[Mesa-dev] [PATCH 2/3] st/glsl_to_tgsi: swizzle PROGRAM_OUTPUTs correctly in src_register translation

[Nicolai Hähnle]

From: Nicolai Hähnle <nicolai.haehnle at amd.com>

This is required for reading directly from fragment shader stencil and depth
outputs.
---
 src/mesa/state_tracker/st_glsl_to_tgsi.cpp | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/src/mesa/state_tracker/st_glsl_to_tgsi.cpp b/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
index 978dc46..8a247ea 100644
--- a/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
+++ b/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
@@ -5376,23 +5376,33 @@ src_register(struct st_translate *t, const st_src_reg *reg)
 {
    int index = reg->index;
    int double_reg2 = reg->double_reg2 ? 1 : 0;
 
    switch(reg->file) {
    case PROGRAM_UNDEFINED:
       return ureg_imm4f(t->ureg, 0, 0, 0, 0);
 
    case PROGRAM_TEMPORARY:
    case PROGRAM_ARRAY:
-   case PROGRAM_OUTPUT:
       return ureg_src(dst_register(t, reg->file, reg->index, reg->array_id));
 
+   case PROGRAM_OUTPUT: {
+      struct ureg_dst dst = dst_register(t, reg->file, reg->index, reg->array_id);
+      assert(dst.WriteMask != 0);
+      unsigned shift = ffs(dst.WriteMask) - 1;
+      return ureg_swizzle(ureg_src(dst),
+                          shift,
+                          MIN2(shift + 1, 3),
+                          MIN2(shift + 2, 3),
+                          MIN2(shift + 3, 3));
+   }
+
    case PROGRAM_UNIFORM:
       assert(reg->index >= 0);
       return reg->index < t->num_constants ?
                t->constants[reg->index] : ureg_imm4f(t->ureg, 0, 0, 0, 0);
    case PROGRAM_STATE_VAR:
    case PROGRAM_CONSTANT:       /* ie, immediate */
       if (reg->has_index2)
          return ureg_src_register(TGSI_FILE_CONSTANT, reg->index);
       else
          return reg->index >= 0 && reg->index < t->num_constants ?
-- 
2.7.4