Honor explicit gather LOD with shared image mip selection

Co-authored-by: YuhiAida <21134775+YuhiAida@users.noreply.github.com>
Co-authored-by: BlackCAT <52720489+psnwd@users.noreply.github.com>
Co-authored-by: shadowbeat070 <70843316+shadowbeat070@users.noreply.github.com>
Co-authored-by: Senaxx <michelbeld@gmail.com>
Co-authored-by: Mac <me@itsmemac.com>
Co-authored-by: Ali Almohaya <AliAlmohaya@gmail.com>

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

@@ -41,7 +41,7 @@ void ValidateNativeProgram(const IR::Program& program) {
 			Fail(program, "native shader plan has an invalid image class");
 		}
 		present[static_cast<size_t>(*kind)] = true;
-		const auto dynamic = program.info.images[i].mip_mode == IR::ImageMipMode::DynamicStorage;
+		const auto dynamic = program.info.images[i].mip_mode == IR::ImageMipMode::Dynamic;
 		const auto count   = dynamic ? program.info.images[i].mip_count : 1u;
 		if (count == 0u || (!dynamic && program.info.images[i].mip_count != 1u)) {
 			Fail(program, "native shader plan has an invalid image mip descriptor count");

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

@@ -152,20 +152,11 @@ uint32_t ImageViewSizeType(EmitterState& state, ImageDimension dimension) {
 	}
 }
 
-uint32_t LoadSampledImageDescriptor(EmitterState& state, uint32_t resource) {
-	const auto& image_resource = state.program.info.images.at(resource);
-	EXIT_IF(image_resource.resource_class != IR::ImageResourceClass::Sampled);
-	const auto kind = IR::DescriptorBindingForImage(image_resource);
-	EXIT_IF(!kind.has_value());
-	const auto array_index  = ResourceForDescriptor(state, *kind, resource);
-	const auto variable     = state.image_variables[IR::ImageBindingIndex(*kind)];
-	const auto pointer_type = state.builder.Type(
-	    spv::OpTypePointer, spv::StorageClassUniformConstant, ImageType(state, image_resource));
-	const auto pointer =
-	    DescriptorElementPointer(state, pointer_type, variable, array_index, *kind, resource,
-	                             "sampled image descriptor array was not emitted");
+uint32_t LoadImageDescriptor(EmitterState& state, uint32_t resource, uint32_t mip) {
+	const auto pointer = ImageDescriptorPointer(state, resource, mip);
 	const auto image = state.builder.AllocateId();
-	state.builder.AddFunction(spv::OpLoad, ImageType(state, image_resource), image, pointer);
+	state.builder.AddFunction(spv::OpLoad, ImageType(state, state.program.info.images.at(resource)),
+	                          image, pointer);
 	return image;
 }
 
@@ -183,10 +174,10 @@ uint32_t LoadSamplerDescriptor(EmitterState& state, uint32_t sampler) {
 	return sampler_id;
 }
 
-uint32_t MakeSampledImage(EmitterState& state, uint32_t resource, uint32_t sampler) {
+uint32_t MakeSampledImage(EmitterState& state, uint32_t resource, uint32_t sampler_id, uint32_t mip) {
 	const auto& image_resource = state.program.info.images.at(resource);
-	const auto  image          = LoadSampledImageDescriptor(state, resource);
-	const auto  sampler_id     = LoadSamplerDescriptor(state, sampler);
+	EXIT_IF(image_resource.resource_class != IR::ImageResourceClass::Sampled);
+	const auto  image          = LoadImageDescriptor(state, resource, mip);
 	const auto  sampled_image = state.builder.AllocateId();
 	const auto  sampled_type =
 	    state.builder.Type(spv::OpTypeSampledImage, ImageType(state, image_resource));
@@ -194,17 +185,17 @@ uint32_t MakeSampledImage(EmitterState& state, uint32_t resource, uint32_t sampl
 	return sampled_image;
 }
 
-uint32_t StorageImageDescriptorPointer(EmitterState& state, uint32_t resource) {
+uint32_t ImageDescriptorPointer(EmitterState& state, uint32_t resource, uint32_t mip) {
 	const auto& image = state.program.info.images.at(resource);
-	EXIT_IF(image.resource_class != IR::ImageResourceClass::Storage);
+	EXIT_IF(mip >= image.mip_count);
 	const auto kind = IR::DescriptorBindingForImage(image);
 	EXIT_IF(!kind.has_value());
-	const auto array_index  = ResourceForDescriptor(state, *kind, resource);
+	const auto array_index  = ResourceForDescriptor(state, *kind, resource) + mip;
 	const auto pointer_type = state.builder.Type(
 	    spv::OpTypePointer, spv::StorageClassUniformConstant, ImageType(state, image));
 	const auto variable = state.image_variables[IR::ImageBindingIndex(*kind)];
 	return DescriptorElementPointer(state, pointer_type, variable, array_index, *kind, resource,
-	                                "storage image descriptor array was not emitted");
+	                                "image descriptor array was not emitted");
 }
 
 void EmitStorageImageWrite(EmitterState& state, uint32_t resource, uint32_t mip_lod, uint32_t coord,
@@ -214,46 +205,15 @@ void EmitStorageImageWrite(EmitterState& state, uint32_t resource, uint32_t mip_
 	if (!image.atomic) {
 		state.builder.RequireCapability(spv::CapabilityStorageImageWriteWithoutFormat);
 	}
-	const auto kind = IR::DescriptorBindingForImage(image);
-	EXIT_IF(!kind.has_value());
-	const auto array_index = ResourceForDescriptor(state, *kind, resource);
-	const auto image_type  = ImageType(state, image);
-	const auto pointer_type =
-	    state.builder.Type(spv::OpTypePointer, spv::StorageClassUniformConstant, image_type);
-	const auto variable = state.image_variables[IR::ImageBindingIndex(*kind)];
-	const auto LoadAt   = [&](uint32_t array_index) {
-		const auto pointer =
-		    DescriptorElementPointer(state, pointer_type, variable, array_index, *kind, resource,
-		                             "storage image descriptor array was not emitted");
-		const auto descriptor = state.builder.AllocateId();
-		state.builder.AddFunction(spv::OpLoad, image_type, descriptor, pointer);
-		return descriptor;
+	const auto EmitWrite = [&](uint32_t mip) {
+		state.builder.AddFunction(spv::OpImageWrite, LoadImageDescriptor(state, resource, mip),
+		                          coord, texel);
 	};
-	if (image.mip_mode != IR::ImageMipMode::DynamicStorage) {
-		state.builder.AddFunction(spv::OpImageWrite, LoadAt(array_index), coord, texel);
+	if (image.mip_mode != IR::ImageMipMode::Dynamic) {
+		EmitWrite(0);
 		return;
 	}
-	if (image.mip_count == 0u) {
-		ExitDescriptorBindingFailure(state, *kind, resource,
-		                             "dynamic storage image has no mip descriptors");
-	}
-
-	const auto            merge_label = state.builder.AllocateId();
-	std::vector<uint32_t> labels(image.mip_count);
-	std::vector<uint32_t> words {spv::OpSwitch, mip_lod, merge_label};
-	for (uint32_t mip = 0; mip < image.mip_count; mip++) {
-		labels[mip] = state.builder.AllocateId();
-		words.push_back(mip);
-		words.push_back(labels[mip]);
-	}
-	state.builder.AddFunction(spv::OpSelectionMerge, merge_label, spv::SelectionControlMaskNone);
-	state.builder.AddFunction(words);
-	for (uint32_t mip = 0; mip < image.mip_count; mip++) {
-		EmitLabel(state, labels[mip]);
-		state.builder.AddFunction(spv::OpImageWrite, LoadAt(array_index + mip), coord, texel);
-		state.builder.AddFunction(spv::OpBranch, merge_label);
-	}
-	EmitLabel(state, merge_label);
+	EmitImageMipSwitch(state, mip_lod, image.mip_count, 0, EmitWrite);
 }
 
 spv::ExecutionModel ExecutionModelForStage(ShaderType stage) {

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

@@ -3,9 +3,7 @@
 #include "graphics/shader/recompiler/frontend/decode/ImageOps.h"
 
 #include <algorithm>
-#include <atomic>
 #include <bit>
-#include <cstdio>
 
 namespace Libs::Graphics::ShaderRecompiler::Spirv::Emitter {
 namespace {
@@ -86,6 +84,46 @@ uint32_t ZeroF32(EmitterState& state) {
 	return ConstantF32(state, 0);
 }
 
+uint32_t GatherMip(ValueEmitContext& ctx, const IR::Inst& inst, const IR::MemoryInfo& mem,
+                   const IR::Inst& address, const ImageSampleLayout& layout, uint32_t mip_count) {
+	auto& state = ctx.state;
+	const auto Extract = [&](uint32_t word, uint32_t first, uint32_t count) {
+		return EmitBitFieldUExtract(state, word, ConstantU32(state, first),
+		                           ConstantU32(state, count));
+	};
+	const auto LodFixed = [&](uint32_t word, uint32_t first) {
+		return Binary(state, spv::OpFMul, TypeF32(state),
+		              Unary(state, spv::OpConvertUToF, TypeF32(state), Extract(word, first, 12)),
+		              ConstantF32Value(state, 1.0f / 256.0f));
+	};
+	const auto sampler_control = ctx.Arg(inst, 6);
+	const auto preclamp = Binary(state, spv::OpINotEqual, TypeBool(state),
+	                            Extract(sampler_control, 28, 1), ConstantU32(state, 0));
+	const auto half = ConstantF32Value(state, 0.5f);
+	const auto zero = ZeroF32(state);
+	const auto base = Unary(state, spv::OpConvertUToF, TypeF32(state),
+	                        Extract(ctx.Arg(inst, 4), 12, 4));
+	const auto minimum = Binary(state, spv::OpFSub, TypeF32(state),
+	                            LodFixed(ctx.Arg(inst, 3), 8), base);
+	const auto last = ConstantF32Value(state, static_cast<float>(mip_count - 1u));
+	auto lod = Binary(state, spv::OpFAdd, TypeF32(state),
+	                  AddressF32(ctx, mem, address, layout.lod),
+	                  Select(state, TypeF32(state), preclamp, half, zero));
+	lod = EmitGlsl<GLSLstd450FClamp, IR::Type::F32>(
+	    state, lod, LodFixed(ctx.Arg(inst, 5), 0), LodFixed(ctx.Arg(inst, 5), 12));
+	// T# minimum LOD is in physical mip space and applies after the S# view-relative clamp.
+	lod = EmitGlsl<GLSLstd450FMax, IR::Type::F32>(state, lod, minimum);
+	lod = EmitGlsl<GLSLstd450FClamp, IR::Type::F32>(state, lod, zero, last);
+	lod = Binary(state, spv::OpFAdd, TypeF32(state), lod,
+	             Select(state, TypeF32(state), preclamp, zero, half));
+	// The clamped value is nonnegative, so conversion performs the integer mip rounding.
+	const auto mip = EmitUMin32(state, Unary(state, spv::OpConvertFToU, TypeU32(state), lod),
+	                           ConstantU32(state, mip_count - 1u));
+	const auto mip_none = Binary(state, spv::OpIEqual, TypeBool(state),
+	                            Extract(sampler_control, 26, 2), ConstantU32(state, 0));
+	return Select(state, TypeU32(state), mip_none, ConstantU32(state, 0), mip);
+}
+
 uint32_t CubeAxis(EmitterState& state, uint32_t value) {
 	return Binary(state, spv::OpFSub, TypeF32(state), value, ConstantF32(state, 0x3f800000u));
 }
@@ -252,7 +290,7 @@ uint32_t QueryDimensions(ValueEmitContext& ctx, const IR::MemoryInfo& mem,
                          const IR::Inst& address) {
 	const auto  dimension = ctx.state.program.info.images.at(mem.resource).dimension;
 	const auto& info      = ImageDimensionInfoFor(dimension);
-	const auto  image     = LoadSampledImageDescriptor(ctx.state, mem.resource);
+	const auto  image     = LoadImageDescriptor(ctx.state, mem.resource);
 	const auto  size      = ctx.state.builder.AllocateId();
 	if (info.multisampled != 0u) {
 		ctx.state.builder.AddFunction(spv::OpImageQuerySize,
@@ -433,7 +471,7 @@ uint32_t EmitOneDimensionalGatherLz(ValueEmitContext& ctx, const IR::MemoryInfo&
                                     uint32_t coord, Prospero::TextureNumericClass numeric_class) {
 	auto& state = ctx.state;
 	state.builder.RequireCapability(spv::CapabilityImageQuery);
-	const auto image = LoadSampledImageDescriptor(state, mem.resource);
+	const auto image = LoadImageDescriptor(state, mem.resource);
 	const auto width = state.builder.AllocateId();
 	state.builder.AddFunction(spv::OpImageQuerySizeLod, TypeU32(state), width, image,
 	                          ConstantU32(state, 0));
@@ -446,7 +484,8 @@ uint32_t EmitOneDimensionalGatherLz(ValueEmitContext& ctx, const IR::MemoryInfo&
 	                                 Binary(state, spv::OpFMul, TypeF32(state), coord, width_f32),
 	                                 ConstantF32(state, 0x3f000000u)));
 
-	const auto sampled     = MakeSampledImage(state, mem.resource, mem.sampler);
+	const auto sampled = MakeSampledImage(state, mem.resource,
+	                                     LoadSamplerDescriptor(state, mem.sampler));
 	const auto vector_type = ImageVectorType(state, numeric_class, 4);
 	const auto scalar_type = ImageScalarType(state, numeric_class);
 	const auto component =
@@ -558,7 +597,8 @@ void EmitImage(ValueEmitContext& ctx, const IR::Inst& inst) {
 	if (op == IR::ValueOpcode::ImageQueryLod) {
 		state.builder.RequireCapability(spv::CapabilityImageQuery);
 		const auto dimension = image.dimension;
-		const auto sampled   = MakeSampledImage(state, mem.resource, mem.sampler);
+		const auto sampled = MakeSampledImage(state, mem.resource,
+		                                     LoadSamplerDescriptor(state, mem.sampler));
 		const auto lod       = state.builder.AllocateId();
 		state.builder.AddFunction(
 		    spv::OpImageQueryLod, TypeF32Vector(state, 2), lod, sampled,
@@ -588,7 +628,7 @@ void EmitImage(ValueEmitContext& ctx, const IR::Inst& inst) {
 		    EmitValueOrDefaultIfCondition(
 		        state, condition, TypeU32Vector(state, 4), ConstantU32CompositeZero(state, 4),
 		        [&]() {
-			        const auto descriptor = LoadSampledImageDescriptor(state, mem.resource);
+			        const auto descriptor = LoadImageDescriptor(state, mem.resource);
 			        const auto color      = state.builder.AllocateId();
 			        const auto coord      = CoordU32(ctx, mem, *address, dimension);
 			        if (dimension_info.multisampled != 0u) {
@@ -612,7 +652,7 @@ void EmitImage(ValueEmitContext& ctx, const IR::Inst& inst) {
 		const auto dimension  = image.dimension;
 		EmitIfCondition(state, ctx.Arg(inst, 3), [&]() {
 			const auto mip_lod =
-			    state.program.info.images[mem.resource].mip_mode == IR::ImageMipMode::DynamicStorage
+			    state.program.info.images[mem.resource].mip_mode == IR::ImageMipMode::Dynamic
 			        ? LodU32(ctx, mem, *address, dimension)
 			        : 0u;
 			const auto coord = CoordU32(ctx, mem, *address, dimension);
@@ -635,13 +675,6 @@ void EmitImage(ValueEmitContext& ctx, const IR::Inst& inst) {
 		if (op == IR::ValueOpcode::ImageGatherRaw) {
 			const auto coord = CoordF32(ctx, mem, *address, layout.coord,
 			                            dimension_info.coordinate_components, image.cube);
-			if (HasFlag(mem, Decoder::ImageSampleFlagLod)) {
-				static std::atomic_flag warned = ATOMIC_FLAG_INIT;
-				if (!warned.test_and_set(std::memory_order_relaxed)) {
-					std::fputs("Warning: approximating IMAGE_GATHER4_L at mip level 0; explicit LOD is ignored.\n",
-					           stderr);
-				}
-			}
 			if (dimension == ImageDimension::Dim1D) {
 				if (dref || !HasFlag(mem, Decoder::ImageSampleFlagLevelZero) ||
 				    HasFlag(mem, Decoder::ImageSampleFlagOffset) ||
@@ -658,44 +691,48 @@ void EmitImage(ValueEmitContext& ctx, const IR::Inst& inst) {
 				ctx.Fail(inst, "has an unsupported 1D-array gather");
 				return;
 			}
-			const auto            sampled = MakeSampledImage(state, mem.resource, mem.sampler);
-			const auto            sample  = state.builder.AllocateId();
-			std::vector<uint32_t> words;
+			const auto result_numeric_class = dref ? Prospero::TextureNumericClass::Float
+			                                       : numeric_class;
+			const auto result_type = ImageVectorType(state, result_numeric_class, 4);
+			uint32_t component_or_dref;
 			if (dref) {
-				auto dref_value = ZeroF32(state);
-				if (layout.dref != NoImageComponent) {
-					dref_value = AddressF32(ctx, mem, *address, layout.dref);
-				}
-				words = {spv::OpImageDrefGather,
-				         TypeF32Vector(state, 4),
-				         sample,
-				         sampled,
-				         coord,
-				         dref_value};
+				component_or_dref = layout.dref != NoImageComponent
+				                        ? AddressF32(ctx, mem, *address, layout.dref)
+				                        : ZeroF32(state);
 			} else {
-				uint32_t component = 0;
-				if (ImageConversionFormat(state, mem).format == Prospero::BufferFormat::kInvalid) {
-					component = ImageGatherComponent(mem.dmask);
-				}
-				words = {spv::OpImageGather,
-				         ImageVectorType(state, numeric_class, 4),
-				         sample,
-				         sampled,
-				         coord,
-				         ConstantU32(state, component)};
+				component_or_dref = ConstantU32(
+				    state, ImageConversionFormat(state, mem).format == Prospero::BufferFormat::kInvalid
+				               ? ImageGatherComponent(mem.dmask) : 0u);
 			}
+			uint32_t operand_mask = 0;
+			uint32_t offset = 0;
 			if (HasFlag(mem, Decoder::ImageSampleFlagGatherHorizontal)) {
-				words.push_back(spv::ImageOperandsConstOffsetsMask);
-				words.push_back(HorizontalOffsets(state, dimension));
+				operand_mask = spv::ImageOperandsConstOffsetsMask;
+				offset = HorizontalOffsets(state, dimension);
 			} else if (layout.offset != NoImageComponent) {
-				words.push_back(spv::ImageOperandsOffsetMask);
-				words.push_back(PackedOffset(ctx, mem, *address, layout, dimension));
-			}
-			state.builder.AddFunction(words);
-			auto result_numeric_class = numeric_class;
-			if (dref) {
-				result_numeric_class = Prospero::TextureNumericClass::Float;
+				operand_mask = spv::ImageOperandsOffsetMask;
+				offset = PackedOffset(ctx, mem, *address, layout, dimension);
 			}
+			const auto sampler_id = LoadSamplerDescriptor(state, mem.sampler);
+			const auto EmitGather = [&](uint32_t mip) {
+				const auto sampled = MakeSampledImage(state, mem.resource, sampler_id, mip);
+				const auto sample = state.builder.AllocateId();
+				std::vector<uint32_t> words {
+				    dref ? spv::OpImageDrefGather : spv::OpImageGather, result_type,
+				    sample, sampled, coord, component_or_dref};
+				if (operand_mask != 0u) {
+					words.push_back(operand_mask);
+					words.push_back(offset);
+				}
+				state.builder.AddFunction(words);
+				return sample;
+			};
+			const auto sample = image.mip_mode == IR::ImageMipMode::Dynamic && image.mip_count > 1u
+			                        ? EmitImageMipSwitch(
+			                              state, GatherMip(ctx, inst, mem, *address, layout,
+			                                               image.mip_count),
+			                              image.mip_count, result_type, EmitGather)
+			                        : EmitGather(0);
 			ctx.Define(inst, ResultVector(ctx, UnpackImageGather(ctx, mem, sample),
 			                              result_numeric_class, false, mem, true));
 			return;
@@ -738,13 +775,14 @@ void EmitImage(ValueEmitContext& ctx, const IR::Inst& inst) {
 			operand_mask |= spv::ImageOperandsBiasMask;
 			operands.push_back(AddressF32(ctx, mem, *address, layout.bias));
 		}
+		const auto sampler_id = LoadSamplerDescriptor(state, mem.sampler);
 		const auto EmitSample = [&](uint32_t resource) {
 			const auto& candidate = state.program.info.images[resource];
 			const auto coord =
 			    CoordF32(ctx, mem, *address, layout.coord,
 			             ImageDimensionInfoFor(candidate.dimension).coordinate_components,
 			             candidate.cube);
-			const auto            sampled = MakeSampledImage(state, resource, mem.sampler);
+			const auto            sampled = MakeSampledImage(state, resource, sampler_id);
 			const auto            sample  = state.builder.AllocateId();
 			std::vector<uint32_t> sample_operands {result_type, sample, sampled, coord};
 			if (dref) {
@@ -874,7 +912,7 @@ void EmitImage(ValueEmitContext& ctx, const IR::Inst& inst) {
 			               spv::OpTypePointer, spv::StorageClassImage,
 			               image.atomic64 ? TypeScalarU64(state) : TypeU32(state));
 			           state.builder.AddFunction(spv::OpImageTexelPointer, pointer_type, pointer,
-			                                     StorageImageDescriptorPointer(state, mem.resource),
+			                                     ImageDescriptorPointer(state, mem.resource),
 			                                     CoordU32(ctx, mem, *address, dimension),
 			                                     ConstantU32(state, 0));
 			           if (op == IR::ValueOpcode::ImageAtomicFMin32 ||

src/graphics/shader/recompiler/backend/spirv/spirvEmitterInternal.h

@@ -19,6 +19,7 @@
 #include <map>
 #include <spirv/unified1/GLSL.std.450.h>
 #include <string>
+#include <type_traits>
 #include <unordered_map>
 #include <utility>
 #include <vector>
@@ -314,13 +315,14 @@ uint32_t ImageType(EmitterState& state, const IR::ImageResource& image);
 
 uint32_t ImageViewSizeType(EmitterState& state, ImageDimension dimension);
 
-uint32_t LoadSampledImageDescriptor(EmitterState& state, uint32_t resource);
+uint32_t ImageDescriptorPointer(EmitterState& state, uint32_t resource, uint32_t mip = 0);
+
+uint32_t LoadImageDescriptor(EmitterState& state, uint32_t resource, uint32_t mip = 0);
 
 uint32_t LoadSamplerDescriptor(EmitterState& state, uint32_t sampler);
 
-uint32_t MakeSampledImage(EmitterState& state, uint32_t resource, uint32_t sampler);
-
-uint32_t StorageImageDescriptorPointer(EmitterState& state, uint32_t resource);
+uint32_t MakeSampledImage(EmitterState& state, uint32_t resource, uint32_t sampler_id,
+                          uint32_t mip = 0);
 
 void EmitStorageImageWrite(EmitterState& state, uint32_t resource, uint32_t mip_lod, uint32_t coord,
                            uint32_t texel);
@@ -514,6 +516,45 @@ uint32_t ConstantDeviceAddress(EmitterState& state, uint64_t value);
 uint32_t DeviceAddressFromWords(EmitterState& state, uint32_t low, uint32_t high);
 
 // These templates accept local lambdas from several emitter translation units.
+template <typename Fn>
+auto EmitImageMipSwitch(EmitterState& state, uint32_t mip_lod, uint32_t mip_count,
+                        uint32_t result_type, Fn&& emit) {
+	constexpr bool has_result = !std::is_void_v<std::invoke_result_t<Fn, uint32_t>>;
+	EXIT_IF(mip_count == 0u);
+	const auto merge_label = state.builder.AllocateId();
+	std::vector<uint32_t> labels(mip_count);
+	std::vector<uint32_t> words {spv::OpSwitch, mip_lod, merge_label};
+	for (uint32_t mip = 0; mip < mip_count; mip++) {
+		labels[mip] = state.builder.AllocateId();
+		words.push_back(mip);
+		words.push_back(labels[mip]);
+	}
+	if constexpr (has_result) {
+		words[2] = labels.front();
+	}
+	state.builder.AddFunction(spv::OpSelectionMerge, merge_label, spv::SelectionControlMaskNone);
+	state.builder.AddFunction(words);
+	std::vector<uint32_t> phi;
+	if constexpr (has_result) {
+		phi = {spv::OpPhi, result_type, state.builder.AllocateId()};
+	}
+	for (uint32_t mip = 0; mip < mip_count; mip++) {
+		EmitLabel(state, labels[mip]);
+		if constexpr (has_result) {
+			phi.push_back(emit(mip));
+			phi.push_back(state.current_label);
+		} else {
+			emit(mip);
+		}
+		state.builder.AddFunction(spv::OpBranch, merge_label);
+	}
+	EmitLabel(state, merge_label);
+	if constexpr (has_result) {
+		state.builder.AddFunction(phi);
+		return phi[2];
+	}
+}
+
 template <typename Fn>
 void EmitIfCondition(EmitterState& state, uint32_t condition, Fn&& fn) {
 	const auto then_label  = state.builder.AllocateId();

src/graphics/shader/recompiler/frontend/translate/Memory.cpp

@@ -708,8 +708,16 @@ void Translator::IMAGE_GATHER(const Decoder::Instruction& inst) {
 	const auto resource = GetImageResource(memory);
 	const auto sampler  = GetSamplerResource(memory);
 	const auto address  = MakeImageAddress(inst, MemorySourceAt(inst, 0));
-	const auto result   = ir.Emit(IR::ValueOpcode::ImageGatherRaw, {resource, sampler, address},
-	                              AddMemoryInfo(memory, inst.pc));
+	const bool has_lod = (memory.image_sample_flags & Decoder::ImageSampleFlagLod) != 0u;
+	// LOD selection consumes these words on the GPU after descriptor handles are stripped.
+	const auto result = ir.Emit(
+	    IR::ValueOpcode::ImageGatherRaw,
+	    {resource, sampler, address,
+	     has_lod ? resource.Instruction()->Arg(1) : IR::Value(0u),
+	     has_lod ? resource.Instruction()->Arg(3) : IR::Value(0u),
+	     has_lod ? sampler.Instruction()->Arg(1) : IR::Value(0u),
+	     has_lod ? sampler.Instruction()->Arg(2) : IR::Value(0u)},
+	    AddMemoryInfo(memory, inst.pc));
 	for (uint32_t index = 0; index < memory.data_dwords; index++) {
 		WriteOperand(OffsetOperand(inst.dst, index),
 		             ir.Emit(IR::ValueOpcode::CompositeExtractU32x4, {result, IR::Value(index)}));

src/graphics/shader/recompiler/ir/ShaderIR.h

@@ -114,7 +114,7 @@ struct BufferResource {
 	bool operator==(const BufferResource& other) const = default;
 };
 
-enum class ImageMipMode { None, DynamicStorage };
+enum class ImageMipMode { None, Dynamic };
 
 constexpr uint32_t ShaderImageIdentitySwizzle = 0x00000facu;
 
@@ -151,6 +151,7 @@ struct SamplerResource {
 	bool     force_point_filtering = false;
 	bool     depth_compare         = false;
 	bool     integer_border        = false;
+	bool     gather_lod            = false;
 
 	bool operator==(const SamplerResource& other) const = default;
 };

src/graphics/shader/recompiler/ir/opcodes/ValueOpcodes.inc

@@ -297,7 +297,7 @@ VALUE_OPCODE(ImageQueryLod, U32x4, ImageResource, SamplerResource, ImageAddress)
 VALUE_OPCODE(ImageRead, U32x4, ImageResource, ImageAddress, U1)
 VALUE_OPCODE(ImageWrite, Void, ImageResource, ImageAddress, U32x4, U1)
 VALUE_OPCODE(ImageSampleRaw, U32x4, ImageResource, SamplerResource, ImageAddress)
-VALUE_OPCODE(ImageGatherRaw, U32x4, ImageResource, SamplerResource, ImageAddress)
+VALUE_OPCODE(ImageGatherRaw, U32x4, ImageResource, SamplerResource, ImageAddress, U32, U32, U32, U32)
 VALUE_OPCODE(ImageAtomicCompareSwap32, U32, ImageResource, ImageAddress, U32, U32, U1)
 VALUE_OPCODE(ImageAtomicSwap32, U32, ImageResource, ImageAddress, U32, U1)
 VALUE_OPCODE(ImageAtomicIAdd32, U32, ImageResource, ImageAddress, U32, U1)

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

@@ -126,7 +126,7 @@ void AllocateBindings(Program& program, uint32_t push_data_start_dword) {
 			EXIT("shader binding layout failed: image %u has an unmapped binding class", i);
 		}
 		auto&      resources = image_groups[group];
-		const auto dynamic   = program.info.images[i].mip_mode == ImageMipMode::DynamicStorage;
+		const auto dynamic   = program.info.images[i].mip_mode == ImageMipMode::Dynamic;
 		const auto count     = dynamic ? program.info.images[i].mip_count : 1u;
 		if (count == 0u || (!dynamic && program.info.images[i].mip_count != 1u)) {
 			EXIT("shader binding layout failed: image %u has invalid specialized mip count %u", i,

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

@@ -124,8 +124,8 @@ bool DescriptorIsCube(const DescriptorValue& descriptor) {
 	       Prospero::ImageType::kCube;
 }
 
-uint32_t StorageMipCount(const ImageResource& image, const DescriptorValue& descriptor) {
-	if (image.mip_mode != ImageMipMode::DynamicStorage || NullImageDescriptor(descriptor)) {
+uint32_t ImageMipCount(const ImageResource& image, const DescriptorValue& descriptor) {
+	if (image.mip_mode != ImageMipMode::Dynamic || NullImageDescriptor(descriptor)) {
 		return 1;
 	}
 	const auto base = (descriptor.dwords[3] >> 12u) & 0xfu;
@@ -435,10 +435,10 @@ static bool BuildResourceSpecialization(const ResourcePlan& program, ResourceSna
 		    (base.atomic && base.resource_class != ImageResourceClass::Storage)) {
 			return SpecializationFail(fmt::format("image resource {} has an invalid class", i));
 		}
-		image.mip_count = StorageMipCount(base, descriptor);
+		image.mip_count = ImageMipCount(base, descriptor);
 		if (image.mip_count == 0u) {
 			return SpecializationFail(
-			    fmt::format("storage image descriptor {} has an invalid mip range", i));
+			    fmt::format("image descriptor {} has an invalid mip range", i));
 		}
 		if (NullImageDescriptor(descriptor)) {
 			image.numeric_class = base.atomic ? Prospero::TextureNumericClass::Uint
@@ -1077,6 +1077,16 @@ bool MaterializeResources(const ResourcePlan& program, const SrtRuntime& runtime
 		if (!evaluate(program.info.samplers[i].source, snapshot.samplers[i])) {
 			return false;
 		}
+		if (program.info.samplers[i].gather_lod) {
+			const auto control = snapshot.samplers[i].dwords[2];
+			const auto filter = (control >> 26u) & 3u;
+			// MipNone always selects the base level. Explicit point gathers currently require
+			// encoded-zero primary and secondary bias; linear primary-mip selection is unsupported.
+			if (filter > 1u || (filter == 1u && (control & 0xfffffu) != 0u)) {
+				return SpecializationFail(
+				    "explicit-LOD gather requires mip filtering None or Point with zero LOD biases");
+			}
+		}
 	}
 	snapshot.user_data.assign(runtime.user_data.begin(), runtime.user_data.end());
 	return BuildResourceSpecialization(program, snapshot, specialization);

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

@@ -1727,9 +1727,11 @@ private:
 		const auto resource_class = ImageOpcodeInfoOf(op).resource_class;
 		const bool atomic64 = ImageOpcodeInfoOf(op).access == ImageAccess::Atomic &&
 		                      memory.data_bits == 64u;
-		const auto mip   = resource_class == ImageResourceClass::Storage && memory.image_has_mip
-		                       ? ImageMipMode::DynamicStorage
-		                       : ImageMipMode::None;
+		const bool dynamic_mip =
+		    (resource_class == ImageResourceClass::Storage && memory.image_has_mip) ||
+		    (op == ValueOpcode::ImageGatherRaw &&
+		     (memory.image_sample_flags & Decoder::ImageSampleFlagLod) != 0u);
+		const auto mip = dynamic_mip ? ImageMipMode::Dynamic : ImageMipMode::None;
 		const bool depth = (memory.image_sample_flags & Decoder::ImageSampleFlagCompare) != 0;
 		for (uint32_t i = 0; i < m_info.images.size(); i++) {
 			auto& image = m_info.images[i];
@@ -1939,6 +1941,9 @@ private:
 			if (sampler == UINT32_MAX) {
 				Fail(flags.pc, "sampler resource limit exceeded");
 			}
+			m_info.samplers[sampler].gather_lod |=
+			    op == ValueOpcode::ImageGatherRaw &&
+			    (memory.image_sample_flags & Decoder::ImageSampleFlagLod) != 0u;
 			AddHandlePatch(sampler_handle, sampler, flags.pc);
 			AddSampledPair(resource, sampler, flags.pc);
 		}