Vulkan: Move xfb position decl to translator in extension path

include/GLSLANG/ShaderLang.h

@@ -26,7 +26,7 @@
 
 // Version number for shader translation API.
 // It is incremented every time the API changes.
-#define ANGLE_SH_VERSION 249
+#define ANGLE_SH_VERSION 250
 
 enum ShShaderSpec
 {
@@ -348,9 +348,13 @@ const ShCompileOptions SH_FORCE_SHADER_PRECISION_HIGHP_TO_MEDIUMP = UINT64_C(1)
 // Allow compiler to use specialization constant to do pre-rotation and y flip.
 const ShCompileOptions SH_USE_SPECIALIZATION_CONSTANT = UINT64_C(1) << 58;
 
-// Ask compiler to generate transform feedback emulation support code.
+// Ask compiler to generate Vulkan transform feedback emulation support code.
 const ShCompileOptions SH_ADD_VULKAN_XFB_EMULATION_SUPPORT_CODE = UINT64_C(1) << 59;
 
+// Ask compiler to generate Vulkan transform feedback support code when using the
+// VK_EXT_transform_feedback extension.
+const ShCompileOptions SH_ADD_VULKAN_XFB_EXTENSION_SUPPORT_CODE = UINT64_C(1) << 60;
+
 // Defines alternate strategies for implementing array index clamping.
 enum ShArrayIndexClampingStrategy
 {
@@ -873,12 +877,15 @@ extern const char kAtomicCountersBlockName[];
 // Line raster emulation varying
 extern const char kLineRasterEmulationPosition[];
 
-// Transform feedback emulation helper function
+// Transform feedback emulation support
 extern const char kXfbEmulationGetOffsetsFunctionName[];
 extern const char kXfbEmulationBufferBlockName[];
 extern const char kXfbEmulationBufferName[];
 extern const char kXfbEmulationBufferFieldName[];
 
+// Transform feedback extension support
+extern const char kXfbExtensionPositionOutName[];
+
 }  // namespace vk
 
 namespace mtl

src/compiler/translator/ShaderLang.cpp

@@ -797,6 +797,8 @@ const char kXfbEmulationBufferBlockName[]        = "ANGLEXfbBuffer";
 const char kXfbEmulationBufferName[]             = "ANGLEXfb";
 const char kXfbEmulationBufferFieldName[]        = "xfbOut";
 
+const char kXfbExtensionPositionOutName[] = "ANGLEXfbPosition";
+
 }  // namespace vk
 
 }  // namespace sh

src/compiler/translator/TranslatorVulkan.cpp

@@ -481,6 +481,48 @@ ANGLE_NO_DISCARD bool AddXfbEmulationSupport(TCompiler *compiler,
     return compiler->validateAST(root);
 }
 
+ANGLE_NO_DISCARD bool AddXfbExtensionSupport(TCompiler *compiler,
+                                             TIntermBlock *root,
+                                             TSymbolTable *symbolTable,
+                                             const DriverUniform *driverUniforms)
+{
+    // Generate the following output varying declaration used to capture transform feedback output
+    // from gl_Position, as it can't be captured directly due to changes that are applied to it for
+    // clip-space correction and pre-rotation.
+    //
+    //     out vec4 ANGLEXfbPosition;
+
+    const TType *vec4Type = nullptr;
+
+    switch (compiler->getShaderType())
+    {
+        case GL_VERTEX_SHADER:
+            vec4Type = StaticType::Get<EbtFloat, EbpHigh, EvqVertexOut, 4, 1>();
+            break;
+        case GL_TESS_EVALUATION_SHADER_EXT:
+            vec4Type = StaticType::Get<EbtFloat, EbpHigh, EvqTessEvaluationOut, 4, 1>();
+            break;
+        case GL_GEOMETRY_SHADER_EXT:
+            vec4Type = StaticType::Get<EbtFloat, EbpHigh, EvqGeometryOut, 4, 1>();
+            break;
+        default:
+            UNREACHABLE();
+    }
+
+    TVariable *varyingVar =
+        new TVariable(symbolTable, ImmutableString(vk::kXfbExtensionPositionOutName), vec4Type,
+                      SymbolType::AngleInternal);
+
+    TIntermDeclaration *varyingDecl = new TIntermDeclaration();
+    varyingDecl->appendDeclarator(new TIntermSymbol(varyingVar));
+
+    // Insert the varying declaration before the first function.
+    const size_t firstFunctionIndex = FindFirstFunctionDefinitionIndex(root);
+    root->insertChildNodes(firstFunctionIndex, {varyingDecl});
+
+    return compiler->validateAST(root);
+}
+
 ANGLE_NO_DISCARD bool InsertFragCoordCorrection(TCompiler *compiler,
                                                 ShCompileOptions compileOptions,
                                                 TIntermBlock *root,
@@ -829,8 +871,14 @@ bool TranslatorVulkan::translateImpl(TIntermBlock *root,
 
     if (gl::ShaderTypeSupportsTransformFeedback(packedShaderType))
     {
-        // Add a macro to declare transform feedback buffers.
-        sink << "@@ XFB-DECL @@\n\n";
+        if (compileOptions & SH_ADD_VULKAN_XFB_EXTENSION_SUPPORT_CODE)
+        {
+            // Add support code for transform feedback extension.
+            if (!AddXfbExtensionSupport(this, root, &getSymbolTable(), driverUniforms))
+            {
+                return false;
+            }
+        }
 
         // Append a macro for transform feedback substitution prior to modifying depth.
         if (!AppendTransformFeedbackOutputToMain(this, root, &getSymbolTable()))

src/libANGLE/renderer/vulkan/ShaderVk.cpp

@@ -87,7 +87,11 @@ std::shared_ptr<WaitableCompileEvent> ShaderVk::compile(const gl::Context *conte
         compileOptions |= SH_ADD_PRE_ROTATION;
     }
 
-    if (contextVk->getFeatures().emulateTransformFeedback.enabled)
+    if (contextVk->getFeatures().supportsTransformFeedbackExtension.enabled)
+    {
+        compileOptions |= SH_ADD_VULKAN_XFB_EXTENSION_SUPPORT_CODE;
+    }
+    else if (contextVk->getFeatures().emulateTransformFeedback.enabled)
     {
         compileOptions |= SH_ADD_VULKAN_XFB_EMULATION_SUPPORT_CODE;
     }