mesa: avoid generating constant vertex attributes in fixedfunc programs

Keep track of enabled/active vertex attributes.
Keep track of potential vertex program outputs.

When generating fragment program, replace references to fragment attributes
which are effectively non-varying and non-computed passthrough attributes with
references to the new CURRENT_ATTRIB tracked state value.

Only downside is slight ugliness in VBO code where we need to validate state
twice in succession.

src/mesa/main/state.c

@@ -465,7 +465,8 @@ _mesa_update_state_locked( GLcontext *ctx )
       _mesa_update_tnl_spaces( ctx, new_state );
 
    if (ctx->FragmentProgram._MaintainTexEnvProgram) {
-      prog_flags |= (_NEW_TEXTURE | _NEW_FOG | _DD_NEW_SEPARATE_SPECULAR);
+      prog_flags |= (_NEW_ARRAY | _NEW_TEXTURE_MATRIX | _NEW_LIGHT |
+                     _NEW_TEXTURE | _NEW_FOG | _DD_NEW_SEPARATE_SPECULAR);
    }
    if (ctx->VertexProgram._MaintainTnlProgram) {
       prog_flags |= (_NEW_ARRAY | _NEW_TEXTURE | _NEW_TEXTURE_MATRIX |
@@ -504,3 +505,38 @@ _mesa_update_state( GLcontext *ctx )
    _mesa_update_state_locked(ctx);
    _mesa_unlock_context_textures(ctx);
 }
+
+
+
+
+/* Want to figure out which fragment program inputs are actually
+ * constant/current values from ctx->Current.  These should be
+ * referenced as a tracked state variable rather than a fragment
+ * program input, to save the overhead of putting a constant value in
+ * every submitted vertex, transferring it to hardware, interpolating
+ * it across the triangle, etc...
+ *
+ * When there is a VP bound, just use vp->outputs.  But when we're
+ * generating vp from fixed function state, basically want to
+ * calculate:
+ *
+ * vp_out_2_fp_in( vp_in_2_vp_out( varying_inputs ) | 
+ *                 potential_vp_outputs )
+ *
+ * Where potential_vp_outputs is calculated by looking at enabled
+ * texgen, etc.
+ * 
+ * The generated fragment program should then only declare inputs that
+ * may vary or otherwise differ from the ctx->Current values.
+ * Otherwise, the fp should track them as state values instead.
+ */
+void
+_mesa_set_varying_vp_inputs( GLcontext *ctx,
+                             unsigned varying_inputs )
+{
+   if (ctx->varying_vp_inputs != varying_inputs) {
+      ctx->varying_vp_inputs = varying_inputs;
+      ctx->NewState |= _NEW_ARRAY;
+      //_mesa_printf("%s %x\n", __FUNCTION__, varying_inputs);
+   }
+}