glsl: Add IsCentroid bitfield to gl_fragment_program.

This bitfield tells the back-ends which of a fragment shader's inputs
require centroid interpolation.  It is only set for GLSL fragment
shaders, since assembly fragment shaders don't support centroid
interpolation.

Reviewed-by: Eric Anholt <eric@anholt.net>

src/glsl/ir_set_program_inouts.cpp

@@ -26,7 +26,8 @@
  *
  * Sets the InputsRead and OutputsWritten of Mesa programs.
  *
- * Additionally, for fragment shaders, sets the InterpQualifier array.
+ * Additionally, for fragment shaders, sets the InterpQualifier array and
+ * IsCentroid bitfield.
  *
  * Mesa programs (gl_program, not gl_shader_program) have a set of
  * flags indicating which varyings are read and written.  Computing
@@ -88,6 +89,8 @@ mark(struct gl_program *prog, ir_variable *var, int offset, int len,
             gl_fragment_program *fprog = (gl_fragment_program *) prog;
             fprog->InterpQualifier[var->location + var->index + offset + i] =
                (glsl_interp_qualifier) var->interpolation;
+            if (var->centroid)
+               fprog->IsCentroid |= bitfield;
          }
       } else if (var->mode == ir_var_system_value) {
          prog->SystemValuesRead |= bitfield;
@@ -178,6 +181,7 @@ do_set_program_inouts(exec_list *instructions, struct gl_program *prog,
    if (is_fragment_shader) {
       memset(((gl_fragment_program *) prog)->InterpQualifier, 0,
              sizeof(((gl_fragment_program *) prog)->InterpQualifier));
+      ((gl_fragment_program *) prog)->IsCentroid = 0;
    }
    visit_list_elements(&v, instructions);
 }

src/mesa/main/mtypes.h

@@ -2021,6 +2021,12 @@ struct gl_fragment_program
     * GLSL, the value is INTERP_QUALIFIER_NONE.
     */
    enum glsl_interp_qualifier InterpQualifier[FRAG_ATTRIB_MAX];
+
+   /**
+    * Bitfield indicating, for each fragment shader input, 1 if that input
+    * uses centroid interpolation, 0 otherwise.  Unused inputs are 0.
+    */
+   GLbitfield64 IsCentroid;
 };