r300g: fix alpha-test with no colorbuffer

Piglit:
- fbo-alphatest-nocolor

NOTE: This is a candidate for the stable branches.
(cherry picked from commit 226ae9d6c8f282de788404b4d98af7ddf8ee30f4)

1 files changed, 5 insertions, 0 deletions

diff --git a/src/gallium/drivers/r300/r300_emit.c b/src/gallium/drivers/r300/r300_emit.c
index b2b34c3efc..6d2543727a 100644
--- a/src/gallium/drivers/r300/r300_emit.c
+++ b/src/gallium/drivers/r300/r300_emit.c
@@ -475,6 +475,11 @@ void r300_emit_fb_state_pipelined(struct r300_context *r300,
     for (i = 0; i < fb->nr_cbufs; i++) {
         OUT_CS(r300_surface(fb->cbufs[i])->format);
     }
+    for (; i < 1; i++) {
+        OUT_CS(R300_US_OUT_FMT_C4_8 |
+               R300_C0_SEL_B | R300_C1_SEL_G |
+               R300_C2_SEL_R | R300_C3_SEL_A);
+    }
     for (; i < 4; i++) {
         OUT_CS(R300_US_OUT_FMT_UNUSED);
     }