From 9dba7caa885dec35fdec13e2fcb100e453ff22b1 Mon Sep 17 00:00:00 2001
From: Wojtek Figat <wojtek@figat.pl>
Date: Wed, 16 Apr 2025 10:01:23 +0200
Subject: [PATCH] Another fix for flipbook to work with all cases

#3381
---
 Source/Shaders/MaterialCommon.hlsl | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/Source/Shaders/MaterialCommon.hlsl b/Source/Shaders/MaterialCommon.hlsl
index b766a307b..31d711547 100644
--- a/Source/Shaders/MaterialCommon.hlsl
+++ b/Source/Shaders/MaterialCommon.hlsl
@@ -309,10 +309,11 @@ float3 AOMultiBounce(float visibility, float3 albedo)
 
 float2 Flipbook(float2 uv, float frame, float2 sizeXY, float2 flipXY = 0.0f)
 {
-    float2 frameXY = float2((uint)frame / (uint)sizeXY.y, (uint)frame / (uint)sizeXY.x);
-    float2 flipFrameXY = sizeXY - frameXY - float2(1, 1);
-    frameXY = lerp(frameXY, flipFrameXY, flipXY);
-    return (uv + frameXY) / sizeXY;
+    uint tile = (uint)fmod(frame, sizeXY.x * sizeXY.y);
+    float2 tileCount = float2(1.0, 1.0) / sizeXY;
+    float tileY = abs(flipXY.y * sizeXY.y - (floor(tile * tileCount.x) + flipXY.y * 1));
+    float tileX = abs(flipXY.x * sizeXY.x - ((tile - sizeXY.x * floor(tile * tileCount.x)) + flipXY.x * 1));
+    return (uv + float2(tileX, tileY)) * tileCount;
 }
 
 // Calculates the world-position offset to stabilize tiling (eg. via triplanar mapping) due to Large Worlds view origin offset.