gl_shader_decompiler: Implement gl_ViewportIndex and gl_Layer in vertex shaders

This commit implements gl_ViewportIndex and gl_Layer in vertex and
geometry shaders. In the case it's used in a vertex shader, it requires
ARB_shader_viewport_layer_array. This extension is available on AMD and
Nvidia devices (mesa and proprietary drivers), but not available on
Intel on any platform. At the moment of writing this description I don't
know if this is a hardware limitation or a driver limitation.

In the case that ARB_shader_viewport_layer_array is not available,
writes to these registers on a vertex shader are ignored, with the
appropriate logging.

src/video_core/engines/shader_bytecode.h

@@ -78,7 +78,7 @@ union Attribute {
     constexpr explicit Attribute(u64 value) : value(value) {}
 
     enum class Index : u64 {
-        PointSize = 6,
+        LayerViewportPointSize = 6,
         Position = 7,
         Attribute_0 = 8,
         Attribute_31 = 39,

src/video_core/renderer_opengl/gl_device.cpp

@@ -26,6 +26,7 @@ Device::Device() {
     uniform_buffer_alignment = GetInteger<std::size_t>(GL_UNIFORM_BUFFER_OFFSET_ALIGNMENT);
     max_vertex_attributes = GetInteger<u32>(GL_MAX_VERTEX_ATTRIBS);
     max_varyings = GetInteger<u32>(GL_MAX_VARYING_VECTORS);
+    has_vertex_viewport_layer = GLAD_GL_ARB_shader_viewport_layer_array;
     has_variable_aoffi = TestVariableAoffi();
     has_component_indexing_bug = TestComponentIndexingBug();
 }
@@ -34,6 +35,7 @@ Device::Device(std::nullptr_t) {
     uniform_buffer_alignment = 0;
     max_vertex_attributes = 16;
     max_varyings = 15;
+    has_vertex_viewport_layer = true;
     has_variable_aoffi = true;
     has_component_indexing_bug = false;
 }

src/video_core/renderer_opengl/gl_device.h

@@ -26,6 +26,10 @@ public:
         return max_varyings;
     }
 
+    bool HasVertexViewportLayer() const {
+        return has_vertex_viewport_layer;
+    }
+
     bool HasVariableAoffi() const {
         return has_variable_aoffi;
     }
@@ -41,6 +45,7 @@ private:
     std::size_t uniform_buffer_alignment{};
     u32 max_vertex_attributes{};
     u32 max_varyings{};
+    bool has_vertex_viewport_layer{};
     bool has_variable_aoffi{};
     bool has_component_indexing_bug{};
 };

src/video_core/renderer_opengl/gl_shader_cache.cpp

@@ -182,8 +182,11 @@ CachedProgram SpecializeShader(const std::string& code, const GLShader::ShaderEn
     const auto texture_buffer_usage{variant.texture_buffer_usage};
 
     std::string source = "#version 430 core\n"
-                         "#extension GL_ARB_separate_shader_objects : enable\n\n";
+                         "#extension GL_ARB_separate_shader_objects : enable\n";
-    source += fmt::format("#define EMULATION_UBO_BINDING {}\n", base_bindings.cbuf++);
+    if (entries.shader_viewport_layer_array) {
+        source += "#extension GL_ARB_shader_viewport_layer_array : enable\n";
+    }
+    source += fmt::format("\n#define EMULATION_UBO_BINDING {}\n", base_bindings.cbuf++);
 
     for (const auto& cbuf : entries.const_buffers) {
         source +=

src/video_core/renderer_opengl/gl_shader_decompiler.cpp

@@ -14,6 +14,7 @@
 #include "common/alignment.h"
 #include "common/assert.h"
 #include "common/common_types.h"
+#include "common/logging/log.h"
 #include "video_core/engines/maxwell_3d.h"
 #include "video_core/renderer_opengl/gl_device.h"
 #include "video_core/renderer_opengl/gl_rasterizer.h"
@@ -244,6 +245,8 @@ public:
                                                        usage.is_read, usage.is_written);
         }
         entries.clip_distances = ir.GetClipDistances();
+        entries.shader_viewport_layer_array =
+            stage == ShaderStage::Vertex && (ir.UsesLayer() || ir.UsesPointSize());
         entries.shader_length = ir.GetLength();
         return entries;
     }
@@ -280,22 +283,34 @@ private:
     }
 
     void DeclareVertexRedeclarations() {
-        bool clip_distances_declared = false;
-
         code.AddLine("out gl_PerVertex {{");
         ++code.scope;
 
         code.AddLine("vec4 gl_Position;");
 
-        for (const auto o : ir.GetOutputAttributes()) {
+        for (const auto attribute : ir.GetOutputAttributes()) {
-            if (o == Attribute::Index::PointSize)
+            if (attribute == Attribute::Index::ClipDistances0123 ||
-                code.AddLine("float gl_PointSize;");
+                attribute == Attribute::Index::ClipDistances4567) {
-            if (!clip_distances_declared && (o == Attribute::Index::ClipDistances0123 ||
-                                             o == Attribute::Index::ClipDistances4567)) {
                 code.AddLine("float gl_ClipDistance[];");
-                clip_distances_declared = true;
+                break;
             }
         }
+        if (stage != ShaderStage::Vertex || device.HasVertexViewportLayer()) {
+            if (ir.UsesLayer()) {
+                code.AddLine("int gl_Layer;");
+            }
+            if (ir.UsesViewportIndex()) {
+                code.AddLine("int gl_ViewportIndex;");
+            }
+        } else if (stage == ShaderStage::Vertex && !device.HasVertexViewportLayer()) {
+            LOG_ERROR(
+                Render_OpenGL,
+                "GL_ARB_shader_viewport_layer_array is not available and its required by a shader");
+        }
+
+        if (ir.UsesPointSize()) {
+            code.AddLine("int gl_PointSize;");
+        }
 
         --code.scope;
         code.AddLine("}};");
@@ -803,6 +818,45 @@ private:
         return CastOperand(VisitOperand(operation, operand_index), type);
     }
 
+    std::optional<std::pair<std::string, bool>> GetOutputAttribute(const AbufNode* abuf) {
+        switch (const auto attribute = abuf->GetIndex()) {
+        case Attribute::Index::Position:
+            return std::make_pair("gl_Position"s + GetSwizzle(abuf->GetElement()), false);
+        case Attribute::Index::LayerViewportPointSize:
+            switch (abuf->GetElement()) {
+            case 0:
+                UNIMPLEMENTED();
+                return {};
+            case 1:
+                if (stage == ShaderStage::Vertex && !device.HasVertexViewportLayer()) {
+                    return {};
+                }
+                return std::make_pair("gl_Layer", true);
+            case 2:
+                if (stage == ShaderStage::Vertex && !device.HasVertexViewportLayer()) {
+                    return {};
+                }
+                return std::make_pair("gl_ViewportIndex", true);
+            case 3:
+                UNIMPLEMENTED_MSG("Requires some state changes for gl_PointSize to work in shader");
+                return std::make_pair("gl_PointSize", false);
+            }
+            return {};
+        case Attribute::Index::ClipDistances0123:
+            return std::make_pair(fmt::format("gl_ClipDistance[{}]", abuf->GetElement()), false);
+        case Attribute::Index::ClipDistances4567:
+            return std::make_pair(fmt::format("gl_ClipDistance[{}]", abuf->GetElement() + 4),
+                                  false);
+        default:
+            if (IsGenericAttribute(attribute)) {
+                return std::make_pair(
+                    GetOutputAttribute(attribute) + GetSwizzle(abuf->GetElement()), false);
+            }
+            UNIMPLEMENTED_MSG("Unhandled output attribute: {}", static_cast<u32>(attribute));
+            return {};
+        }
+    }
+
     std::string CastOperand(const std::string& value, Type type) const {
         switch (type) {
         case Type::Bool:
@@ -999,6 +1053,8 @@ private:
         const Node& src = operation[1];
 
         std::string target;
+        bool is_integer = false;
+
         if (const auto gpr = std::get_if<GprNode>(&*dest)) {
             if (gpr->GetIndex() == Register::ZeroIndex) {
                 // Writing to Register::ZeroIndex is a no op
@@ -1007,26 +1063,12 @@ private:
             target = GetRegister(gpr->GetIndex());
         } else if (const auto abuf = std::get_if<AbufNode>(&*dest)) {
             UNIMPLEMENTED_IF(abuf->IsPhysicalBuffer());
-
+            const auto result = GetOutputAttribute(abuf);
-            target = [&]() -> std::string {
+            if (!result) {
-                switch (const auto attribute = abuf->GetIndex(); abuf->GetIndex()) {
+                return {};
-                case Attribute::Index::Position:
-                    return "gl_Position"s + GetSwizzle(abuf->GetElement());
-                case Attribute::Index::PointSize:
-                    return "gl_PointSize";
-                case Attribute::Index::ClipDistances0123:
-                    return fmt::format("gl_ClipDistance[{}]", abuf->GetElement());
-                case Attribute::Index::ClipDistances4567:
-                    return fmt::format("gl_ClipDistance[{}]", abuf->GetElement() + 4);
-                default:
-                    if (IsGenericAttribute(attribute)) {
-                        return GetOutputAttribute(attribute) + GetSwizzle(abuf->GetElement());
             }
-                    UNIMPLEMENTED_MSG("Unhandled output attribute: {}",
+            target = result->first;
-                                      static_cast<u32>(attribute));
+            is_integer = result->second;
-                    return "0";
-                }
-            }();
         } else if (const auto lmem = std::get_if<LmemNode>(&*dest)) {
             target = fmt::format("{}[ftou({}) / 4]", GetLocalMemory(), Visit(lmem->GetAddress()));
         } else if (const auto gmem = std::get_if<GmemNode>(&*dest)) {
@@ -1038,7 +1080,11 @@ private:
             UNREACHABLE_MSG("Assign called without a proper target");
         }
 
+        if (is_integer) {
+            code.AddLine("{} = ftoi({});", target, Visit(src));
+        } else {
             code.AddLine("{} = {};", target, Visit(src));
+        }
         return {};
     }
 

src/video_core/renderer_opengl/gl_shader_decompiler.h

@@ -78,6 +78,7 @@ struct ShaderEntries {
     std::vector<ImageEntry> images;
     std::vector<GlobalMemoryEntry> global_memory_entries;
     std::array<bool, Maxwell::NumClipDistances> clip_distances{};
+    bool shader_viewport_layer_array{};
     std::size_t shader_length{};
 };
 

src/video_core/renderer_opengl/gl_shader_disk_cache.cpp

@@ -373,6 +373,12 @@ std::optional<ShaderDiskCacheDecompiled> ShaderDiskCacheOpenGL::LoadDecompiledEn
         }
     }
 
+    bool shader_viewport_layer_array{};
+    if (!LoadObjectFromPrecompiled(shader_viewport_layer_array)) {
+        return {};
+    }
+    entry.entries.shader_viewport_layer_array = shader_viewport_layer_array;
+
     u64 shader_length{};
     if (!LoadObjectFromPrecompiled(shader_length)) {
         return {};
@@ -445,6 +451,10 @@ bool ShaderDiskCacheOpenGL::SaveDecompiledFile(u64 unique_identifier, const std:
         }
     }
 
+    if (!SaveObjectToPrecompiled(entries.shader_viewport_layer_array)) {
+        return false;
+    }
+
     if (!SaveObjectToPrecompiled(static_cast<u64>(entries.shader_length))) {
         return false;
     }

src/video_core/renderer_vulkan/vk_shader_decompiler.cpp

@@ -430,12 +430,9 @@ private:
         instance_index = DeclareBuiltIn(spv::BuiltIn::InstanceIndex, spv::StorageClass::Input,
                                         t_in_uint, "instance_index");
 
-        bool is_point_size_declared = false;
         bool is_clip_distances_declared = false;
         for (const auto index : ir.GetOutputAttributes()) {
-            if (index == Attribute::Index::PointSize) {
+            if (index == Attribute::Index::ClipDistances0123 ||
-                is_point_size_declared = true;
-            } else if (index == Attribute::Index::ClipDistances0123 ||
                 index == Attribute::Index::ClipDistances4567) {
                 is_clip_distances_declared = true;
             }
@@ -443,7 +440,7 @@ private:
 
         std::vector<Id> members;
         members.push_back(t_float4);
-        if (is_point_size_declared) {
+        if (ir.UsesPointSize()) {
             members.push_back(t_float);
         }
         if (is_clip_distances_declared) {
@@ -466,7 +463,7 @@ private:
 
         position_index = MemberDecorateBuiltIn(spv::BuiltIn::Position, "position", true);
         point_size_index =
-            MemberDecorateBuiltIn(spv::BuiltIn::PointSize, "point_size", is_point_size_declared);
+            MemberDecorateBuiltIn(spv::BuiltIn::PointSize, "point_size", ir.UsesPointSize());
         clip_distances_index = MemberDecorateBuiltIn(spv::BuiltIn::ClipDistance, "clip_distances",
                                                      is_clip_distances_declared);
 
@@ -712,7 +709,8 @@ private:
                 case Attribute::Index::Position:
                     return AccessElement(t_out_float, per_vertex, position_index,
                                          abuf->GetElement());
-                case Attribute::Index::PointSize:
+                case Attribute::Index::LayerViewportPointSize:
+                    UNIMPLEMENTED_IF(abuf->GetElement() != 3);
                     return AccessElement(t_out_float, per_vertex, point_size_index);
                 case Attribute::Index::ClipDistances0123:
                     return AccessElement(t_out_float, per_vertex, clip_distances_index,

src/video_core/shader/shader_ir.cpp

@@ -89,6 +89,22 @@ Node ShaderIR::GetPhysicalInputAttribute(Tegra::Shader::Register physical_addres
 }
 
 Node ShaderIR::GetOutputAttribute(Attribute::Index index, u64 element, Node buffer) {
+    if (index == Attribute::Index::LayerViewportPointSize) {
+        switch (element) {
+        case 0:
+            UNIMPLEMENTED();
+            break;
+        case 1:
+            uses_layer = true;
+            break;
+        case 2:
+            uses_viewport_index = true;
+            break;
+        case 3:
+            uses_point_size = true;
+            break;
+        }
+    }
     if (index == Attribute::Index::ClipDistances0123 ||
         index == Attribute::Index::ClipDistances4567) {
         const auto clip_index =

src/video_core/shader/shader_ir.h

@@ -121,6 +121,18 @@ public:
         return static_cast<std::size_t>(coverage_end * sizeof(u64));
     }
 
+    bool UsesLayer() const {
+        return uses_layer;
+    }
+
+    bool UsesViewportIndex() const {
+        return uses_viewport_index;
+    }
+
+    bool UsesPointSize() const {
+        return uses_point_size;
+    }
+
     bool HasPhysicalAttributes() const {
         return uses_physical_attributes;
     }
@@ -343,6 +355,9 @@ private:
     std::set<Image> used_images;
     std::array<bool, Tegra::Engines::Maxwell3D::Regs::NumClipDistances> used_clip_distances{};
     std::map<GlobalMemoryBase, GlobalMemoryUsage> used_global_memory;
+    bool uses_layer{};
+    bool uses_viewport_index{};
+    bool uses_point_size{};
     bool uses_physical_attributes{}; // Shader uses AL2P or physical attribute read/writes
 
     Tegra::Shader::Header header;