dawn-cmake/docs/dawn/features/dawn_internal_usages.md
Ben Clayton 26c31f6b2c Shuffle 'docs' directories
As part of the tint -> dawn merge.

Bug: dawn:1275
Change-Id: Ice0c9d2f03f6d7e96471cf8398aecd16273c833f
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/78400
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Ben Clayton <bclayton@google.com>
2022-01-27 18:33:47 +00:00

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# Dawn Internal Usages
The `dawn-internal-usages` feature allows adding additional usage which affects how a texture is allocated, but does not affect normal frontend validation.
Adds `WGPUDawnTextureInternalUsageDescriptor` for specifying additional internal usages to create a texture with.
Example Usage:
```
wgpu::DawnTextureInternalUsageDescriptor internalDesc = {};
internalDesc.internalUsage = wgpu::TextureUsage::CopySrc;
wgpu::TextureDescriptor desc = {};
// set properties of desc.
desc.nextInChain = &internalDesc;
device.CreateTexture(&desc);
```
Adds `WGPUDawnEncoderInternalUsageDescriptor` which may be chained on `WGPUCommandEncoderDescriptor`. Setting `WGPUDawnEncoderInternalUsageDescriptor::useInternalUsages` to `true` means that internal resource usages will be visible during validation. ex.) A texture that has `WGPUTextureUsage_CopySrc` in `WGPUDawnEncoderInternalUsageDescriptor::internalUsage`, but not in `WGPUTextureDescriptor::usage` may be used as the source of a copy command.
Example Usage:
```
wgpu::DawnEncoderInternalUsageDescriptor internalEncoderDesc = { true };
wgpu::CommandEncoderDescriptor encoderDesc = {};
encoderDesc.nextInChain = &internalEncoderDesc;
wgpu::CommandEncoder encoder = device.CreateCommandEncoder(&encoderDesc);
// This will be valid
wgpu::ImageCopyTexture src = {};
src.texture = texture;
encoder.CopyTextureToBuffer(&src, ...);
```
One use case for this is so that Chromium can use an internal copyTextureToTexture command to implement copies from a WebGPU texture-backed canvas to other Web platform primitives when the swapchain texture was not explicitly created with CopySrc usage in Javascript.
Note: copyTextureToTextureInternal will be removed in favor of `WGPUDawnEncoderInternalUsageDescriptor`.