout(descriptor)

Creates a GPUPipelineLayout.

Called on: GPUDevice this.

Arguments:

Arguments for the GPUDevice.createPipelineLayout(descriptor) method.

Parameter	Type	Nullable	Optional	Description
descriptor	GPUPipelineLayoutDescriptor	✘	✘	Description of the GPUPipelineLayout to create.

Returns: GPUPipelineLayout

1. If any of the following conditions are unsatisfied:

   • this is a valid GPUDevice.

   • There is GPULimits.maxBindGroups or fewer elements in descriptor.bindGroupLayouts.

   • Every GPUBindGroupLayout in descriptor.bindGroupLayouts is valid to use with this.

   Then:

   1. Generate a GPUValidationError in the current scope with appropriate error message.

   2. Create a new invalid GPUPipelineLayout and return the result.

2. Let pl be a new GPUPipelineLayout object.

3. Set the pl.[[bindGroupLayouts]] to descriptor.bindGroupLayouts.

4. Return pl.

there will be more limits applicable to the whole pipeline layout.

Note: two GPUPipelineLayout objects are considered equivalent for any usage if their internal [[bindGroupLayouts]] sequences contain GPUBindGroupLayout objects that are group-equivalent.

9. Shader Modules

9.1. GPUShaderModule

enum GPUCompilationMessageType {
    "error",
    "warning",
    "info"
};

[Serializable]
interface GPUCompilationMessage {
    readonly attribute DOMString message;
    readonly attribute GPUCompilationMessageType type;
    readonly attribute unsigned long long lineNum;
    readonly attribute unsigned long long linePos;
};

[Serializable]
interface GPUCompilationInfo {
    readonly attribute FrozenArray<GPUCompilationMessage> messages;
};

[Serializable]
interface GPUShaderModule {
    Promise<GPUCompilationInfo> compilationInfo();
};
GPUShaderModule includes GPUObjectBase;

GPUShaderModule is Serializable. It is a reference to an internal shader module object, and Serializable means that the reference can be copied between realms (threads/workers), allowing multiple realms to access it concurrently. Since GPUShaderModule is immutable, there are no race conditions.

9.1.1. Shader Module Creation

dictionary GPUShaderModuleDescriptor : GPUObjectDescriptorBase {
    required USVString code;
    object sourceMap;
};

sourceMap, if defined, MAY be interpreted as a source-map-v3 format. (https://sourcemaps.info/spec.html) Source maps are optional, but serve as a standardized way to support dev-tool integration such as source-language debugging.

createShaderModule(descriptor)

Creates a GPUShaderModule.

Called on: GPUDevice this.

Arguments:

Arguments for the GPUDevice.createShaderModule(descriptor) method.

Parameter	Type	Nullable	Optional	Description
descriptor	GPUShaderModuleDescriptor	✘	✘	Description of the GPUShaderModule to create.

Returns: GPUShaderModule

Describe createShaderModule() algorithm steps.

9.1.2. Shader Module Compilation Information

compilationInfo()

Returns any messages generated during the GPUShaderModule's compilation.

Called on: GPUShaderModule this.

Returns: Promise<GPUCompilationInfo>

Describe compilationInfo() algorithm steps.

10. Pipelines

A pipeline, be it GPUComputePipeline or GPURenderPipeline, represents the complete function done by a combination of the GPU hardware, the driver, and the user agent, that process the input data in the shape of bindings and vertex buffers, and produces some output, like the colors in the output render targets.

Structurally, the pipeline consists of a sequence of programmable stages (shaders) and fixed-function states, such as the blending modes.

Note: Internally, depending on the target platform, the driver may convert some of the fixed-function states into shader code, and link it together with the shaders provided by the user. This linking is one of the reason the object is created as a whole.

This combination state is created as a single object (by GPUDevice.createComputePipeline() or GPUDevice.createRenderPipeline()), and switched as one (by GPUComputePassEncoder.setPipeline or GPURenderEncoderBase.setPipeline correspondingly).

10.1. Base pipelines

dictionary GPUPipelineDescriptorBase : GPUObjectDescriptorBase {
    GPUPipelineLayout layout;
};

interface mixin GPUPipelineBase {
    GPUBindGroupLayout getBindGroupLayout(unsigned long index);
};

GPUPipelineBase has the following internal slots:

[[layout]] of type GPUPipelineLayout.

The definition of the layout of resources which can be used with this.

GPUPipelineBase has the following methods:

getBindGroupLayout(index)

Gets a GPUBindGroupLayout that is compatible with the GPUPipelineBase's GPUBindGroupLayout at index.

Called on: GPUPipelineBase this.

Arguments:

Arguments for the GPUPipelineBase.getBindGroupLayout(index) method.

Parameter	Type	Nullable	Optional	Description
index	unsigned long	✘	✘	Index into the pipeline layout’s [[bindGroupLayouts]] sequence.

Returns: GPUBindGroupLayout

1. If index is greater or equal to maxBindGroups:

   1. Throw a RangeError.

2. If this is not valid:

   1. Return a new error GPUBindGroupLayout.

3. Return a new GPUBindGroupLayout object that references the same internal object as this.[[layout]].[[bindGroupLayouts]][index].

Specify this more properly once we have internal objects for GPUBindGroupLayout. Alternatively only spec is as a new internal objects that’s group-equivalent

Note: Only returning new GPUBindGroupLayout objects ensures no synchronization is necessary between the Content timeline and the Device timeline.

10.1.1. Default pipeline layout

A GPUPipelineBase object that was created without a layout has a default layout created and used instead.

10.1.2. GPUProgrammableStageDescriptor

dictionary GPUProgrammableStageDescriptor {
    required GPUShaderModule module;
    required USVString entryPoint;
};

A GPUProgrammableStageDescriptor describes the entry point in the user-provided GPUShaderModule that controls one of the programmable stages of a pipeline.

is there a match/switch statement in bikeshed?

A resource binding is considered to be statically used by a shader entry point if and only if it’s reachable by the control flow graph of the shader module, starting at the entry point.

10.2. GPUComputePipeline

A GPUComputePipeline is a kind of pipeline that controls the compute shader stage, and can be used in GPUComputePassEncoder.

Compute inputs and outputs are all contained in the bindings, according to the given GPUPipelineLayout. The outputs correspond to buffer bindings with a type of "storage" and storageTexture bindings with a type of "writeonly".

Stages of a compute pipeline:

1. Compute shader

[Serializable]
interface GPUComputePipeline {
};
GPUComputePipeline includes GPUObjectBase;
GPUComputePipeline includes GPUPipelineBase;

10.2.1. Creation

dictionary GPUComputePipelineDescriptor : GPUPipelineDescriptorBase {
    required GPUProgrammableStageDescriptor computeStage;
};

createComputePipeline(descriptor)

Creates a GPUComputePipeline.

Called on: GPUDevice this.

Arguments:

Arguments for the GPUDevice.createComputePipeline(descriptor) method.

Parameter	Type	Nullable	Optional	Description
descriptor	GPUComputePipelineDescriptor	✘	✘	Description of the GPUComputePipeline to create.

Returns: GPUComputePipeline

If any of the following conditions are unsatisfied:

• this is a valid GPUDevice.

• descriptor.layout is valid to use with this.

• validating GPUProgrammableStageDescriptor(COMPUTE, descriptor.computeStage, descriptor.layout) succeeds.

Then:

1. Generate a GPUValidationError in the current scope with appropriate error message.

2. Create a new invalid GPUComputePipeline and return the result.

createReadyComputePipeline(descriptor)

Creates a GPUComputePipeline. The returned Promise resolves when the created pipeline is ready to be used without additional delay.

If pipeline creation fails, the returned Promise resolves to an invalid GPUComputePipeline object.

Note: Use of this method is preferred whenever possible, as it prevents blocking the queue timeline work on pipeline compilation.

Called on: GPUDevice this.

Arguments:

Arguments for the GPUDevice.createReadyComputePipeline(descriptor) method.

Parameter	Type	Nullable	Optional	Description
descriptor	GPUComputePipelineDescriptor	✘	✘	Description of the GPUComputePipeline to create.

Returns: Promise<GPUComputePipeline>

1. Let promise be a new promise.

2. Issue the following steps on the Device timeline of this:

   1. Let pipeline be a new GPUComputePipeline created as if this.createComputePipeline() was called with descriptor;

   2. When pipeline is ready to be used, resolve promise with pipeline.

3. Return promise.

10.3. GPURenderPipeline

A GPURenderPipeline is a kind of pipeline that controls the vertex and fragment shader stages, and can be used in GPURenderPassEncoder as well as GPURenderBundleEncoder.

Render pipeline inputs are:

• bindings, according to the given GPUPipelineLayout

• vertex and index buffers, described by GPUVertexStateDescriptor

• the color attachments, described by GPUColorStateDescriptor

• optionally, the depth-stencil attachment, described by GPUDepthStencilStateDescriptor

Render pipeline outputs are:

• buffer bindings with a type of "storage"

• storageTexture bindings with a access of "writeonly"

• the color attachments, described by GPUColorStateDescriptor

• optionally, depth-stencil attachment, described by GPUDepthStencilStateDescriptor

Stages of a render pipeline:

1. Vertex fetch, controlled by GPUVertexStateDescriptor

2. Vertex shader

3. Primitive assembly, controlled by GPUPrimitiveTopology

4. Rasterization, controlled by GPURasterizationStateDescriptor

5. Fragment shader

6. Stencil test and operation, controlled by GPUDepthStencilStateDescriptor

7. Depth test and write, controlled by GPUDepthStencilStateDescriptor

8. Output merging, controlled by GPUColorStateDescriptor

we need a deeper description of these stages

[Serializable]
interface GPURenderPipeline {
};
GPURenderPipeline includes GPUObjectBase;
GPURenderPipeline includes GPUPipelineBase;

GPURenderPipeline has the following internal slots:

[[descriptor]], of type GPURenderPipelineDescriptor

The GPURenderPipelineDescriptor describing this pipeline.

All optional fields of GPURenderPipelineDescriptor are defined.

[[strip_index_format]], of type GPUIndexFormat?

The format index data this pipeline requires, initially undefined.

10.3.1. Creation

dictionary GPURenderPipelineDescriptor : GPUPipelineDescriptorBase {
    required GPUProgrammableStageDescriptor vertexStage;
    GPUProgrammableStageDescriptor fragmentStage;

    required GPUPrimitiveTopology primitiveTopology;
    GPURasterizationStateDescriptor rasterizationState = {};
    required sequence<GPUColorStateDescriptor> colorStates;
    GPUDepthStencilStateDescriptor depthStencilState;
    GPUVertexStateDescriptor vertexState = {};

    GPUSize32 sampleCount = 1;
    GPUSampleMask sampleMask = 0xFFFFFFFF;
    boolean alphaToCoverageEnabled = false;
};

• vertexStage describes the vertex shader entry point of the pipeline

• fragmentStage describes the fragment shader entry point of the pipeline. If it’s null, the § 10.3.2 No Color Output mode is enabled.

• primitiveTopology configures the primitive assembly stage of the pipeline.

• rasterizationState configures the rasterization stage of the pipeline.

• colorStates describes the color attachments that are written by the pipeline.

• depthStencilState describes the optional depth-stencil attachment that is written by the pipeline.

• vertexState configures the vertex fetch stage of the pipeline.

• sampleCount is the number of MSAA samples that each attachment has to have.

• sampleMask is a binary mask of MSAA samples, according to § 10.3.4 Sample Masking.

• alphaToCoverageEnabled enables the § 10.3.3 Alpha to Coverage mode.

Refactor the shape of the render pipeline descriptor to clearly enumerate the (ordered) list of pipeline stages. And start formalizing the spec text.

10.3.2. No Color Output

In no-color-output mode, pipeline does not produce any color attachment outputs, and the colorStates is expected to be empty.

The pipeline still performs rasterization and produces depth values based on the vertex position output. The depth testing and stencil operations can still be used.

10.3.3. Alpha to Coverage

In alpha-to-coverage mode, an additional alpha-to-coverage mask of MSAA samples is generated based on the alpha component of the fragment shader output value of the colorStates[0].

The algorithm of producing the extra mask is platform-dependent and can vary for different pixels. It guarantees that:

• if alpha is 0.0 or less, the result is 0x0

• if alpha is 1.0 or greater, the result is 0xFFFFFFFF

• if alpha is greater than some other alpha1, then the produced sample mask has at least as many bits set to 1 as the mask for alpha1

10.3.4. Sample Masking

The final sample mask for a pixel is computed as: rasterization mask & sampleMask & shader-output mask.

Only the lower sampleCount bits of the mask are considered.

If the least-significant bit at position N of the final sample mask has value of "0", the sample color outputs (corresponding to sample N) to all attachments of the fragment shader are discarded. Also, no depth test or stencil operations are executed on the relevant samples of the depth-stencil attachment.

Note: the color output for sample N is produced by the fragment shader execution with SV_SampleIndex == N for the current pixel. If the fragment shader doesn’t use this semantics, it’s only executed once per pixel.

The rasterization mask is produced by the rasterization stage, based on the shape of the rasterized polygon. The samples incuded in the shape get the relevant bits 1 in the mask.

The shader-output mask takes the output value of SV_Coverage semantics in the fragment shader. If the semantics is not statically used by the shader, and alphaToCoverageEnabled is enabled, the shader-output mask becomes the alpha-to-coverage mask. Otherwise, it defaults to 0xFFFFFFFF.

link to the semantics of SV_SampleIndex and SV_Coverage in WGSL spec.

createRenderPipeline(descriptor)

Creates a GPURenderPipeline.

Called on: GPUDevice this.

Arguments:

Arguments for the GPUDevice.createRenderPipeline(descriptor) method.

Parameter	Type	Nullable	Optional	Description
descriptor	GPURenderPipelineDescriptor	✘	✘	Description of the GPURenderPipeline to create.

Returns: GPURenderPipeline

1. Let pipeline be a new valid GPURenderPipeline object.

2. Issue the following steps on the Device timeline of this:

   1. If any of the following conditions are unsatisfied:

      • this is a valid GPUDevice.

      • descriptor.layout is valid to use with this.

      • validating GPUProgrammableStageDescriptor(VERTEX, descriptor.vertexStage, descriptor.layout) succeeds.

      • If descriptor.fragmentStage is not null:

        • validating GPUProgrammableStageDescriptor(FRAGMENT, descriptor.fragmentStage, descriptor.layout) succeeds.

      • descriptor.colorStates.length is less than or equal to 4.

      • Each colorState layout descriptor in the list descriptor.colorStates passes validating GPUColorStateDescriptor(colorState).

      • validating GPUVertexStateDescriptor(descriptor.vertexState, descriptor.vertexStage) passes.

      • If descriptor.alphaToCoverageEnabled is true:

        • descriptor.sampleCount is greater than 1.

      • If the output SV_Coverage semantics is statically used by descriptor.fragmentStage:

        • descriptor.alphaToCoverageEnabled is false.

      • If descriptor.primitiveTopology is:

        "line-strip" or "triangle-strip"

        descriptor.vertexState.indexFormat is not undefined

        Otherwise

        descriptor.vertexState.indexFormat is undefined

      Then:

      1. Generate a GPUValidationError in the current scope with appropriate error message.

      2. Make pipeline invalid.

   2. Set pipeline.[[descriptor]] to descriptor.

   3. If descriptor.primitiveTopology is "line-strip" or "triangle-strip":

      1. Set pipeline.[[strip_index_format]] to descriptor.vertexState.indexFormat.

3. Return pipeline.

need a proper limit for the maximum number of color targets.

need a more detailed validation of the render states.

need description of the render states.

createReadyRenderPipeline(descriptor)

Creates a GPURenderPipeline. The returned Promise resolves when the created pipeline is ready to be used without additional delay.

If pipeline creation fails, the returned Promise resolves to an invalid GPURenderPipeline object.

Note: Use of this method is preferred whenever possible, as it prevents blocking the queue timeline work on pipeline compilation.

Called on: GPUDevice this.

Arguments:

Arguments for the GPUDevice.createReadyRenderPipeline(descriptor) method.

Parameter	Type	Nullable	Optional	Description
descriptor	GPURenderPipelineDescriptor	✘	✘	Description of the GPURenderPipeline to create.

Returns: Promise<GPURenderPipeline>

1. Let promise be a new promise.

2. Issue the following steps on the Device timeline of this:

   1. Let pipeline be a new GPURenderPipeline created as if this.createRenderPipeline() was called with descriptor;

   2. When pipeline is ready to be used, resolve promise with pipeline.

3. Return promise.