shader: on GLES replace FS COLOR inputs that are not availabe by constants

Legacy FS shaders may use glColor and glSecondaryColor without the VS
actually emitting it. However, on GLES the interfaces between stages must
be matched, so replace FS input colors with a constant when they are not
emitted by the VS.

v2: - revert how the color_in_mask is populated
    - handle back color too
    - correctly appply the interface matching only on GLES (Bug reported
      by David Riley).

Signed-off-by: Gert Wollny <gert.wollny@collabora.com>
Reviewed-by: John Bates <jbates@chromium.org>

src/vrend_renderer.c

@@ -3417,6 +3417,9 @@ static inline void vrend_sync_shader_io(struct vrend_sub_context *sub_ctx,
 
       key->num_in_clip = sub_ctx->shaders[prev_type]->current->var_sinfo.num_out_clip;
       key->num_in_cull = sub_ctx->shaders[prev_type]->current->var_sinfo.num_out_cull;
+
+      if (vrend_state.use_gles && type == PIPE_SHADER_FRAGMENT)
+         key->fs.available_color_in_bits = sub_ctx->shaders[prev_type]->current->var_sinfo.legacy_color_bits;
    }
 
    int next_type = -1;

src/vrend_shader.c

@@ -261,6 +261,7 @@ struct dump_ctx {
    int fs_uses_clipdist_input;
    int glsl_ver_required;
    int color_in_mask;
+   int color_out_mask;
    /* only used when cull is enabled */
    uint8_t num_cull_dist_prop, num_clip_dist_prop;
    bool has_pervertex;
@@ -1409,8 +1410,10 @@ iter_declaration(struct tgsi_iterate_context *iter,
                   name_prefix = "gl_FrontColor";
                else if (ctx->outputs[i].sid == 1)
                   name_prefix = "gl_FrontSecondaryColor";
-            } else
+            } else {
                name_prefix = ctx->is_last_vertex_stage ? "ex" : get_stage_output_name_prefix(iter->processor.Processor);
+               ctx->color_out_mask |= (1 << decl->Semantic.Index);
+            }
          }
          ctx->outputs[i].override_no_wm = false;
          break;
@@ -1424,9 +1427,10 @@ iter_declaration(struct tgsi_iterate_context *iter,
                else if (ctx->outputs[i].sid == 1)
                   name_prefix = "gl_BackSecondaryColor";
                break;
-            } else
+            } else {
-               name_prefix = "ex";
+               ctx->outputs[i].override_no_wm = false;
-            ctx->outputs[i].override_no_wm = false;
+               ctx->color_out_mask |= (1 << decl->Semantic.Index) << 2;
+            }
             break;
          }
          /* fallthrough */
@@ -6581,6 +6585,24 @@ static void emit_ios_fs(const struct dump_ctx *ctx,
          const char *prefix = "";
          const char *auxprefix = "";
 
+         if (ctx->cfg->use_gles) {
+            if (ctx->inputs[i].name == TGSI_SEMANTIC_COLOR) {
+               if (!(ctx->key->fs.available_color_in_bits & (1 << ctx->inputs[i].sid))) {
+                  emit_hdrf(glsl_strbufs, "vec4 %s = vec4(0.0, 0.0, 0.0, 0.0);\n",
+                            ctx->inputs[i].glsl_name);
+                  continue;
+               }
+            }
+
+            if (ctx->inputs[i].name == TGSI_SEMANTIC_BCOLOR) {
+               if (!(ctx->key->fs.available_color_in_bits & (1 << ctx->inputs[i].sid) << 2)) {
+                  emit_hdrf(glsl_strbufs, "vec4 %s = vec4(0.0, 0.0, 0.0, 0.0);\n",
+                            ctx->inputs[i].glsl_name);
+                  continue;
+               }
+            }
+         }
+
          if (ctx->inputs[i].name == TGSI_SEMANTIC_GENERIC ||
               ctx->inputs[i].name == TGSI_SEMANTIC_COLOR ||
               ctx->inputs[i].name == TGSI_SEMANTIC_BCOLOR) {
@@ -7092,6 +7114,7 @@ static void fill_var_sinfo(const struct dump_ctx *ctx, struct vrend_variable_sha
    sinfo->num_in_cull = has_prop ? ctx->num_cull_dist_prop : ctx->key->num_in_cull;
    sinfo->num_out_clip = has_prop ? ctx->num_clip_dist_prop : ctx->key->num_out_clip;
    sinfo->num_out_cull = has_prop ? ctx->num_cull_dist_prop : ctx->key->num_out_cull;
+   sinfo->legacy_color_bits = ctx->color_out_mask;
 }
 
 static void fill_sinfo(const struct dump_ctx *ctx, struct vrend_shader_info *sinfo)

src/vrend_shader.h

@@ -136,6 +136,7 @@ struct vrend_variable_shader_info {
    uint32_t num_out_clip:4;
    uint32_t num_out_cull:4;
    int num_ucp;
+   int legacy_color_bits;
 };
 
 struct vrend_shader_key {
@@ -159,6 +160,7 @@ struct vrend_shader_key {
          uint32_t logicop_enabled : 1;
          uint32_t prim_is_points : 1;
          uint32_t invert_origin : 1;
+         uint32_t available_color_in_bits : 4;
       } fs;
 
       struct {