gpu: introduce glCopySubTextureCHROMIUM

gpu/GLES2/extensions/CHROMIUM/CHROMIUM_copy_texture.txt

Index: gpu/GLES2/extensions/CHROMIUM/CHROMIUM_copy_texture.txt
diff --git a/gpu/GLES2/extensions/CHROMIUM/CHROMIUM_copy_texture.txt b/gpu/GLES2/extensions/CHROMIUM/CHROMIUM_copy_texture.txt
index ad9ca689ca90303ffa3c9342e3d70894ef7a5719..27ead406233bbe55cb63b19293386fadf8883ff3 100644
--- a/gpu/GLES2/extensions/CHROMIUM/CHROMIUM_copy_texture.txt
+++ b/gpu/GLES2/extensions/CHROMIUM/CHROMIUM_copy_texture.txt
@@ -36,9 +36,11 @@ Overview
 
 New Procedures and Functions
 
-    void glCopyTextureCHROMIUM (GLenum target, GLenum source_id,
-                                GLenum dest_id, GLint level,
-                                GLint internal_format, GLenum dest_type)
+    The command
+
+        void glCopyTextureCHROMIUM (GLenum target, GLenum source_id,
+                                    GLenum dest_id, GLint level,
+                                    GLint internal_format, GLenum dest_type)
 
     Copies the contents of texture referred to by <source_id> to texture
     <dest_id>.
@@ -90,6 +92,39 @@ New Procedures and Functions
     INVALID_VALUE is generated if <level> is not a valid level of the
     destination texture, or if level 0 of the source texture is not defined.
 
+    The command
+
+        void glCopySubTextureCHROMIUM (GLenum target, GLenum source_id,
+                                       GLenum dest_id, GLint level,
+                                       GLint xoffset, GLint yoffset)
+
+    Copies the sub contents of texture referred to by <source_id> to texture
+    <dest_id>.

[Ken Russell (switch to Gerrit), 2015/01/24 01:33:24]

Please expand upon this sentence and say exactly what it does to the texture
|dest_id|. glCopyTextureCHROMIUM is ambiguous about this; it's worth expanding
its documentation to say that it reallocates the destination texture to be the
same size as the source texture.

This function's documentation should explicitly say that it copies the contents
of the texture |source_id| to a location in the texture |dest_id| without
reallocating the destination texture.

[dshwang, 2015/02/10 18:11:55]

Yes, I explicitly explain this for glCopyTextureCHROMIUM
Yes, I explicitly explain this also.

+
+    See CopyTextureCHROMIUM for the interpretation of the <target> and <level>
+    arguments.

[Ken Russell (switch to Gerrit), 2015/01/24 01:33:24]

Are you going to generalize the CopySubTexture variant to handle level > 0? The
code handles it. If so then please don't refer to CopyTextureCHROMIUM for the
level argument, but define its semantics here.

[dshwang, 2015/02/10 18:11:55]

level > 0 will never be supported because glFramebufferTexture2D doesn't support
level > 0. CopyTextureCHROMIUM implementation requires <dest_id> texture bound
to FBO.
https://www.khronos.org/opengles/sdk/docs/man/xhtml/glFramebufferTexture2D.xml

+
+    <xoffset> and <yoffset> specify a texel offset in the x and y direction
+    respectively within the destination texture.
+
+    INVALID_OPERATION is generated if source internal_format and destination
+    internal_format are not one of the valid formats described above.
+
+    INVALID_VALUE is generated if <target> is not GL_TEXTURE_2D.
+
+    INVALID_OPERATION is generated if the destination texture has not been
+    defined.
+
+    INVALID_VALUE is generated if <level> is less than 0.
+
+    INVALID_VALUE may be generated if <level> >log2(max), where max is
+    the returned value of GL_MAX_TEXTURE_SIZE.
+
+    INVALID_VALUE is generated if <xoffset> < 0 , or <yoffset> < 0.
+
+    INVALID_VALUE is generated if (<xoffset> + source_width) > dest_width,
+    or (<yoffset> + source_height) > dest_height.
+
 Errors
 
     None.