Add glCopyCompressedTextureCHROMIUM

gpu/GLES2/extensions/CHROMIUM/CHROMIUM_copy_compressed_texture.txt

+Name
+
+    CHROMIUM_copy_compressed_texture
+
+Name Strings
+
+    GL_CHROMIUM_copy_compressed_texture
+
+Version
+
+    Last Modifed Date: May 28, 2015
+
+Dependencies
+
+    OpenGL ES 2.0 is required.
+
+    GL_AMD_compressed_ATC_texture, GL_ATI_texture_compression_atitc,
+    GL_EXT_texture_compression_dxt1, GL_ANGLE_texture_compression_dxt5,
+    GL_EXT_texture_compression_s3tc and GL_OES_compressed_ETC1_RGB8_texture
+    affects the definition of this extension.
+
+Overview
+
+    This extension provides functionality for copying compressed textures. It
+    adds a new function glCopyCompressedTextureCHROMIUM that works similarily
+    to glCopyTexImage2D, but for compressed textures.

[piman, 2015/05/28 20:34:27]

You mean, similar to glCopyTextureCHROMIUM?
glCopyTexImage2D copies from framebuffer to texture. glCopyTextureCHROMIUM
copies from texture to texture.

[christiank, 2015/06/05 12:53:31]

Yes, maybe that's a better reference. I was thinking that glCopyTexImage2D was a
better reference as glCopyTextureCHROMIUM also respects the pixel storage
modifiers. Anyhow, I'll change the text to "similarily to
glCopyTextureCHROMIUM".

+
+    This extension does not respect pixel-storage modifiers like
+    UNPACK_FLIP_Y_CHROMIUM, GL_UNPACK_PREMULTIPLY_ALPHA_CHROMIUM and
+    GL_UNPACK_UNPREMULTIPLY_ALPHA_CHROMIUM.

[reveman, 2015/05/28 14:06:48]

think that's implicit by not mentioning them.

[christiank, 2015/06/05 12:53:31]

Done.

+
+    Which compressed texture formats that this extension supports depends on
+    the supported texture compression formats of the host GPU.
+
+Issues
+
+    glCopyCompressedTextureCHROMIUM will first try to perform the copy using
+    the GLImage object. If that operation fails glCopyCompressedTextureCHROMIUM
+    will fallback to using glGetCompressedTexImage.

[reveman, 2015/05/28 14:06:48]

I think that's too implementation specific to be mentioned here.

[christiank, 2015/06/05 12:53:31]

Done.

+
+    Depending on platform support, glGetCompressedTexImage may not be
+    available. In that case glCopyCompressedTextureCHROMIUM will return
+    INVALID_OPERATION.

[reveman, 2015/05/28 14:06:48]

Please make sure the requirements to always guarantee that
glCopyCompressedTextureCHROMIUM succeeds are in the Dependencies section. If
this extension is available, then valid usage as described by this spec should
never fail. If the required dependencies are missing, then this extension should
not be available and usage of it should never succeed. 

[christiank, 2015/05/28 14:40:29]

Do you have any suggestion on how I can formally specify that GLImage is
required for OpenGL ES? GLImage is an implementation detail, but is it part of
any feature that I can write as a dependency?

[reveman, 2015/05/28 16:33:08]

I don't think we can have such a dependency. We can depend on CHROMIUM_image but
that doesn't really solve the problem.

[christiank, 2015/06/05 12:53:31]

This should now be addressed since the operation will always succeed, falling
back to copying into a non-compressed texture.

+
+New Procedures and Functions
+
+    The command
+
+        void glCopyCompressedTextureCHROMIUM (GLenum target, GLenum source_id,
+                                              GLenum dest_id,
+                                              GLint internal_format,
+                                              GLenum dest_type,

[piman, 2015/05/28 20:34:27]

What is dest_type? Compressed texture data doesn't have a "type" in the
"format+type" sense that applies to uncompressed data. See
glCompressedTexImage2D.

Do we need to specify internal_format? I'm pretty sure we can't do conversion
(at least not in the general case), so we can just use the internal_format of
the source?

[christiank, 2015/06/05 12:53:31]

It was included because I modeled this function of glCopyTextureChromium. But
you're right, it can be removed.

Fixed.

+                                              GLsizei source_size)

[reveman, 2015/05/28 14:06:48]

glCompressedCopyTextureCHROMIUM? to match the CompressedTexImage naming
convention..

if you rebase this in ToT you'll see that we also need a
CompressedCopySubTextureCHROMIUM as part of this extension.

[christiank, 2015/05/28 14:40:29]

Ahh I see. Should I perhaps rename this document to
CHROMIUM_compressed_copy_texture.txt as well?

[reveman, 2015/05/28 16:33:08]

Sounds good.

[piman, 2015/05/28 20:34:27]

Similarly, I don't think there's a good argument for having source_size here. It
doesn't generally make sense to take a subset of the data, and either way we
have to validate the size against the size passed at glCompressedTexImage2D
time. Since they have to match, might as well omit it.

[christiank, 2015/06/05 12:53:31]

Alright, I'll try to get rid of the source_size parameter. See my discussion in
a different thread.

+
+    Copies the contents of a compressed texture referred to by <source_id> to
+    <dest_id> texture.
+
+    Texture level 0 is copied from the source image to level 0 of the
+    destination texture.
+
+    The internal format of the source and destination texture must be
+    compressed, and they must match. The <internal_format> must be one of the
+    following symbolic constants: GL_ATC_RGB_AMD,
+    GL_ATC_RGBA_INTERPOLATED_ALPHA_AMD, GL_COMPRESSED_RGB_S3TC_DXT1_EXT,
+    GL_COMPRESSED_RGBA_S3TC_DXT5_EXT, GL_ETC1_RGB8_OES
+
+    <target> uses the same parameters as TexImage2D.
+
+    INVALID_OPERATION is generated if the current platform does not support
+    copying compressed textures.

[reveman, 2015/05/28 14:06:48]

I think that should be handled by the availability of this extension instead.

[christiank, 2015/06/05 12:53:31]

Done.

+
+    INVALID_OPERATION is generated if <internal_format> is not one of the valid
+    formats described above.
+
+    INVALID_OPERATION is generated if internal format of source and destination
+    texture doesn't match.
+
+    INVALID_VALUE is generated if <source_id> or <dest_id> are not valid texture
+    objects.
+
+    INVALID_VALUE is generated if textures corresponding to <dest_id> have not
+    been bound as GL_TEXTURE_2D object.
+
+    INVALID_VALUE is generated if level 0 of the source texture is not defined.
+
+Errors
+
+    None.
+
+New Tokens
+
+    None.
+
+New State
+
+    None.
+
+Revision History
+
+    28/5/2015    Documented the extension.