From 12356d7342c1ed120cf4ed788f7f8239843aa174 Mon Sep 17 00:00:00 2001
From: Joshua Ashton <joshua@froggi.es>
Date: Mon, 1 Jun 2020 13:32:54 +0100
Subject: [PATCH] [dxso] Bias FETCH4 half-texel offset to avoid grid effect

---
 src/dxso/dxso_compiler.cpp | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/dxso/dxso_compiler.cpp b/src/dxso/dxso_compiler.cpp
index a7f20ccb578..92d0d7d3d3c 100644
--- a/src/dxso/dxso_compiler.cpp
+++ b/src/dxso/dxso_compiler.cpp
@@ -3110,7 +3110,12 @@ void DxsoCompiler::emitControlFlowGenericLoop(
 
         textureSize.type = { DxsoScalarType::Float32, samplerInfo.dimensions };
         textureSize.id = m_module.opConvertStoF(getVectorTypeId(textureSize.type), textureSize.id);
-        textureSize.id = m_module.opFDiv(getVectorTypeId(textureSize.type), m_module.constfReplicant(1.0f, samplerInfo.dimensions), textureSize.id);
+        // HACK: Bias fetch4 half-texel offset to avoid a "grid" effect.
+        // Technically we should only do that for non-powers of two
+        // as only then does the imprecision need to be biased
+        // towards infinity -- but that's not really worth doing...
+        float numerator = 1.0f - 1.0f / 256.0f;
+        textureSize.id = m_module.opFDiv(getVectorTypeId(textureSize.type), m_module.constfReplicant(numerator, samplerInfo.dimensions), textureSize.id);
 
         // coord => same dimensions as texture size (no cube here !)
         const std::array<uint32_t, 4> naturalIndices = { 0, 1, 2, 3 };