i965/msaa: Add sample-alpha-to-coverage support for multiple render targets

Render Target Write message should include source zero alpha value when
sample-alpha-to-coverage is enabled for an FBO with  multiple render targets.
Source zero alpha value is used as fragment coverage for all the render
targets.

This patch makes piglit tests draw-buffers-alpha-to-coverage and
alpha-to-coverage-no-draw-buffer-zero to pass on Sandybridge. No
regressions are observed with piglit all.tests.

V2: Revert all the changes made in emit_color_write() function to
include src0 alpha for targets > 0. Now handling this case in a if
block.

V3: Correctly calculate the instruction length for buffer zero.
Properly handle the case of dual_src_blend when alpha-to-coverage
is enabled.

Signed-off-by: Anuj Phogat <[email protected]>
Reviewed-by: Paul Berry <[email protected]>

1 files changed, 1 insertions, 0 deletions

diff --git a/src/mesa/drivers/dri/i965/brw_wm.h b/src/mesa/drivers/dri/i965/brw_wm.h
index 53b644fa002..5e4af2781ea 100644
--- a/src/mesa/drivers/dri/i965/brw_wm.h
+++ b/src/mesa/drivers/dri/i965/brw_wm.h
@@ -64,6 +64,7 @@ struct brw_wm_prog_key {
    GLuint stats_wm:1;
    GLuint flat_shade:1;
    GLuint nr_color_regions:5;
+   GLuint sample_alpha_to_coverage:1; /* _NEW_MULTISAMPLE */
    GLuint render_to_fbo:1;
    GLuint clamp_fragment_color:1;
    GLuint line_aa:2;