GL Implementation for GPU Discardable

gpu/GLES2/extensions/CHROMIUM/CHROMIUM_discardable_texture.txt

+Name
+
+    CHROMIUM_discardable_texture
+
+Name Strings
+
+    GL_CHROMIUM_discardable_texture
+
+Version
+
+    Last Modified Date: April 11, 2017
+
+Dependencies
+
+    OpenGL ES 2.0 is required.
+
+Overview
+
+    This extension defines a way to mark textures as "unlocked" or "not
+    currently in use", giving GL the opportunity to delete these textures as
+    needed (potentially in cases of memory pressure). Clients may try to
+    re-lock such a texture, and if successful may continue to use the texture
+    as normal.
+
+    This allows a client to opportunistically cache data for future use,
+    without worrying about exact memory limits.
+
+New Procedures and Functions
+
+    void glInitializeDiscardableTextureCHROMIUM (GLuint texture_id);
+
+    Notifies GL that a texture may be unlocked in the future. Must be called
+    once on a texture, before any uses of glUnlockTextureCHROMIUM. Will set
+    GL_INVALID_VALUE if called with a texture ID that does not exist, or if
+    called with a texture ID that has already been initialized.
+
+    void glUnlockTextureCHROMIUM (GLuint texture_id);
+
+    Notifies GL that a texture is no longer in use. Once a client calls
+    glUnlockTextureCHROMIUM, they may not use the indicated texture in any
+    future GL calls. This includes using the texture indirectly, via objects
+    (FBOs, etc...) that refer to the texture. Using a texture once it has
+    been unlocked is undefined, and may behave as though the texture has been
+    deleted. Will set GL_INVALID_VALUE if called with a texture ID that has
+    not beein initialized via glInitializeDiscardableTextureCHROMIUM.
+
+    bool glLockTextureCHROMIUM (GLuint texture_id);
+
+    Requests that GL re-lock the indicated texture, allowing it to be used in
+    future operations. If this function returns true, the client may continue
+    to use the indicated texture as though it was never unlocked. If this
+    function returns false, the client may not use the texture again, and
+    should behave as if the texture was deleted via glDeleteTextures. Will
+    set GL_INVALID_VALUE if called with a texture ID that has not beein
+    initialized via glInitializeDiscardableTextureCHROMIUM.
+
+New Tokens
+
+    None.
+
+Errors
+
+    None.
+
+New State
+
+    None.
+
+Revision History
+
+    3/11/2017  Documented the extension