7 files changed, 165 insertions, 1 deletions

diff --git a/src/shader_recompiler/CMakeLists.txt b/src/shader_recompiler/CMakeLists.txt
index 545d69c7e..8cd584154 100644
--- a/src/shader_recompiler/CMakeLists.txt
+++ b/src/shader_recompiler/CMakeLists.txt
@@ -221,6 +221,7 @@ add_library(shader_recompiler STATIC
     ir_opt/dual_vertex_pass.cpp
     ir_opt/global_memory_to_storage_buffer_pass.cpp
     ir_opt/identity_removal_pass.cpp
+    ir_opt/layer_pass.cpp
     ir_opt/lower_fp16_to_fp32.cpp
     ir_opt/lower_int64_to_int32.cpp
     ir_opt/passes.h
diff --git a/src/shader_recompiler/frontend/maxwell/translate_program.cpp b/src/shader_recompiler/frontend/maxwell/translate_program.cpp
index 376aae0ea..3adbd2b16 100644
--- a/src/shader_recompiler/frontend/maxwell/translate_program.cpp
+++ b/src/shader_recompiler/frontend/maxwell/translate_program.cpp
@@ -9,6 +9,7 @@
 #include "common/settings.h"
 #include "shader_recompiler/exception.h"
 #include "shader_recompiler/frontend/ir/basic_block.h"
+#include "shader_recompiler/frontend/ir/ir_emitter.h"
 #include "shader_recompiler/frontend/ir/post_order.h"
 #include "shader_recompiler/frontend/maxwell/structured_control_flow.h"
 #include "shader_recompiler/frontend/maxwell/translate/translate.h"
@@ -233,6 +234,8 @@ IR::Program TranslateProgram(ObjectPool<IR::Inst>& inst_pool, ObjectPool<IR::Blo
         Optimization::VerificationPass(program);
     }
     Optimization::CollectShaderInfoPass(env, program);
+    Optimization::LayerPass(program, host_info);
+
     CollectInterpolationInfo(env, program);
     AddNVNStorageBuffers(program);
     return program;
@@ -331,4 +334,82 @@ void ConvertLegacyToGeneric(IR::Program& program, const Shader::RuntimeInfo& run
     }
 }
 
+IR::Program GenerateGeometryPassthrough(ObjectPool<IR::Inst>& inst_pool,
+                                        ObjectPool<IR::Block>& block_pool,
+                                        const HostTranslateInfo& host_info,
+                                        IR::Program& source_program,
+                                        Shader::OutputTopology output_topology) {
+    IR::Program program;
+    program.stage = Stage::Geometry;
+    program.output_topology = output_topology;
+    switch (output_topology) {
+    case OutputTopology::PointList:
+        program.output_vertices = 1;
+        break;
+    case OutputTopology::LineStrip:
+        program.output_vertices = 2;
+        break;
+    default:
+        program.output_vertices = 3;
+        break;
+    }
+
+    program.is_geometry_passthrough = false;
+    program.info.loads.mask = source_program.info.stores.mask;
+    program.info.stores.mask = source_program.info.stores.mask;
+    program.info.stores.Set(IR::Attribute::Layer, true);
+    program.info.stores.Set(source_program.info.emulated_layer, false);
+
+    IR::Block* current_block = block_pool.Create(inst_pool);
+    auto& node{program.syntax_list.emplace_back()};
+    node.type = IR::AbstractSyntaxNode::Type::Block;
+    node.data.block = current_block;
+
+    IR::IREmitter ir{*current_block};
+    for (u32 i = 0; i < program.output_vertices; i++) {
+        // Assign generics from input
+        for (u32 j = 0; j < 32; j++) {
+            if (!program.info.stores.Generic(j)) {
+                continue;
+            }
+
+            const IR::Attribute attr = IR::Attribute::Generic0X + (j * 4);
+            ir.SetAttribute(attr + 0, ir.GetAttribute(attr + 0, ir.Imm32(i)), ir.Imm32(0));
+            ir.SetAttribute(attr + 1, ir.GetAttribute(attr + 1, ir.Imm32(i)), ir.Imm32(0));
+            ir.SetAttribute(attr + 2, ir.GetAttribute(attr + 2, ir.Imm32(i)), ir.Imm32(0));
+            ir.SetAttribute(attr + 3, ir.GetAttribute(attr + 3, ir.Imm32(i)), ir.Imm32(0));
+        }
+
+        // Assign position from input
+        const IR::Attribute attr = IR::Attribute::PositionX;
+        ir.SetAttribute(attr + 0, ir.GetAttribute(attr + 0, ir.Imm32(i)), ir.Imm32(0));
+        ir.SetAttribute(attr + 1, ir.GetAttribute(attr + 1, ir.Imm32(i)), ir.Imm32(0));
+        ir.SetAttribute(attr + 2, ir.GetAttribute(attr + 2, ir.Imm32(i)), ir.Imm32(0));
+        ir.SetAttribute(attr + 3, ir.GetAttribute(attr + 3, ir.Imm32(i)), ir.Imm32(0));
+
+        // Assign layer
+        ir.SetAttribute(IR::Attribute::Layer, ir.GetAttribute(source_program.info.emulated_layer),
+                        ir.Imm32(0));
+
+        // Emit vertex
+        ir.EmitVertex(ir.Imm32(0));
+    }
+    ir.EndPrimitive(ir.Imm32(0));
+
+    IR::Block* return_block{block_pool.Create(inst_pool)};
+    IR::IREmitter{*return_block}.Epilogue();
+    current_block->AddBranch(return_block);
+
+    auto& merge{program.syntax_list.emplace_back()};
+    merge.type = IR::AbstractSyntaxNode::Type::Block;
+    merge.data.block = return_block;
+    program.syntax_list.emplace_back().type = IR::AbstractSyntaxNode::Type::Return;
+
+    program.blocks = GenerateBlocks(program.syntax_list);
+    program.post_order_blocks = PostOrder(program.syntax_list.front());
+    Optimization::SsaRewritePass(program);
+
+    return program;
+}
+
 } // namespace Shader::Maxwell
diff --git a/src/shader_recompiler/frontend/maxwell/translate_program.h b/src/shader_recompiler/frontend/maxwell/translate_program.h
index 02ede8c9c..497afe7cb 100644
--- a/src/shader_recompiler/frontend/maxwell/translate_program.h
+++ b/src/shader_recompiler/frontend/maxwell/translate_program.h
@@ -25,4 +25,13 @@ namespace Shader::Maxwell {
 
 void ConvertLegacyToGeneric(IR::Program& program, const RuntimeInfo& runtime_info);
 
+// Maxwell v1 and older Nvidia cards don't support setting gl_Layer from non-geometry stages.
+// This creates a workaround by setting the layer as a generic output and creating a
+// passthrough geometry shader that reads the generic and sets the layer.
+[[nodiscard]] IR::Program GenerateGeometryPassthrough(ObjectPool<IR::Inst>& inst_pool,
+                                                      ObjectPool<IR::Block>& block_pool,
+                                                      const HostTranslateInfo& host_info,
+                                                      IR::Program& source_program,
+                                                      Shader::OutputTopology output_topology);
+
 } // namespace Shader::Maxwell
diff --git a/src/shader_recompiler/host_translate_info.h b/src/shader_recompiler/host_translate_info.h
index cc1500690..d5d279554 100644
--- a/src/shader_recompiler/host_translate_info.h
+++ b/src/shader_recompiler/host_translate_info.h
@@ -13,7 +13,8 @@ struct HostTranslateInfo {
     bool support_float16{};      ///< True when the device supports 16-bit floats
     bool support_int64{};        ///< True when the device supports 64-bit integers
     bool needs_demote_reorder{}; ///< True when the device needs DemoteToHelperInvocation reordered
-    bool support_snorm_render_buffer{}; ///< True when the device supports SNORM render buffers
+    bool support_snorm_render_buffer{};  ///< True when the device supports SNORM render buffers
+    bool support_viewport_index_layer{}; ///< True when the device supports gl_Layer in VS
 };
 
 } // namespace Shader
diff --git a/src/shader_recompiler/ir_opt/layer_pass.cpp b/src/shader_recompiler/ir_opt/layer_pass.cpp
new file mode 100644
index 000000000..4574f7cf2
--- /dev/null
+++ b/src/shader_recompiler/ir_opt/layer_pass.cpp
@@ -0,0 +1,68 @@
+// SPDX-FileCopyrightText: Copyright 2022 yuzu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <algorithm>
+#include <bit>
+#include <optional>
+
+#include <boost/container/small_vector.hpp>
+
+#include "shader_recompiler/environment.h"
+#include "shader_recompiler/frontend/ir/basic_block.h"
+#include "shader_recompiler/frontend/ir/breadth_first_search.h"
+#include "shader_recompiler/frontend/ir/ir_emitter.h"
+#include "shader_recompiler/host_translate_info.h"
+#include "shader_recompiler/ir_opt/passes.h"
+#include "shader_recompiler/shader_info.h"
+
+namespace Shader::Optimization {
+
+static IR::Attribute EmulatedLayerAttribute(VaryingState& stores) {
+    for (u32 i = 0; i < 32; i++) {
+        if (!stores.Generic(i)) {
+            return IR::Attribute::Generic0X + (i * 4);
+        }
+    }
+    return IR::Attribute::Layer;
+}
+
+static bool PermittedProgramStage(Stage stage) {
+    switch (stage) {
+    case Stage::VertexA:
+    case Stage::VertexB:
+    case Stage::TessellationControl:
+    case Stage::TessellationEval:
+        return true;
+    default:
+        return false;
+    }
+}
+
+void LayerPass(IR::Program& program, const HostTranslateInfo& host_info) {
+    if (host_info.support_viewport_index_layer || !PermittedProgramStage(program.stage)) {
+        return;
+    }
+
+    const auto end{program.post_order_blocks.end()};
+    const auto layer_attribute = EmulatedLayerAttribute(program.info.stores);
+    bool requires_layer_emulation = false;
+
+    for (auto block = program.post_order_blocks.begin(); block != end; ++block) {
+        for (IR::Inst& inst : (*block)->Instructions()) {
+            if (inst.GetOpcode() == IR::Opcode::SetAttribute &&
+                inst.Arg(0).Attribute() == IR::Attribute::Layer) {
+                requires_layer_emulation = true;
+                inst.SetArg(0, IR::Value{layer_attribute});
+            }
+        }
+    }
+
+    if (requires_layer_emulation) {
+        program.info.requires_layer_emulation = true;
+        program.info.emulated_layer = layer_attribute;
+        program.info.stores.Set(IR::Attribute::Layer, false);
+        program.info.stores.Set(layer_attribute, true);
+    }
+}
+
+} // namespace Shader::Optimization
diff --git a/src/shader_recompiler/ir_opt/passes.h b/src/shader_recompiler/ir_opt/passes.h
index 586a0668f..11bfe801a 100644
--- a/src/shader_recompiler/ir_opt/passes.h
+++ b/src/shader_recompiler/ir_opt/passes.h
@@ -23,6 +23,7 @@ void RescalingPass(IR::Program& program);
 void SsaRewritePass(IR::Program& program);
 void PositionPass(Environment& env, IR::Program& program);
 void TexturePass(Environment& env, IR::Program& program, const HostTranslateInfo& host_info);
+void LayerPass(IR::Program& program, const HostTranslateInfo& host_info);
 void VerificationPass(const IR::Program& program);
 
 // Dual Vertex
diff --git a/src/shader_recompiler/shader_info.h b/src/shader_recompiler/shader_info.h
index ee6252bb5..d9c6e92db 100644
--- a/src/shader_recompiler/shader_info.h
+++ b/src/shader_recompiler/shader_info.h
@@ -204,6 +204,9 @@ struct Info {
     u32 nvn_buffer_base{};
     std::bitset<16> nvn_buffer_used{};
 
+    bool requires_layer_emulation{};
+    IR::Attribute emulated_layer{};
+
     boost::container::static_vector<ConstantBufferDescriptor, MAX_CBUFS>
         constant_buffer_descriptors;
     boost::container::static_vector<StorageBufferDescriptor, MAX_SSBOS> storage_buffers_descriptors;