Fix pixel shader input aliases

src/graphics/shader/recompiler/backend/spirv/spirvEmitterModule.cpp

@@ -388,6 +388,19 @@ void DefineInputs(EmitterState& state) {
 		}
 	}
 	for (auto& input: state.inputs) {
+		if (state.program.stage == ShaderType::Pixel &&
+		    input.kind == IR::StageInputKind::Parameter) {
+			const auto location = PixelParameterLocation(state, input.location);
+			const auto alias = std::ranges::find_if(state.inputs, [&](const InputBinding& other) {
+				return other.kind == IR::StageInputKind::Parameter && other.variable_id != 0 &&
+				       PixelParameterLocation(state, other.location) == location;
+			});
+			if (alias != state.inputs.end()) {
+				EXIT_IF(alias->per_vertex != input.per_vertex);
+				input.variable_id = alias->variable_id;
+				continue;
+			}
+		}
 		uint32_t type = TypeU32(state);
 		switch (input.kind) {
 			case IR::StageInputKind::VertexIndex:

src/graphics/shader/recompiler/ir/passes/ShaderInfoCollection.cpp

@@ -226,6 +226,18 @@ void CollectPixelInputs(const Program& program, const ShaderPixelInputInfo* pixe
 			}
 		}
 	}
+	// Aliases of a vertex output share one SPIR-V interface variable. If any
+	// alias reads raw vertices, interpolate the other aliases from those too.
+	for (uint32_t input = 0; input < pixel->input_num; input++) {
+		for (uint32_t alias = 0; alias < pixel->input_num; alias++) {
+			if (ShaderPixelParameterMappedLocation(*pixel, input) ==
+			        ShaderPixelParameterMappedLocation(*pixel, alias) &&
+			    ShaderPixelParameterIsFlat(*pixel, input) ==
+			        ShaderPixelParameterIsFlat(*pixel, alias)) {
+				per_vertex[input] = per_vertex[input] || per_vertex[alias];
+			}
+		}
+	}
 	for (uint32_t input = 0; input < pixel->input_num; input++) {
 		AddInput(info, StageInputKind::Parameter, input, 4, fmt::format("in_param_{}", input),
 		         per_vertex[input]);

src/graphics/shader/rectListShader.cpp

@@ -40,12 +40,15 @@ std::vector<Parameter> GetParameters(const ShaderVertexInputInfo& vertex_info,
 	}
 
 	std::vector<Parameter> parameters;
+	std::array<bool, 32> output_locations {};
 	for (const auto input: active_inputs) {
 		const auto input_location = ShaderPixelParameterMappedLocation(*pixel_info, input);
-		if ((vertex_info.stage.program->param_export_mask & (1u << input_location)) != 0) {
-			parameters.push_back({input_location,
-			                      ShaderPixelParameterLocation(*pixel_info, active_inputs, input),
+		const auto output_location = ShaderPixelParameterLocation(*pixel_info, active_inputs, input);
+		if ((vertex_info.stage.program->param_export_mask & (1u << input_location)) != 0 &&
+		    !output_locations[output_location]) {
+			parameters.push_back({input_location, output_location,
 			                      ShaderPixelParameterIsFlat(*pixel_info, input)});
+			output_locations[output_location] = true;
 		}
 	}
 	return parameters;

src/graphics/shader/shaderPixelParameter.cpp

@@ -19,19 +19,31 @@ uint32_t ShaderPixelParameterLocation(const ShaderPixelInputInfo& info,
                                       std::span<const uint32_t> active_inputs, uint32_t input) {
 	std::array<bool, 32> used_locations {};
 	for (const auto active_input: active_inputs) {
-		auto location = ShaderPixelParameterMappedLocation(info, active_input);
-		if (location < used_locations.size() && used_locations[location]) {
-			location = active_input;
-			while (location < used_locations.size() && used_locations[location]) {
-				location++;
+		used_locations[ShaderPixelParameterMappedLocation(info, active_input)] = true;
+	}
+	std::array<uint32_t, 64> group_locations;
+	group_locations.fill(UINT32_MAX);
+	for (const auto active_input: active_inputs) {
+		const auto mapped = ShaderPixelParameterMappedLocation(info, active_input);
+		const auto group  = mapped * 2u + ShaderPixelParameterIsFlat(info, active_input);
+		auto&      location = group_locations[group];
+		if (location == UINT32_MAX) {
+			location = mapped;
+			// Smooth and custom interpolation read the same vertex output. Only
+			// differing flat/smooth rectangle outputs need separate locations.
+			if (group_locations[group ^ 1u] != UINT32_MAX) {
+				location = 0;
+				while (location < used_locations.size() && used_locations[location]) {
+					location++;
+				}
+				EXIT_NOT_IMPLEMENTED(location >= used_locations.size());
 			}
-			EXIT_NOT_IMPLEMENTED(location >= used_locations.size());
+			used_locations[location] = true;
 		}
 
 		if (active_input == input) {
 			return location;
 		}
-		used_locations[location] = true;
 	}
 	return ShaderPixelParameterMappedLocation(info, input);
 }