Skip to content

ImageBitmapToTexture.md

Latest commit

 

History

History
39 lines (31 loc) · 2.72 KB

ImageBitmapToTexture.md

File metadata and controls

39 lines (31 loc) · 2.72 KB

WebGPU + ImageBitmap

dictionary GPUImageBitmapCopyView {
    required ImageBitmap imageBitmap;
    GPUOrigin2D origin;
};

partial interface GPUQueue {
    void copyImageBitmapToTexture(
        GPUImageBitmapCopyView source,
        GPUTextureCopyView destination,
        // For now, copySize.z must be 1.
        GPUExtent3D copySize);
};

copyImageBitmapToTexture submits a copy from a source sub-rectangle of an ImageBitmap into a destination sub-resource of a GPUTexture. The ImageBitmap must not be detached, if it is, a validation error is generated.

Alternatives Considered

  • Creating a GPUTexture directly from an ImageBitmap, attempting to avoid copies, is impractical because it requires the GPUTexture's format to match the internal representation of the ImageBitmap, which is not exposed to the Web platform. Additionally, ImageBitmaps may be GPU- or CPU-backed, and wrapping a CPU-backed ImageBitmap is a significant meta-operation that requires an additional copy to be submitted.
  • Having copyImageBitmapToTexture on GPUCommandEncoder: this makes implementations much more complicated because they can't know when the copy will be effectively submitted. It also allows having multiple copyImageBitmapToTexture at different sports in the GPUCommandEncoder which would require splicing the encoder and keeping track of all the chunks. Realistically, copying ImageBitmaps will be during loading to copy from <img> elements, or at most a couple times per frame for example to copy a camera frame, so an immediate copy is fine.

Issues

  • Some of the ImageBitmap creation options, such as "flipY", have semantics that have to match the target graphics API where the data is intended to be used. For WebGL, imageOrientation: "flipY" is necessary to ensure that the resulting WebGLTexture is oriented correctly. For WebGPU, it may be the case that texture origins are defined differently from WebGL, necessitating imageOrientation: "none". These cases will have to be thoroughly tested.

  • The browser may choose an internal representation for an ImageBitmap which is not ideal for usage by WebGPU (or, for that matter, by WebGL). This could result in texture uploads being significantly more expensive than necessary due to per-pixel data swizzling during upload. Providing any hint about the intended usage of the ImageBitmap during its construction (for example "for use with WebGL" or "for use with this WebGPU adapter") would require changes to the HTML specification. Attempts to change Chrome's internal representation of ImageBitmap have not yet been successful; it's not clear how feasible it would be in other browsers.