kc3-lang/angle/src/libANGLE/renderer/metal/doc/TextureDataCompleteness.md

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• Hash : 53e45360
  Author :
  Date : 2019-11-09T17:26:58
  

  Metal: support texture's incomplete image definitions.
  
  glTexImage*, glCopyImage* will copy data to the image at the respective
  index, then during draw call, the image data will be transferred to
  real Metal texture.
  
  Test done: MipmapTest.DefineValidExtraLevelAndUseItLater
  
  For implementation notes, see
  src/libANGLE/renderer/metal/doc/TextureDataCompleteness.md
  
  Bug: angleproject:2634
  Change-Id: I0ca24c8beff2e109a794260c436985e9f4650d83
  Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1906609
  Commit-Queue: Jamie Madill <jmadill@chromium.org>
  Reviewed-by: Jamie Madill <jmadill@chromium.org>
  

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• src/libANGLE/renderer/metal/doc/TextureDataCompleteness.md

• # Texture data completeness's handling in the Metal back-end
  
  The OpenGL spec allows a texture's images to be defined without consistent size and format through
  glTexImage*, glCopyImage* calls. The texture doesn't need to be complete when created.
  
  The OpenGL context checks the texture's images during draw calls. It considers the texture complete
  if the images are consistent in size and format. Then it uses the texture for rendering.
  
  Metal textures (i.e. MTLTexture) on the other hand require consistent defined images at all times.
  MTLTextures are always created complete.
  
  This is an overview of how the Metal back-end implements images' management for a texture to make
  sure it is GL spec conformant (TextureMtl):
  1. Initially:
      * no actual MTLTexture is created yet.
      * glTexImage/glCopyImage(slice,level):
        * a single image (`images[slice][level]`: 2D/3D MTLTexture no mipmap + single slice) is
          created to store data for the texture at this level/slice.
      * glTexSubImage/glCopyTexSubImage(slice,level):
        * modifies the data of `images[slice][level]`;
  2. If the texture is complete at Draw/generateMip/FBO attachment call:
      * an actual MTLTexture object is created. We can call it "native" texture, i.e. the real texture
        that will be consumed by Metal draw calls.
        - `images[0][0]` --> copy to actual texture's slice 0, level 0.
        - `images[0][1]` --> copy to actual texture's slice 0, level 1.
        - `images[0][2]` --> copy to actual texture's slice 0, level 2.
        - ...
      * The images will be destroyed, then re-created to become texture views of the actual texture at
        the specified level/slice.
        - `images[0][0]` -> view of actual texture's slice 0, level 0.
        - `images[0][1]` -> view of actual texture's slice 0, level 1.
        - `images[0][2]` -> view of actual texture's slice 0, level 2.
        - ...
  3. After texture is complete:
      * glTexSubImage/glCopyTexSubImage(slice,level):
        * `images[slice][level]`'s content is modified, which means the actual texture's content at
          respective slice & level is modified also. Since the former is a view of the latter at given
          slice & level.
      * glTexImage/glCopyImage(slice,level):
        * If size != `images[slice][level]`.size():
          - Destroy the actual texture (the other views are kept intact), recreate
            `images[slice][level]` as single image same as initial stage. The other views are kept
            intact so that texture data at those slice & level can be reused later.
        * else:
          - behaves as glTexSubImage/glCopyTexSubImage(slice,level).
  

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