[Mesa-dev] [PATCH] i965: Set brw_wm_prog_key::alpha_test only if nr_color_buffers == 0.

[Kenneth Graunke]

If alpha testing is enabled, we need to include alpha in the FB write.
Normally, this occurs as part of a color buffer write, but it's possible
to use alpha testing without any color buffers.  The alpha_test flag
lets brw_fs.cpp know that the shader needs to send alpha anyway.

Since the flag's only use occurs when nr_color_buffers == 0, we don't
need to set it in the general case; in fact, doing so will result in two
indentical shaders being compiled, wasting time and program cache space.

This patch also renames it to "alpha_only", since it no longer
represents when alpha testing is enabled or disabled.

Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
---
 src/mesa/drivers/dri/i965/brw_fs_visitor.cpp |    2 +-
 src/mesa/drivers/dri/i965/brw_wm.c           |    7 ++++---
 src/mesa/drivers/dri/i965/brw_wm.h           |    2 +-
 3 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
index 4f27a81..3db346c 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
@@ -2193,7 +2193,7 @@ fs_visitor::emit_fb_writes()
    }
 
    if (c->key.nr_color_regions == 0) {
-      if (c->key.alpha_test) {
+      if (c->key.alpha_only) {
 	 /* If the alpha test is enabled but there's no color buffer,
 	  * we still need to send alpha out the pipeline to our null
 	  * renderbuffer.
diff --git a/src/mesa/drivers/dri/i965/brw_wm.c b/src/mesa/drivers/dri/i965/brw_wm.c
index a169fd5..10f1dce 100644
--- a/src/mesa/drivers/dri/i965/brw_wm.c
+++ b/src/mesa/drivers/dri/i965/brw_wm.c
@@ -431,10 +431,8 @@ static void brw_wm_populate_key( struct brw_context *brw,
 
    /* Build the index for table lookup
     */
-   /* _NEW_COLOR */
-   key->alpha_test = ctx->Color.AlphaEnabled;
-
    if (intel->gen < 6) {
+      /* _NEW_COLOR */
       if (fp->program.UsesKill || ctx->Color.AlphaEnabled)
 	 lookup |= IZ_PS_KILL_ALPHATEST_BIT;
 
@@ -529,6 +527,9 @@ static void brw_wm_populate_key( struct brw_context *brw,
    /* _NEW_BUFFERS */
    key->nr_color_regions = ctx->DrawBuffer->_NumColorDrawBuffers;
 
+   /* _NEW_COLOR */
+   key->alpha_only = ctx->Color.AlphaEnabled && key->nr_color_regions == 0;
+
    /* CACHE_NEW_VS_PROG */
    key->vp_outputs_written = brw->vs.prog_data->outputs_written;
 
diff --git a/src/mesa/drivers/dri/i965/brw_wm.h b/src/mesa/drivers/dri/i965/brw_wm.h
index 8f1cb8c..88f21d0 100644
--- a/src/mesa/drivers/dri/i965/brw_wm.h
+++ b/src/mesa/drivers/dri/i965/brw_wm.h
@@ -65,7 +65,7 @@ struct brw_wm_prog_key {
    GLuint flat_shade:1;
    GLuint nr_color_regions:5;
    GLuint render_to_fbo:1;
-   GLuint alpha_test:1;
+   GLuint alpha_only:1; /**< No color regions, but alpha testing enabled */
    GLuint clamp_fragment_color:1;
    GLuint line_aa:2;
 
-- 
1.7.10.4