From: Eric Anholt <eric@anholt.net>
Date: Wed, 11 May 2011 21:07:44 +0000 (-0700)
Subject: i965/gen6: Fix blending state when no color buffer is bound.
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=367020d87ce8c27aeb58b3887fbd29d216fdc151;p=mesa.git

i965/gen6: Fix blending state when no color buffer is bound.

This is part of fixing fbo-alphatest-nocolor -- a regression in
35e8fe5c99b285f348cb8a1bba2931f120f7c0a1 after the initial regression,
that had us using a garbage BLEND_STATE[0] (in particular, the alpha
test enable) if no color buffer was bound.
---

diff --git a/src/mesa/drivers/dri/i965/gen6_cc.c b/src/mesa/drivers/dri/i965/gen6_cc.c
index 66357f00fa6..2b16d6cdc01 100644
--- a/src/mesa/drivers/dri/i965/gen6_cc.c
+++ b/src/mesa/drivers/dri/i965/gen6_cc.c
@@ -39,8 +39,18 @@ prepare_blend_state(struct brw_context *brw)
    struct gen6_blend_state *blend;
    int b;
    int nr_draw_buffers = ctx->DrawBuffer->_NumColorDrawBuffers;
-   int size = sizeof(*blend) * nr_draw_buffers;
-
+   int size;
+
+   /* We need at least one BLEND_STATE written, because we might do
+    * thread dispatch even if _NumColorDrawBuffers is 0 (for example
+    * for computed depth or alpha test), which will do an FB write
+    * with render target 0, which will reference BLEND_STATE[0] for
+    * alpha test enable.
+    */
+   if (nr_draw_buffers == 0 && ctx->Color.AlphaEnabled)
+      nr_draw_buffers = 1;
+
+   size = sizeof(*blend) * nr_draw_buffers;
    blend = brw_state_batch(brw, size, 64, &brw->cc.blend_state_offset);
 
    memset(blend, 0, size);