Use index fragment shader output when dual source blend is enabled (#4404)

* Use index fragment shader output when dual source blend is enabled

* Shader cache version bump

* Actually set DualSourceBlendEnabled to true

* Fix XML doc

---------

Co-authored-by: Ac_K <Acoustik666@gmail.com>

3 files changed, 53 insertions, 1 deletions

diff --git a/Ryujinx.Graphics.Shader/CodeGen/Glsl/Declarations.cs b/Ryujinx.Graphics.Shader/CodeGen/Glsl/Declarations.cs
index 996d312b..9032ca59 100644
--- a/Ryujinx.Graphics.Shader/CodeGen/Glsl/Declarations.cs
+++ b/Ryujinx.Graphics.Shader/CodeGen/Glsl/Declarations.cs
@@ -612,6 +612,19 @@ namespace Ryujinx.Graphics.Shader.CodeGen.Glsl
             else
             {
                 int usedAttributes = context.Config.UsedOutputAttributes;
+
+                if (context.Config.Stage == ShaderStage.Fragment && context.Config.GpuAccessor.QueryDualSourceBlendEnable())
+                {
+                    int firstOutput = BitOperations.TrailingZeroCount(usedAttributes);
+                    int mask = 3 << firstOutput;
+
+                    if ((usedAttributes & mask) == mask)
+                    {
+                        usedAttributes &= ~mask;
+                        DeclareOutputDualSourceBlendAttribute(context, firstOutput);
+                    }
+                }
+
                 while (usedAttributes != 0)
                 {
                     int index = BitOperations.TrailingZeroCount(usedAttributes);
@@ -690,6 +703,15 @@ namespace Ryujinx.Graphics.Shader.CodeGen.Glsl
             }
         }
 
+        private static void DeclareOutputDualSourceBlendAttribute(CodeGenContext context, int attr)
+        {
+            string name = $"{DefaultNames.OAttributePrefix}{attr}";
+            string name2 = $"{DefaultNames.OAttributePrefix}{(attr + 1)}";
+
+            context.AppendLine($"layout (location = {attr}, index = 0) out vec4 {name};");
+            context.AppendLine($"layout (location = {attr}, index = 1) out vec4 {name2};");
+        }
+
         private static void DeclareUsedOutputAttributesPerPatch(CodeGenContext context, HashSet<int> attrs)
         {
             foreach (int attr in attrs.Order())
diff --git a/Ryujinx.Graphics.Shader/CodeGen/Spirv/Declarations.cs b/Ryujinx.Graphics.Shader/CodeGen/Spirv/Declarations.cs
index 5108d861..df42a13c 100644
--- a/Ryujinx.Graphics.Shader/CodeGen/Spirv/Declarations.cs
+++ b/Ryujinx.Graphics.Shader/CodeGen/Spirv/Declarations.cs
@@ -6,6 +6,7 @@ using System;
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Linq;
+using System.Numerics;
 using static Spv.Specification;
 
 namespace Ryujinx.Graphics.Shader.CodeGen.Spirv
@@ -622,7 +623,27 @@ namespace Ryujinx.Graphics.Shader.CodeGen.Spirv
             else if (attr >= AttributeConsts.FragmentOutputColorBase && attr < AttributeConsts.FragmentOutputColorEnd)
             {
                 int location = (attr - AttributeConsts.FragmentOutputColorBase) / 16;
-                context.Decorate(spvVar, Decoration.Location, (LiteralInteger)location);
+
+                if (context.Config.Stage == ShaderStage.Fragment && context.Config.GpuAccessor.QueryDualSourceBlendEnable())
+                {
+                    int firstLocation = BitOperations.TrailingZeroCount(context.Config.UsedOutputAttributes);
+                    int index = location - firstLocation;
+                    int mask = 3 << firstLocation;
+
+                    if ((uint)index < 2 && (context.Config.UsedOutputAttributes & mask) == mask)
+                    {
+                        context.Decorate(spvVar, Decoration.Location, (LiteralInteger)firstLocation);
+                        context.Decorate(spvVar, Decoration.Index, (LiteralInteger)index);
+                    }
+                    else
+                    {
+                        context.Decorate(spvVar, Decoration.Location, (LiteralInteger)location);
+                    }
+                }
+                else
+                {
+                    context.Decorate(spvVar, Decoration.Location, (LiteralInteger)location);
+                }
             }
 
             if (!isOutAttr)
diff --git a/Ryujinx.Graphics.Shader/IGpuAccessor.cs b/Ryujinx.Graphics.Shader/IGpuAccessor.cs
index f364437c..ba5f2a92 100644
--- a/Ryujinx.Graphics.Shader/IGpuAccessor.cs
+++ b/Ryujinx.Graphics.Shader/IGpuAccessor.cs
@@ -206,6 +206,15 @@ namespace Ryujinx.Graphics.Shader
         }
 
         /// <summary>
+        /// Queries dual source blend state.
+        /// </summary>
+        /// <returns>True if blending is enabled with a dual source blend equation, false otherwise</returns>
+        bool QueryDualSourceBlendEnable()
+        {
+            return false;
+        }
+
+        /// <summary>
         /// Queries host about the presence of the FrontFacing built-in variable bug.
         /// </summary>
         /// <returns>True if the bug is present on the host device used, false otherwise</returns>