[Mesa-dev] Gallium DRI drivers default GL_READ/WRITE_BUFFER to GL_(BACK|FRONT)_LEFT instead of GL_(BACK|FRONT)

[Jose Fonseca]

I wrote a testsuite for apitrace, and one of the tests checks the default GL state against a reference, and it is failing on all Gallium DRI drivers because

{
  parameters: {
    GL_DRAW_BUFFER: "GL_BACK" -> "GL_BACK_LEFT",
    GL_DRAW_BUFFER0: "GL_BACK" -> "GL_BACK_LEFT",
    GL_READ_BUFFER: "GL_BACK" -> "GL_BACK_LEFT",
  },
}

This looks like a bug as glDrawBuffer/glReadBuffer manpages are quite clear: GL_BACK on double buffer visual, GL_

And the odd thing is that Mesa gets it right, but st_visual_to_default_buffer() function goes out of its way to put the wrong values and this fixes it

diff --git a/src/mesa/state_tracker/st_manager.c b/src/mesa/state_tracker/st_manager.c
index d5228d3..c64e175 100644
--- a/src/mesa/state_tracker/st_manager.c
+++ b/src/mesa/state_tracker/st_manager.c
@@ -414,6 +414,8 @@ st_visual_to_default_buffer(const struct st_visual *visual,
    GLenum buf;
    gl_buffer_index idx;
 
+   return;
+
    statt = visual->render_buffer;
    /* do nothing if an invalid render buffer is specified */
    if (statt == ST_ATTACHMENT_INVALID ||


No other DRI driver changes these GL_BACK/GL_FRONT values.

Does this st_visual_to_default_buffer() server any purpose?

If it really does then, then at least GL_(BACK|FRONT)_(LEFT|RIGHT should be replaced with GL_(BACK|FRONT) there.

Jose