r5xx: Enable depth write emission.

Thanks to nh for the r3xx version.

src/mesa/drivers/dri/r300/r300_context.h

@@ -833,6 +833,8 @@ struct r500_fragment_program {
 
 	int max_temp_idx;
 
+	GLboolean writes_depth;
+
 	GLuint optimization;
 };
 

src/mesa/drivers/dri/r300/r300_state.c

@@ -411,7 +411,10 @@ static GLboolean current_fragment_program_writes_depth(GLcontext* ctx)
 			(char *)ctx->FragmentProgram._Current;
 		return (fp && fp->WritesDepth);
 	} else {
-		return GL_FALSE; /* TODO: Verify depth writing works on R5xx */
+		struct r500_fragment_program* fp =
+			(struct r500_fragment_program*)(char*)
+			ctx->FragmentProgram._Current;
+		return (fp && fp->writes_depth);
 	}
 }
 

src/mesa/drivers/dri/r300/r500_fragprog.c

@@ -365,7 +365,9 @@ static void emit_alu(struct r500_fragment_program *fp, int counter, struct prog_
 			fp->inst[counter].inst0 |= (fpi->DstReg.WriteMask << 15);
 
 		if (fpi->DstReg.Index == FRAG_RESULT_DEPR)
-			fp->inst[counter].inst4 = R500_ALPHA_W_OMASK;
+			fp->inst[counter].inst4 |= R500_ALPHA_W_OMASK;
+			/* Notify the state emission! */
+			fp->writes_depth = GL_TRUE;
 	} else {
 		fp->inst[counter].inst0 = R500_INST_TYPE_ALU
 			/* pixel_mask */
@@ -1251,6 +1253,8 @@ static void init_program(r300ContextPtr r300, struct r500_fragment_program *fp)
 	fp->max_temp_idx = 1;
 	/* Temp register offset. */
 	fp->temp_reg_offset = 0;
+	/* Whether or not we perform any depth writing. */
+	fp->writes_depth = GL_FALSE;
 
 	_mesa_memset(cs, 0, sizeof(*fp->cs));
 	for (i = 0; i < PFS_MAX_ALU_INST; i++) {