Vulkan: compile compute shaders with rslc, decode textures on the GPU again

The compute header comes back for the decoders, and compute shaders and
GPU texture decoding are reported as supported once more. The core
option still decides whether textures are decoded on the GPU.

Source/Core/VideoBackends/Vulkan/ShaderCompiler.cpp

@@ -63,6 +63,29 @@ static const char SHADER_HEADER[] = R"(
   #define gl_VertexID gl_VertexIndex
   #define gl_InstanceID gl_InstanceIndex
 )";
+static const char COMPUTE_SHADER_HEADER[] = R"(
+  // Target GLSL 4.5.
+  #version 450 core
+  // All resources are packed into one descriptor set for compute.
+  #define UBO_BINDING(packing, x) layout(packing, set = 0, binding = (x - 1))
+  #define SAMPLER_BINDING(x) layout(set = 0, binding = (1 + x))
+  #define TEXEL_BUFFER_BINDING(x) layout(set = 0, binding = (9 + x))
+  #define IMAGE_BINDING(format, x) layout(format, set = 0, binding = (11 + x))
+
+  // hlsl to glsl function translation
+  #define API_VULKAN 1
+  #define float2 vec2
+  #define float3 vec3
+  #define float4 vec4
+  #define uint2 uvec2
+  #define uint3 uvec3
+  #define uint4 uvec4
+  #define int2 ivec2
+  #define int3 ivec3
+  #define int4 ivec4
+  #define frac fract
+  #define lerp mix
+)";
 /* The stage's full text: the header, then the generator's source. Subgroup
  * operations are not offered to the generators: rslc has no form of them. */
 static std::string GetShaderCode(std::string_view source, std::string_view header)
@@ -102,7 +125,8 @@ static std::optional<SPIRVCodeVector> Compile(std::string_view source_code, enum
   char err[1024];
   struct rslc_opts opts;
   struct rslc_result result;
-  std::string source = GetShaderCode(source_code, SHADER_HEADER);
+  std::string source = GetShaderCode(
+      source_code, stage == RSLC_STAGE_COMPUTE ? COMPUTE_SHADER_HEADER : SHADER_HEADER);
   std::optional<SPIRVCodeVector> spv;
 
   memset(&opts, 0, sizeof(opts));
@@ -138,10 +162,9 @@ std::optional<SPIRVCodeVector> CompileFragmentShader(std::string_view source_cod
   return Compile(source_code, RSLC_STAGE_FRAGMENT, "ps");
 }
 
-/* rslc has no compute stage yet: GPU texture decoding falls back to the CPU. */
 std::optional<SPIRVCodeVector> CompileComputeShader(std::string_view source_code,
                                                     VideoCommon::ShaderIncluder* shader_includer)
 {
-  return std::nullopt;
+  return Compile(source_code, RSLC_STAGE_COMPUTE, "cs");
 }
 }  // namespace Vulkan::ShaderCompiler

Source/Core/VideoBackends/Vulkan/VulkanContext.cpp

@@ -428,9 +428,8 @@ void VulkanContext::PopulateBackendInfo(BackendInfo* backend_info)
   backend_info->bSupportsPaletteConversion = true;          // Assumed support.
   backend_info->bSupportsClipControl = true;                // Assumed support.
   backend_info->bSupportsMultithreading = true;             // Assumed support.
-  // rslc has no compute stage yet.
-  backend_info->bSupportsComputeShaders = false;
-  backend_info->bSupportsGPUTextureDecoding = false;
+  backend_info->bSupportsComputeShaders = true;             // Assumed support.
+  backend_info->bSupportsGPUTextureDecoding = true;         // Assumed support.
   backend_info->bSupportsBitfield = true;                   // Assumed support.
   backend_info->bSupportsPartialDepthCopies = true;         // Assumed support.
   backend_info->bSupportsShaderBinaries = true;             // Assumed support.