gallium: Make TGSI_SEMANTIC_FOG register four-component wide.

D3D9 Shader Model 2 restricted the fog register to one component,
http://msdn.microsoft.com/en-us/library/windows/desktop/bb172945.aspx ,
but that restriction no longer exists in Shader Model 3, and several
WHCK tests enforce that.

So this change:
- lifts the single-component restriction TGSI_SEMANTIC_FOG
  from Gallium interface
- updates the Mesa state tracker to enforce output fog has (f, 0, 0, 1)
- draw module was updated to leave TGSI_SEMANTIC_FOG output registers
  alone

Several gallium drivers that are going out of their way to clear
TGSI_SEMANTIC_FOG components could be simplified in the future.

Thanks to Si Chen and Michal Krol for identifying the problem.

Testing done: piglit fogcoord-*.vpfp tests

Reviewed-by: Roland Scheidegger <[email protected]>

3 files changed, 5 insertions, 19 deletions

diff --git a/src/gallium/auxiliary/draw/draw_llvm.c b/src/gallium/auxiliary/draw/draw_llvm.c
index fe49b8687ab..71cc45f1f68 100644
--- a/src/gallium/auxiliary/draw/draw_llvm.c
+++ b/src/gallium/auxiliary/draw/draw_llvm.c
@@ -659,12 +659,6 @@ generate_vs(struct draw_llvm_variant *variant,
                      LLVMBuildStore(builder, out, outputs[attrib][chan]);
                   }
                   break;
-               case TGSI_SEMANTIC_FOG:
-                  if (chan == 1 || chan == 2)
-                     LLVMBuildStore(builder, bld.zero, outputs[attrib][chan]);
-                  else if (chan == 3)
-                     LLVMBuildStore(builder, bld.one, outputs[attrib][chan]);
-                  break;
                }
             }
          }
diff --git a/src/gallium/auxiliary/draw/draw_vs_exec.c b/src/gallium/auxiliary/draw/draw_vs_exec.c
index 610039498a3..83cc5fda5a7 100644
--- a/src/gallium/auxiliary/draw/draw_vs_exec.c
+++ b/src/gallium/auxiliary/draw/draw_vs_exec.c
@@ -167,12 +167,7 @@ vs_exec_run_linear( struct draw_vertex_shader *shader,
                output[slot][2] = CLAMP(machine->Outputs[slot].xyzw[2].f[j], 0.0f, 1.0f);
                output[slot][3] = CLAMP(machine->Outputs[slot].xyzw[3].f[j], 0.0f, 1.0f);
             }
-            else if (name == TGSI_SEMANTIC_FOG) {
-               output[slot][0] = machine->Outputs[slot].xyzw[0].f[j];
-               output[slot][1] = 0;
-               output[slot][2] = 0;
-               output[slot][3] = 1;
-	    } else
+            else
             {
                output[slot][0] = machine->Outputs[slot].xyzw[0].f[j];
                output[slot][1] = machine->Outputs[slot].xyzw[1].f[j];
diff --git a/src/gallium/docs/source/tgsi.rst b/src/gallium/docs/source/tgsi.rst
index f80c08d3175..0501aca54fc 100644
--- a/src/gallium/docs/source/tgsi.rst
+++ b/src/gallium/docs/source/tgsi.rst
@@ -2420,13 +2420,10 @@ TGSI_SEMANTIC_FOG
 
 Vertex shader inputs and outputs and fragment shader inputs may be
 labeled with TGSI_SEMANTIC_FOG to indicate that the register contains
-a fog coordinate in the form (F, 0, 0, 1).  Typically, the fragment
-shader will use the fog coordinate to compute a fog blend factor which
-is used to blend the normal fragment color with a constant fog color.
-
-Only the first component matters when writing from the vertex shader;
-the driver will ensure that the coordinate is in this format when used
-as a fragment shader input.
+a fog coordinate.  Typically, the fragment shader will use the fog coordinate
+to compute a fog blend factor which is used to blend the normal fragment color
+with a constant fog color.  But fog coord really is just an ordinary vec4
+register like regular semantics.
 
 
 TGSI_SEMANTIC_PSIZE