graphics: preserve logical alpha when blending reordered targets (PPSA02721)

Co-authored-by: EmK530 <admin@emk530.net>

src/graphics/host_gpu/renderer/pipeline/blendMapping.cpp

@@ -0,0 +1,58 @@
+#include "graphics/host_gpu/renderer/pipeline/blendMapping.h"
+
+#include "graphics/guest_gpu/hardwareContext.h"
+
+#include <initializer_list>
+
+namespace Libs::Graphics {
+
+bool BlendFactorIsDualSource(uint8_t factor) {
+	return factor >= static_cast<uint8_t>(Prospero::BlendFactor::kSrc1Color) &&
+	       factor <= static_cast<uint8_t>(Prospero::BlendFactor::kOneMinusSrc1Alpha);
+}
+
+namespace {
+
+bool BlendFactorIsConstantColor(uint8_t factor) {
+	return factor == static_cast<uint8_t>(Prospero::BlendFactor::kConstantColor) ||
+	       factor == static_cast<uint8_t>(Prospero::BlendFactor::kOneMinusConstantColor);
+}
+
+} // namespace
+
+BlendMappingSupport ClassifyBlendMapping(const HW::BlendControl&                blend,
+                                         const Prospero::ColorComponentMapping& mapping) {
+	// Color constants are not swizzled with the exports; scalar constant alpha is unaffected.
+	if (!mapping.IsIdentity() && (BlendFactorIsConstantColor(blend.color_srcblend) ||
+	                              BlendFactorIsConstantColor(blend.color_destblend))) {
+		return BlendMappingSupport::Unsupported;
+	}
+	if (mapping.Map(3) == 3u) {
+		return BlendMappingSupport::Direct;
+	}
+	// Moving alpha requires the same equation for all channels.
+	if (blend.separate_alpha_blend && (blend.alpha_srcblend != blend.color_srcblend ||
+	                                   blend.alpha_destblend != blend.color_destblend ||
+	                                   blend.alpha_comb_fcn != blend.color_comb_fcn)) {
+		return BlendMappingSupport::Unsupported;
+	}
+	auto support = BlendMappingSupport::Direct;
+	for (const auto factor: {blend.color_srcblend, blend.color_destblend}) {
+		if (BlendFactorIsDualSource(factor)) {
+			return BlendMappingSupport::Unsupported;
+		}
+		switch (static_cast<Prospero::BlendFactor>(factor)) {
+			case Prospero::BlendFactor::kSrcAlpha:
+			case Prospero::BlendFactor::kOneMinusSrcAlpha:
+				support = BlendMappingSupport::SourceAlpha;
+				break;
+			case Prospero::BlendFactor::kDstAlpha:
+			case Prospero::BlendFactor::kOneMinusDstAlpha:
+			case Prospero::BlendFactor::kSrcAlphaSaturate: return BlendMappingSupport::Unsupported;
+			default: break;
+		}
+	}
+	return support;
+}
+
+} // namespace Libs::Graphics

src/graphics/host_gpu/renderer/pipeline/blendMapping.h

@@ -0,0 +1,27 @@
+#ifndef EMULATOR_SRC_GRAPHICS_HOST_GPU_RENDERER_PIPELINE_BLENDMAPPING_H_
+#define EMULATOR_SRC_GRAPHICS_HOST_GPU_RENDERER_PIPELINE_BLENDMAPPING_H_
+
+#include <cstdint>
+
+namespace Libs::Graphics {
+
+namespace HW {
+struct BlendControl;
+}
+namespace Prospero {
+struct ColorComponentMapping;
+}
+
+enum class BlendMappingSupport {
+	Direct,
+	SourceAlpha, // Requires logical alpha in the second blend source.
+	Unsupported,
+};
+
+bool                BlendFactorIsDualSource(uint8_t factor);
+BlendMappingSupport ClassifyBlendMapping(const HW::BlendControl&                blend,
+                                         const Prospero::ColorComponentMapping& mapping);
+
+} // namespace Libs::Graphics
+
+#endif // EMULATOR_SRC_GRAPHICS_HOST_GPU_RENDERER_PIPELINE_BLENDMAPPING_H_

src/graphics/host_gpu/renderer/pipeline/pipelineCache.cpp

@@ -11,6 +11,7 @@
 #include "graphics/host_gpu/renderer/debug.h"
 #include "graphics/host_gpu/renderer/depthRenderTarget.h"
 #include "graphics/host_gpu/renderer/image/imageView.h"
+#include "graphics/host_gpu/renderer/pipeline/blendMapping.h"
 #include "graphics/host_gpu/renderer/render.h"
 #include "graphics/host_gpu/renderer/renderContext.h"
 #include "graphics/shader/recompiler/ShaderRecompiler.h"
@@ -609,21 +610,30 @@ PipelineCache::GraphicsPrograms PipelineCache::GetGraphicsPrograms(
 	}
 	ShaderParams pixel_params;
 	if (pixel_active) {
-		pixel_params = PrepareProgram(pixel_regs, sh, target_export_mapping, pixel_info);
-		const auto& blend          = context.GetBlendControl(0);
-		const auto  is_dual_source = [](uint8_t factor) {
-			return factor >= static_cast<uint8_t>(Prospero::BlendFactor::kSrc1Color) &&
-			       factor <= static_cast<uint8_t>(Prospero::BlendFactor::kOneMinusSrc1Alpha);
-		};
+		pixel_params      = PrepareProgram(pixel_regs, sh, target_export_mapping, pixel_info);
+		const auto& blend = context.GetBlendControl(0);
 		pixel_info.dual_source_blending =
 		    blend.enable && !context.GetRenderTarget(0).info.blend_bypass &&
-		    (is_dual_source(blend.color_srcblend) || is_dual_source(blend.color_destblend) ||
-		     (blend.separate_alpha_blend &&
-		      (is_dual_source(blend.alpha_srcblend) || is_dual_source(blend.alpha_destblend))));
+		    (BlendFactorIsDualSource(blend.color_srcblend) ||
+		     BlendFactorIsDualSource(blend.color_destblend) ||
+		     (blend.separate_alpha_blend && (BlendFactorIsDualSource(blend.alpha_srcblend) ||
+		                                     BlendFactorIsDualSource(blend.alpha_destblend))));
 		if (pixel_info.dual_source_blending) {
-			// MRT1 supplies a second blend source for the same render target as MRT0.
+			// MRT1 supplies the second blend source for target 0.
 			pixel_info.target_output_mode[1]    = pixel_info.target_output_mode[0];
 			pixel_info.target_export_mapping[1] = pixel_info.target_export_mapping[0];
+		} else if (blend.enable && !context.GetRenderTarget(0).info.blend_bypass &&
+		           pixel_info.target_output_mode[0] != 0 && pixel_info.target_output_mode[0] != 7 &&
+		           std::all_of(std::begin(pixel_info.target_output_mode) + 1,
+		                       std::end(pixel_info.target_output_mode),
+		                       [](uint8_t mode) { return mode == 0; }) &&
+		           ClassifyBlendMapping(blend, pixel_info.target_export_mapping[0]) ==
+		               BlendMappingSupport::SourceAlpha) {
+			// Preserve logical alpha when the export mapping moves it.
+			pixel_info.alpha_blend_source_remap = true;
+			pixel_info.dual_source_blending     = true;
+			pixel_info.target_output_mode[1]    = pixel_info.target_output_mode[0];
+			pixel_info.target_export_mapping[1] = {};
 		}
 	}
 	if (context.GetClipControl().clip_disable) {
@@ -720,7 +730,24 @@ PipelineCache::Pipeline& PipelineCache::GetGraphicsPipeline(
 		static_params.alpha_comb_fcn[slot]       = bc.alpha_comb_fcn;
 		static_params.alpha_destblend[slot]      = bc.alpha_destblend;
 		static_params.separate_alpha_blend[slot] = bc.separate_alpha_blend;
-		static_params.blend_enable[slot]         = bc.enable && !rt.info.blend_bypass;
+		const bool alpha_remap =
+		    slot == 0 && ps_input_info != nullptr && ps_input_info->alpha_blend_source_remap;
+		static_params.blend_enable[slot] = bc.enable && !rt.info.blend_bypass;
+		if (static_params.blend_enable[slot] && !alpha_remap &&
+		    ClassifyBlendMapping(bc, colors[i].export_mapping) != BlendMappingSupport::Direct) {
+			static_params.blend_enable[slot] = false;
+			static std::atomic_bool warned = false;
+			if (!warned.exchange(true, std::memory_order_relaxed)) {
+				Log::WriteToConsoleAndLog(fmt::format(
+				    "Warning: blending disabled for unsupported color mapping "
+				    "(slot={} mapping=0x{:02x} color={}/{} alpha={}/{} separate={}).\n",
+				    slot, colors[i].export_mapping.packed, bc.color_srcblend, bc.color_destblend,
+				    bc.alpha_srcblend, bc.alpha_destblend, bc.separate_alpha_blend ? 1 : 0));
+			}
+		}
+		if (alpha_remap) {
+			static_params.blend_alpha_source_remap = true;
+		}
 	}
 	const bool with_depth =
 	    depth.desc.view_info.format != vk::Format::eUndefined && static_cast<bool>(depth.image_id);

src/graphics/host_gpu/renderer/pipeline/pipelineCache.h

@@ -55,6 +55,7 @@ struct PipelineStaticParameters {
 	uint8_t                    alpha_destblend[RENDER_COLOR_ATTACHMENTS_MAX]      = {};
 	bool                       separate_alpha_blend[RENDER_COLOR_ATTACHMENTS_MAX] = {};
 	bool                       blend_enable[RENDER_COLOR_ATTACHMENTS_MAX]         = {};
+	bool                       blend_alpha_source_remap                           = false;
 
 	bool operator==(const PipelineStaticParameters& other) const noexcept;
 };
@@ -64,7 +65,7 @@ struct PipelineStaticParameters {
 static_assert(std::is_trivially_copyable_v<PipelineStaticParameters>);
 static_assert(std::is_standard_layout_v<PipelineStaticParameters>);
 static_assert(alignof(PipelineStaticParameters) == 1);
-static_assert(sizeof(PipelineStaticParameters) == 125);
+static_assert(sizeof(PipelineStaticParameters) == 126);
 
 struct PipelineRenderingState {
 	std::array<vk::Format, RENDER_COLOR_ATTACHMENTS_MAX> color_formats {};

src/graphics/host_gpu/renderer/pipeline/shaders.cpp

@@ -137,14 +137,17 @@ static void GetInputFormat(const ShaderBufferResource& res, vk::Format& format,
 	}
 }
 
-static vk::BlendFactor GetBlendFactor(uint32_t factor) {
+static vk::BlendFactor GetBlendFactor(uint32_t factor, bool remap_source_alpha) {
 	switch (static_cast<Prospero::BlendFactor>(factor)) {
 		case Prospero::BlendFactor::kZero: return vk::BlendFactor::eZero;
 		case Prospero::BlendFactor::kOne: return vk::BlendFactor::eOne;
 		case Prospero::BlendFactor::kSrcColor: return vk::BlendFactor::eSrcColor;
 		case Prospero::BlendFactor::kOneMinusSrcColor: return vk::BlendFactor::eOneMinusSrcColor;
-		case Prospero::BlendFactor::kSrcAlpha: return vk::BlendFactor::eSrcAlpha;
-		case Prospero::BlendFactor::kOneMinusSrcAlpha: return vk::BlendFactor::eOneMinusSrcAlpha;
+		case Prospero::BlendFactor::kSrcAlpha:
+			return remap_source_alpha ? vk::BlendFactor::eSrc1Color : vk::BlendFactor::eSrcAlpha;
+		case Prospero::BlendFactor::kOneMinusSrcAlpha:
+			return remap_source_alpha ? vk::BlendFactor::eOneMinusSrc1Color
+			                          : vk::BlendFactor::eOneMinusSrcAlpha;
 		case Prospero::BlendFactor::kDstAlpha: return vk::BlendFactor::eDstAlpha;
 		case Prospero::BlendFactor::kOneMinusDstAlpha: return vk::BlendFactor::eOneMinusDstAlpha;
 		case Prospero::BlendFactor::kDstColor: return vk::BlendFactor::eDstColor;
@@ -397,17 +400,20 @@ void CreatePipelineInternal(GraphicContext& graphics, PipelineCache::Pipeline& p
 		color_blend_attachment[i].colorWriteMask =
 		    vk::ColorComponentFlags {static_params.color_mask[i]};
 		color_blend_attachment[i].blendEnable = static_params.blend_enable[i] ? VK_TRUE : VK_FALSE;
+		// Only target 0 can use the second blend source carrying logical alpha.
+		const bool remap_source_alpha         = i == 0 && static_params.blend_alpha_source_remap;
 		color_blend_attachment[i].srcColorBlendFactor =
-		    GetBlendFactor(static_params.color_srcblend[i]);
+		    GetBlendFactor(static_params.color_srcblend[i], remap_source_alpha);
 		color_blend_attachment[i].dstColorBlendFactor =
-		    GetBlendFactor(static_params.color_destblend[i]);
+		    GetBlendFactor(static_params.color_destblend[i], remap_source_alpha);
 		color_blend_attachment[i].colorBlendOp = GetBlendOp(static_params.color_comb_fcn[i]);
 		color_blend_attachment[i].srcAlphaBlendFactor =
-		    (static_params.separate_alpha_blend[i] ? GetBlendFactor(static_params.alpha_srcblend[i])
-		                                           : color_blend_attachment[i].srcColorBlendFactor);
+		    (static_params.separate_alpha_blend[i]
+		         ? GetBlendFactor(static_params.alpha_srcblend[i], remap_source_alpha)
+		         : color_blend_attachment[i].srcColorBlendFactor);
 		color_blend_attachment[i].dstAlphaBlendFactor =
 		    (static_params.separate_alpha_blend[i]
-		         ? GetBlendFactor(static_params.alpha_destblend[i])
+		         ? GetBlendFactor(static_params.alpha_destblend[i], remap_source_alpha)
 		         : color_blend_attachment[i].dstColorBlendFactor);
 		color_blend_attachment[i].alphaBlendOp =
 		    (static_params.separate_alpha_blend[i] ? GetBlendOp(static_params.alpha_comb_fcn[i])

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

@@ -452,6 +452,11 @@ void EmitSetAttribute(ValueEmitContext& ctx, const IR::Inst& inst) {
 	if (exp.kind == IR::ExportTargetKind::Null || exp.en == 0u) {
 		return;
 	}
+	// Skip dormant color exports after their valid mask; MRT1 is reserved for logical alpha.
+	if (state.program.stage == ShaderType::Pixel && exp.kind == IR::ExportTargetKind::Mrt &&
+	    exp.index != 0 && state.input_info.pixel->alpha_blend_source_remap) {
+		return;
+	}
 	EmitIfCondition(state, exec, [&]() {
 		const auto data = ctx.Arg(inst, 0);
 		if (exp.kind == IR::ExportTargetKind::Primitive) {
@@ -492,6 +497,18 @@ void EmitSetAttribute(ValueEmitContext& ctx, const IR::Inst& inst) {
 		const bool uint_output = MrtOutputMode(state, exp) == 7u;
 		const auto vector_type = uint_output ? TypeU32Vector(state, 4) : TypeF32Vector(state, 4);
 		auto       value       = ExportVector(ctx, data, exp, uint_output);
+		if (state.program.stage == ShaderType::Pixel && exp.kind == IR::ExportTargetKind::Mrt &&
+		    exp.index == 0 && !uint_output && state.input_info.pixel->alpha_blend_source_remap) {
+			// Broadcast logical alpha before swizzling the primary output.
+			const auto blend_output =
+			    OutputVariableForExport(state, {.kind = IR::ExportTargetKind::Mrt, .index = 1});
+			if (blend_output != 0) {
+				const auto alpha = state.builder.AllocateId();
+				state.builder.AddFunction(spv::OpVectorShuffle, vector_type, alpha, value, value,
+				                          3u, 3u, 3u, 3u);
+				state.builder.AddFunction(spv::OpStore, blend_output, alpha);
+			}
+		}
 		if (state.program.stage == ShaderType::Pixel && exp.kind == IR::ExportTargetKind::Mrt &&
 		    exp.index < state.input_info.pixel->target_export_mapping.size()) {
 			const auto mapping = state.input_info.pixel->target_export_mapping[exp.index];

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

@@ -326,6 +326,8 @@ void CollectBuiltinInputs(const Program& program, ShaderInfo& info) {
 }
 
 void CollectOutputs(const Program& program, ShaderStageInputInfo input_info, ShaderInfo& info) {
+	const bool alpha_remap = program.stage == ShaderType::Pixel && input_info.pixel != nullptr &&
+	                         input_info.pixel->alpha_blend_source_remap;
 	for (const auto* block: program.blocks) {
 		for (const auto& inst: *block) {
 			if (inst.GetOpcode() != ValueOpcode::SetAttribute) {
@@ -385,8 +387,14 @@ void CollectOutputs(const Program& program, ShaderStageInputInfo input_info, Sha
 					          export_info.index, fmt::format("out_param_{}", export_info.index));
 					break;
 				case ExportTargetKind::Mrt:
+					if (alpha_remap && export_info.index != 0) {
+						break;
+					}
 					AddOutput(info, StageOutputKind::Mrt, export_info.index, export_info.index,
 					          fmt::format("out_mrt_{}", export_info.index));
+					if (alpha_remap) {
+						AddOutput(info, StageOutputKind::Mrt, 1, 1, "out_mrt_1");
+					}
 					break;
 				default: break;
 			}

src/graphics/shader/shader.cpp

@@ -693,6 +693,7 @@ void BuildStageStaticKey(const ShaderPixelInputInfo& info, std::vector<uint32_t>
 	key.push_back(static_cast<uint32_t>(info.ps_sample_mask_export_enable));
 	key.push_back(static_cast<uint32_t>(info.ps_early_z));
 	key.push_back(static_cast<uint32_t>(info.dual_source_blending));
+	key.push_back(static_cast<uint32_t>(info.alpha_blend_source_remap));
 	key.insert(key.end(), std::begin(info.target_output_mode), std::end(info.target_output_mode));
 	for (uint32_t base = 0; base < info.target_export_mapping.size(); base += 4u) {
 		uint32_t packed = 0;

src/graphics/shader/shader.h

@@ -178,6 +178,8 @@ struct ShaderPixelInputInfo {
 	bool                                           ps_sample_mask_export_enable = false;
 	bool                                           ps_sample_shading            = false;
 	bool                                           dual_source_blending         = false;
+	// Export logical alpha through MRT1 for blending after channel swizzling.
+	bool                                           alpha_blend_source_remap     = false;
 	bool                                           ps_early_z                   = false;
 	bool                                           ps_execute_on_noop           = false;
 	ShaderStageRuntime                             stage;