i915g: Fix the blending for the A8 destination buffer case.

The i915 GPU can't do A8 dst, so we abuse GREEN8 buffers for that
purpose. However, things get hairy as we start to do blending,
because then GL_DST_*_ALPHA should be replaced with GL_DST_*_COLOR.
This is what we do here.

Fixes piglt fbo-alpha.

1 files changed, 23 insertions, 6 deletions

diff --git a/src/gallium/drivers/i915/i915_state_emit.c b/src/gallium/drivers/i915/i915_state_emit.c
index 426c683502a..9d487cfcdc1 100644
--- a/src/gallium/drivers/i915/i915_state_emit.c
+++ b/src/gallium/drivers/i915/i915_state_emit.c
@@ -151,8 +151,25 @@ emit_immediate(struct i915_context *i915)
    }
 
    for (i = 1; i < I915_MAX_IMMEDIATE; i++) {
-      if (dirty & (1 << i))
-         OUT_BATCH(i915->current.immediate[i]);
+      if (dirty & (1 << i)) {
+         /* Fixup blend function for A8 dst buffers.
+          * When we blend to an A8 buffer, the GPU thinks it's a G8 buffer,
+          * and therefore we need to use the color factor for alphas. */
+         if ((i == I915_IMMEDIATE_S6) &&
+             (i915->current.target_fixup_format == PIPE_FORMAT_A8_UNORM)) {
+            uint32_t imm = i915->current.immediate[i];
+            uint32_t srcRGB = (imm >> S6_CBUF_SRC_BLEND_FACT_SHIFT) & BLENDFACT_MASK;
+            if (srcRGB == BLENDFACT_DST_ALPHA)
+               srcRGB = BLENDFACT_DST_COLR;
+            else if (srcRGB == BLENDFACT_INV_DST_ALPHA)
+               srcRGB = BLENDFACT_INV_DST_COLR;
+            imm &= ~SRC_BLND_FACT(BLENDFACT_MASK);
+            imm |= SRC_BLND_FACT(srcRGB);
+            OUT_BATCH(imm);
+         } else {
+            OUT_BATCH(i915->current.immediate[i]);
+         }
+      }
    }
 }
 
@@ -346,7 +363,7 @@ emit_constants(struct i915_context *i915)
 static void
 validate_program(struct i915_context *i915, unsigned *batch_space)
 {
-   uint additional_size = i915->current.need_target_fixup;
+   uint additional_size = i915->current.target_fixup_format ? 1 : 0;
 
    /* we need more batch space if we want to emulate rgba framebuffers */
    *batch_space = i915->fs->program_len + 3 * additional_size;
@@ -355,7 +372,7 @@ validate_program(struct i915_context *i915, unsigned *batch_space)
 static void
 emit_program(struct i915_context *i915)
 {
-   uint target_fixup = i915->current.need_target_fixup;
+   uint need_target_fixup = i915->current.target_fixup_format ? 1 : 0;
    uint i;
 
    /* we should always have, at least, a pass-through program */
@@ -364,7 +381,7 @@ emit_program(struct i915_context *i915)
    {
       /* first word has the size, we have to adjust that */
       uint size = (i915->fs->program[0]);
-      size += target_fixup * 3;
+      size += need_target_fixup * 3;
       OUT_BATCH(size);
    }
 
@@ -373,7 +390,7 @@ emit_program(struct i915_context *i915)
       OUT_BATCH(i915->fs->program[i]);
 
    /* we emit an additional mov with swizzle to fake RGBA framebuffers */
-   if (target_fixup) {
+   if (need_target_fixup) {
       /* mov out_color, out_color.zyxw */
       OUT_BATCH(A0_MOV |
                 (REG_TYPE_OC << A0_DEST_TYPE_SHIFT) |