cogl-atlas: Try 4 different approaches for migrating textures

Instead of directly banging GL to migrate textures the atlas now uses
the CoglFramebuffer API. It will use one of four approaches; it can
set up two FBOs and use _cogl_blit_framebuffer to copy between them;
it can use a single target fbo and then render the source texture to
the FBO using a Cogl draw call; it can use a single FBO and call
glCopyTexSubImage2D; or it can fallback to reading all of the texture
data back to system memory and uploading it again with a sub texture
update.

Previously GL calls were used directly because Cogl wasn't able to
create a framebuffer without a stencil and depth buffer. However there
is now an internal version of cogl_offscreen_new_to_texture which
takes a set of flags to disable the two buffers.

The code for blitting has now been moved into a separate file called
cogl-blit.c because it has become quite long and it may be useful
outside of the atlas at some point.

The 4 different methods have a fixed order of preference which is:

* Texture render between two FBOs
* glBlitFramebuffer
* glCopyTexSubImage2D
* glGetTexImage + glTexSubImage2D

Once a method is succesfully used it is tried first for all subsequent
blits. The default default can be overridden by setting the
environment variable COGL_ATLAS_DEFAULT_BLIT_MODE to one of the
following values:

* texture-render
* framebuffer
* copy-tex-sub-image
* get-tex-data

1 files changed, 1 insertions, 0 deletions

diff --git a/cogl/cogl-context.h b/cogl/cogl-context.h
index 8c0161fa..eead5dc0 100644
--- a/cogl/cogl-context.h
+++ b/cogl/cogl-context.h
@@ -175,6 +175,7 @@ typedef struct
   gboolean          in_begin_gl_block;
 
   CoglPipeline     *texture_download_pipeline;
+  CoglPipeline     *blit_texture_pipeline;
 
   GSList           *atlases;