mesa: Add support for the ARB_fragment_program part of ARB_draw_buffers.

Fixes fbo-drawbuffers-arbfp.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=34321
Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>

src/mesa/program/program_parse.y

@@ -2064,6 +2064,34 @@ optResultFaceType:
 	      ? VERT_RESULT_COL0
 	      : FRAG_RESULT_COLOR;
 	}
+	| '[' INTEGER ']'
+	{
+	   if (state->mode == ARB_vertex) {
+	      yyerror(& @1, state, "invalid program result name");
+	      YYERROR;
+	   } else {
+	      if (!state->option.DrawBuffers) {
+		 /* From the ARB_draw_buffers spec (same text exists
+		  * for ATI_draw_buffers):
+		  *
+		  *     If this option is not specified, a fragment
+		  *     program that attempts to bind
+		  *     "result.color[n]" will fail to load, and only
+		  *     "result.color" will be allowed.
+		  */
+		 yyerror(& @1, state,
+			 "result.color[] used without "
+			 "`OPTION ARB_draw_buffers' or "
+			 "`OPTION ATI_draw_buffers'");
+		 YYERROR;
+	      } else if ($2 >= state->MaxDrawBuffers) {
+		 yyerror(& @1, state,
+			 "result.color[] exceeds MAX_DRAW_BUFFERS_ARB");
+		 YYERROR;
+	      }
+	      $$ = FRAG_RESULT_DATA0 + $2;
+	   }
+	}
 	| FRONT
 	{
 	   if (state->mode == ARB_vertex) {
@@ -2681,6 +2709,7 @@ _mesa_parse_arb_program(struct gl_context *ctx, GLenum target, const GLubyte *st
    state->MaxClipPlanes = ctx->Const.MaxClipPlanes;
    state->MaxLights = ctx->Const.MaxLights;
    state->MaxProgramMatrices = ctx->Const.MaxProgramMatrices;
+   state->MaxDrawBuffers = ctx->Const.MaxDrawBuffers;
 
    state->state_param_enum = (target == GL_VERTEX_PROGRAM_ARB)
       ? STATE_VERTEX_PROGRAM : STATE_FRAGMENT_PROGRAM;

src/mesa/program/program_parser.h

@@ -173,6 +173,7 @@ struct asm_parser_state {
    unsigned MaxClipPlanes;
    unsigned MaxLights;
    unsigned MaxProgramMatrices;
+   unsigned MaxDrawBuffers;
    /*@}*/
 
    /**