Approximate explicit-LOD texture gathers at mip zero

Credits:
YuhiAida (@YuhiAida):
https://github.com/KytyPS5/KytyPS5/pull/588
https://github.com/KytyPS5/KytyPS5/pull/589
https://github.com/KytyPS5/KytyPS5/pull/655
frans (@francoisatt):
https://github.com/KytyPS5/KytyPS5/pull/590
BlackCAT (@psnwd):
https://github.com/KytyPS5/KytyPS5/pull/613
shadowbeat070 (@shadowbeat070):
https://github.com/KytyPS5/KytyPS5/pull/654
Pouare514 (@Pouare514):
https://github.com/KytyPS5/KytyPS5/pull/29
https://github.com/KytyPS5/KytyPS5/pull/32

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

@@ -3,7 +3,9 @@
 #include "graphics/shader/recompiler/frontend/decode/ImageOps.h"
 
 #include <algorithm>
+#include <atomic>
 #include <bit>
+#include <cstdio>
 
 namespace Libs::Graphics::ShaderRecompiler::Spirv::Emitter {
 namespace {
@@ -646,6 +648,13 @@ void EmitImage(ValueEmitContext& ctx, const IR::Inst& inst) {
 		const auto coord =
 		    CoordF32(ctx, mem, *address, layout.coord, dimension_info.coordinate_components);
 		if (op == IR::ValueOpcode::ImageGatherRaw) {
+			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) ||

src/graphics/shader/recompiler/frontend/decode/ImageOps.cpp

@@ -175,6 +175,7 @@ constexpr MimgSampleInfo MIMG_SAMPLE_OPCODE_LIST[] = {
 };
 
 constexpr MimgGatherInfo MIMG_GATHER_OPCODE_LIST[] = {
+    {0x44u, Opcode::IMAGE_GATHER4_L, ImageSampleFlagLod},
     {0x47u, Opcode::IMAGE_GATHER4_LZ, ImageSampleFlagLevelZero},
     {0x48u, Opcode::IMAGE_GATHER4_C, ImageSampleFlagCompare},
     {0x4fu, Opcode::IMAGE_GATHER4_C_LZ,

src/graphics/shader/recompiler/frontend/decode/ShaderDecoder.cpp

@@ -144,6 +144,7 @@ std::string FormatMimg(const Instruction& inst) {
 	}
 	switch (inst.opcode) {
 		case Opcode::IMAGE_SAMPLE:
+		case Opcode::IMAGE_GATHER4_L:
 		case Opcode::IMAGE_GATHER4_LZ:
 		case Opcode::IMAGE_GATHER4_C:
 		case Opcode::IMAGE_GATHER4_C_LZ:
@@ -580,6 +581,7 @@ std::string InstructionToString(const Instruction& inst) {
 		case Opcode::IMAGE_LOAD_MIP:
 		case Opcode::IMAGE_GET_RESINFO:
 		case Opcode::IMAGE_GET_LOD:
+		case Opcode::IMAGE_GATHER4_L:
 		case Opcode::IMAGE_GATHER4_LZ:
 		case Opcode::IMAGE_GATHER4_C:
 		case Opcode::IMAGE_GATHER4_C_LZ:

src/graphics/shader/recompiler/frontend/decode/ShaderDecoder.h

@@ -559,6 +559,7 @@ enum class Opcode {
 	IMAGE_ATOMIC_OR,
 	IMAGE_ATOMIC_XOR,
 	IMAGE_SAMPLE,
+	IMAGE_GATHER4_L,
 	IMAGE_GATHER4_LZ,
 	IMAGE_GATHER4_C,
 	IMAGE_GATHER4_C_LZ,

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

@@ -1034,6 +1034,7 @@ bool Translator::EmitMemory(const Decoder::Instruction& inst) {
 		case Decoder::Opcode::IMAGE_STORE:
 		case Decoder::Opcode::IMAGE_STORE_MIP: return IMAGE_STORE(inst);
 		case Decoder::Opcode::IMAGE_SAMPLE: return IMAGE_SAMPLE(inst);
+		case Decoder::Opcode::IMAGE_GATHER4_L:
 		case Decoder::Opcode::IMAGE_GATHER4_LZ:
 		case Decoder::Opcode::IMAGE_GATHER4_C:
 		case Decoder::Opcode::IMAGE_GATHER4_C_LZ:

tests/ShaderRecompilerComputeTests.cpp

@@ -12271,7 +12271,7 @@ public:
     return ret;
   }
 
-  vk::Sampler CreateNearestSampler(const char *shader_name) {
+  vk::Sampler CreateNearestSampler(const char *shader_name, u32 mip_levels = 1) {
     vk::SamplerCreateInfo sampler_info{};
     sampler_info.sType = vk::StructureType::eSamplerCreateInfo;
     sampler_info.magFilter = vk::Filter::eNearest;
@@ -12281,7 +12281,7 @@ public:
     sampler_info.addressModeV = vk::SamplerAddressMode::eClampToEdge;
     sampler_info.addressModeW = vk::SamplerAddressMode::eClampToEdge;
     sampler_info.minLod = 0.0f;
-    sampler_info.maxLod = 0.0f;
+    sampler_info.maxLod = static_cast<float>(mip_levels - 1u);
     vk::Sampler sampler = nullptr;
     RequireVk(shader_name, "dispatch",
               m_device.createSampler(&sampler_info, nullptr, &sampler),
@@ -15484,7 +15484,7 @@ void RunCase(VulkanHarness *vulkan, const TestCase &test) {
         vk::ImageLayout::eGeneral);
   }
   if (needs_sampler) {
-    sampler = vulkan->CreateNearestSampler(test.name);
+    sampler = vulkan->CreateNearestSampler(test.name, sampled_image.mip_levels);
   }
 
   vulkan->Dispatch(test, compiled, buffer, needs_gds ? &gds_buffer : nullptr,
@@ -25001,6 +25001,34 @@ TestCase ImageSampleAndGather() {
   return test;
 }
 
+TestCase ImageGatherLodApproximatesLevelZero() {
+  using O = ShaderOpcode;
+  std::vector<u32> code;
+  AppendVMovLiteral(&code, 20, 0x3f000000u);
+  AppendVMovLiteral(&code, 21, 0x3f000000u);
+  AppendVMovLiteral(&code, 22, 0x3f800000u);
+  code.push_back(EncodeMimg0(0x44, 0x1));
+  code.push_back(EncodeMimg1(0, 20));
+  code.push_back(EncodeMimg0(0x24, 0x1));
+  code.push_back(EncodeMimg1(4, 20));
+  for (u32 i = 0; i < 5u; i++) {
+    AppendStoreVgpr(&code, i, i);
+  }
+  AppendEnd(&code);
+
+  TestCase test;
+  test.name = "ImageGatherLodApproximatesLevelZero";
+  test.code = std::move(code);
+  test.opcodes = {O::V_MOV_B32, O::IMAGE_GATHER4_L, O::IMAGE_SAMPLE,
+                  O::BUFFER_STORE_DWORD, O::S_ENDPGM};
+  // Explicit sampling proves mip 1 is accessible; the gather must still read mip 0.
+  test.expected = {0x3f800000u, 0x3f800000u, 0x3f800000u, 0x3f800000u, 0x41000000u};
+  test.sampled_image_rgba_mips = {std::vector<u32>(4 * 4 * 4, 0x3f800000u),
+                                 std::vector<u32>(2 * 2 * 4, 0x41000000u)};
+  test.required_spirv = {"OpImageGather", "OpImageSampleExplicitLod"};
+  return test;
+}
+
 TestCase ImageD16GatherPacksHalfPairs() {
   using O = ShaderOpcode;
 
@@ -26575,6 +26603,7 @@ std::vector<TestCase> MakeCases() {
   AddCase(ImageGetResinfoDmaskWidthHeight);
   AddCase(ImageGetResinfoDmaskMipLevels);
   AddCase(ImageSampleAndGather);
+  AddCase(ImageGatherLodApproximatesLevelZero);
   AddCase(ImageD16GatherPacksHalfPairs);
   AddCase(ImageSampleA16SamplerCoordsOnGpu);
   AddCase(ImageSampleOpcodeAliasUsesNormalCoords);
@@ -31166,6 +31195,7 @@ int main(int argc, char **argv) {
     RunCase(&vulkan, BranchVccnzUsesWaveMask());
     RunCase(&vulkan, BranchVccnzUsesCarryProducedWaveMask());
     RunCase(&vulkan, ImageSampleAndGather());
+    RunCase(&vulkan, ImageGatherLodApproximatesLevelZero());
     RunCase(&vulkan, SharedReturnKeepsSelectedValues());
     return 0;
   }