radeonsi: interpolate varyings at sample when full sample shading is enabled

src/gallium/drivers/radeonsi/si_shader.c

@@ -421,27 +421,27 @@ static void declare_input_fs(
 					   shader->input[input_index].param_offset);
 
 	switch (decl->Interp.Interpolate) {
-	case TGSI_INTERPOLATE_COLOR:
-		if (si_shader_ctx->shader->key.ps.flatshade) {
-			interp_param = 0;
-		} else {
-			if (decl->Interp.Centroid)
-				interp_param = LLVMGetParam(main_fn, SI_PARAM_PERSP_CENTROID);
-			else
-				interp_param = LLVMGetParam(main_fn, SI_PARAM_PERSP_CENTER);
-		}
-		break;
 	case TGSI_INTERPOLATE_CONSTANT:
 		interp_param = 0;
 		break;
 	case TGSI_INTERPOLATE_LINEAR:
-		if (decl->Interp.Centroid)
+		if (si_shader_ctx->shader->key.ps.interp_at_sample)
+			interp_param = LLVMGetParam(main_fn, SI_PARAM_LINEAR_SAMPLE);
+		else if (decl->Interp.Centroid)
 			interp_param = LLVMGetParam(main_fn, SI_PARAM_LINEAR_CENTROID);
 		else
 			interp_param = LLVMGetParam(main_fn, SI_PARAM_LINEAR_CENTER);
 		break;
+	case TGSI_INTERPOLATE_COLOR:
+		if (si_shader_ctx->shader->key.ps.flatshade) {
+			interp_param = 0;
+			break;
+		}
+		/* fall through to perspective */
 	case TGSI_INTERPOLATE_PERSPECTIVE:
-		if (decl->Interp.Centroid)
+		if (si_shader_ctx->shader->key.ps.interp_at_sample)
+			interp_param = LLVMGetParam(main_fn, SI_PARAM_PERSP_SAMPLE);
+		else if (decl->Interp.Centroid)
 			interp_param = LLVMGetParam(main_fn, SI_PARAM_PERSP_CENTROID);
 		else
 			interp_param = LLVMGetParam(main_fn, SI_PARAM_PERSP_CENTER);

src/gallium/drivers/radeonsi/si_shader.h

@@ -158,6 +158,7 @@ union si_shader_key {
 		unsigned	color_two_side:1;
 		unsigned	alpha_func:3;
 		unsigned	flatshade:1;
+		unsigned	interp_at_sample:1;
 		unsigned	alpha_to_one:1;
 	} ps;
 	struct {

src/gallium/drivers/radeonsi/si_state.c

@@ -2115,6 +2115,8 @@ static INLINE void si_shader_selector_key(struct pipe_context *ctx,
 		if (sctx->queued.named.rasterizer) {
 			key->ps.color_two_side = sctx->queued.named.rasterizer->two_side;
 			key->ps.flatshade = sctx->queued.named.rasterizer->flatshade;
+			key->ps.interp_at_sample = sctx->framebuffer.nr_samples > 1 &&
+						   sctx->ps_iter_samples == sctx->framebuffer.nr_samples;
 
 			if (sctx->queued.named.blend) {
 				key->ps.alpha_to_one = sctx->queued.named.blend->alpha_to_one &&