glsl: Add support for specifying the component in textureGather

ARB_gpu_shader5 introduces new variants of textureGather* which have an
explicit component selector, rather than relying purely on the sampler's
swizzle state.

This patch adds the GLSL plumbing for the extra parameter.

Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/glsl/ir_reader.cpp

@@ -934,6 +934,7 @@ ir_reader::read_texture(s_expression *expr)
    s_list *s_shadow = NULL;
    s_expression *s_lod = NULL;
    s_expression *s_sample_index = NULL;
+   s_expression *s_component = NULL;
 
    ir_texture_opcode op = ir_tex; /* silence warning */
 
@@ -948,7 +949,7 @@ ir_reader::read_texture(s_expression *expr)
    s_pattern txs_pattern[] =
       { "txs", s_type, s_sampler, s_lod };
    s_pattern tg4_pattern[] =
-      { "tg4", s_type, s_sampler, s_coord, s_offset };
+      { "tg4", s_type, s_sampler, s_coord, s_offset, s_component };
    s_pattern query_levels_pattern[] =
       { "query_levels", s_type, s_sampler };
    s_pattern other_pattern[] =
@@ -1089,6 +1090,13 @@ ir_reader::read_texture(s_expression *expr)
       }
       break;
    }
+   case ir_tg4:
+      tex->lod_info.component = read_rvalue(s_component);
+      if (tex->lod_info.component == NULL) {
+         ir_read_error(NULL, "when reading component in (tg4 ...)");
+         return NULL;
+      }
+      break;
    default:
       // tex and lod don't have any extra parameters.
       break;