3 files changed, 61 insertions, 1 deletions
diff --git a/Ryujinx.Graphics.Shader/CodeGen/Glsl/Instructions/InstGenMemory.cs b/Ryujinx.Graphics.Shader/CodeGen/Glsl/Instructions/InstGenMemory.cs
index 263eada6..a5d2632c 100644
--- a/Ryujinx.Graphics.Shader/CodeGen/Glsl/Instructions/InstGenMemory.cs
+++ b/Ryujinx.Graphics.Shader/CodeGen/Glsl/Instructions/InstGenMemory.cs
@@ -677,7 +677,28 @@ namespace Ryujinx.Graphics.Shader.CodeGen.Glsl.Instructions
                 return vector;
             }
 
-            Append(ApplyScaling(AssemblePVector(pCount)));
+            string ApplyBias(string vector)
+            {
+                int gatherBiasPrecision = context.Config.GpuAccessor.QueryHostGatherBiasPrecision();
+                if (isGather && gatherBiasPrecision != 0)
+                {
+                    // GPU requires texture gather to be slightly offset to match NVIDIA behaviour when point is exactly between two texels.
+                    // Offset by the gather precision divided by 2 to correct for rounding.
+
+                    if (pCount == 1)
+                    {
+                        vector = $"{vector} + (1.0 / (float(textureSize({samplerName}, 0)) * float({1 << (gatherBiasPrecision + 1)})))";
+                    }
+                    else
+                    {
+                        vector = $"{vector} + (1.0 / (vec{pCount}(textureSize({samplerName}, 0).{"xyz".Substring(0, pCount)}) * float({1 << (gatherBiasPrecision + 1)})))";
+                    }
+                }
+
+                return vector;
+            }
+
+            Append(ApplyBias(ApplyScaling(AssemblePVector(pCount))));
 
             string AssembleDerivativesVector(int count)
             {
diff --git a/Ryujinx.Graphics.Shader/CodeGen/Spirv/Instructions.cs b/Ryujinx.Graphics.Shader/CodeGen/Spirv/Instructions.cs
index 14d6ab52..b3db1905 100644
--- a/Ryujinx.Graphics.Shader/CodeGen/Spirv/Instructions.cs
+++ b/Ryujinx.Graphics.Shader/CodeGen/Spirv/Instructions.cs
@@ -4,6 +4,7 @@ using Ryujinx.Graphics.Shader.Translation;
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Linq;
 using System.Numerics;
 using static Spv.Specification;
 
@@ -1556,6 +1557,33 @@ namespace Ryujinx.Graphics.Shader.CodeGen.Spirv
                 }
             }
 
+            SpvInstruction ApplyBias(SpvInstruction vector, SpvInstruction image)
+            {
+                int gatherBiasPrecision = context.Config.GpuAccessor.QueryHostGatherBiasPrecision();
+                if (isGather && gatherBiasPrecision != 0)
+                {
+                    // GPU requires texture gather to be slightly offset to match NVIDIA behaviour when point is exactly between two texels.
+                    // Offset by the gather precision divided by 2 to correct for rounding.
+                    var sizeType = pCount == 1 ? context.TypeS32() : context.TypeVector(context.TypeS32(), pCount);
+                    var pVectorType = pCount == 1 ? context.TypeFP32() : context.TypeVector(context.TypeFP32(), pCount);
+
+                    var bias = context.Constant(context.TypeFP32(), (float)(1 << (gatherBiasPrecision + 1)));
+                    var biasVector = context.CompositeConstruct(pVectorType, Enumerable.Repeat(bias, pCount).ToArray());
+
+                    var one = context.Constant(context.TypeFP32(), 1f);
+                    var oneVector = context.CompositeConstruct(pVectorType, Enumerable.Repeat(one, pCount).ToArray());
+
+                    var divisor = context.FMul(
+                        pVectorType,
+                        context.ConvertSToF(pVectorType, context.ImageQuerySize(sizeType, image)),
+                        biasVector);
+
+                    vector = context.FAdd(pVectorType, vector, context.FDiv(pVectorType, oneVector, divisor));
+                }
+
+                return vector;
+            }
+
             SpvInstruction pCoords = AssemblePVector(pCount);
             pCoords = ScalingHelpers.ApplyScaling(context, texOp, pCoords, intCoords, isBindless, isIndexed, isArray, pCount);
 
@@ -1716,6 +1744,8 @@ namespace Ryujinx.Graphics.Shader.CodeGen.Spirv
                 image = context.Image(imageType, image);
             }
 
+            pCoords = ApplyBias(pCoords, image);
+
             var operands = operandsList.ToArray();
 
             SpvInstruction result;
diff --git a/Ryujinx.Graphics.Shader/IGpuAccessor.cs b/Ryujinx.Graphics.Shader/IGpuAccessor.cs
index ba5f2a92..bc5e67c3 100644
--- a/Ryujinx.Graphics.Shader/IGpuAccessor.cs
+++ b/Ryujinx.Graphics.Shader/IGpuAccessor.cs
@@ -197,6 +197,15 @@ namespace Ryujinx.Graphics.Shader
         }
 
         /// <summary>
+        /// Queries host's gather operation precision bits for biasing their coordinates. Zero means no bias.
+        /// </summary>
+        /// <returns>Bits of gather operation precision to use for coordinate bias</returns>
+        int QueryHostGatherBiasPrecision()
+        {
+            return 0;
+        }
+
+        /// <summary>
         /// Queries host about whether to reduce precision to improve performance.
         /// </summary>
         /// <returns>True if precision is limited to vertex position, false otherwise</returns>