shader: fix mismatching shader invariants on GL

On OpenGL with GLSL < 4.30 the invariant input specifiers must match the
invariant output specifiers of the previous stage.

Fixes #75

Signed-off-by: Gert Wollny <gert.wollny@collabora.com>
Reviewed-by: Gurchetan Singh <gurchetansingh@chromium.org>

src/vrend_renderer.c

@@ -3139,6 +3139,7 @@ static inline void vrend_fill_shader_key(struct vrend_context *ctx,
       memcpy(key->prev_stage_generic_and_patch_outputs_layout,
              ctx->sub->shaders[prev_type]->sinfo.generic_outputs_layout,
              64 * sizeof (struct vrend_layout_info));
+      key->force_invariant_inputs = ctx->sub->shaders[prev_type]->sinfo.invariant_outputs;
    }
 
    int next_type = -1;

src/vrend_shader.c

@@ -4644,6 +4644,15 @@ iter_instruction(struct tgsi_iterate_context *iter,
       }
       if (ctx->so)
          prepare_so_movs(ctx);
+
+      /* GLES doesn't allow invariant specifiers on inputs, but on GL with
+       * GLSL < 4.30 it is required to match the output of the previous stage */
+      if (!ctx->cfg->use_gles) {
+         for (unsigned i = 0; i < ctx->num_inputs; ++i) {
+            if (ctx->key->force_invariant_inputs & (1ull << i))
+               ctx->inputs[i].invariant = 1;
+         }
+      }
    }
 
    if (!get_destination_info(ctx, inst, &dinfo, dsts, fp64_dsts, writemask))
@@ -6567,6 +6576,11 @@ static void fill_sinfo(struct dump_ctx *ctx, struct vrend_shader_info *sinfo)
    sinfo->image_arrays = ctx->image_arrays;
    sinfo->num_image_arrays = ctx->num_image_arrays;
    sinfo->generic_inputs_emitted_mask = ctx->generic_inputs_emitted_mask;
+
+   for (unsigned i = 0; i < ctx->num_outputs; ++i) {
+      if (ctx->outputs[i].invariant)
+         sinfo->invariant_outputs |= 1ull << i;
+   }
 }
 
 static bool allocate_strbuffers(struct dump_ctx* ctx)

src/vrend_shader.h

@@ -90,6 +90,7 @@ struct vrend_shader_info {
 
    struct vrend_interp_info *interpinfo;
    char **so_names;
+   uint64_t invariant_outputs;
 };
 
 struct vrend_shader_key {
@@ -125,6 +126,7 @@ struct vrend_shader_key {
    uint8_t num_indirect_patch_inputs;
    uint32_t generic_outputs_expected_mask;
    uint8_t fs_swizzle_output_rgb_to_bgr;
+   uint64_t force_invariant_inputs;
 };
 
 struct vrend_shader_cfg {