Patch supplied by contributor to improve the texture sheet use with the UIParticlesystem

Author: SimonDarksideJ

Runtime/Scripts/Effects/UIParticleSystem.cs

@@ -223,9 +223,10 @@ protected override void OnPopulateMesh(VertexHelper vh)
                             frame = Mathf.FloorToInt(frameProgress * textureSheetAnimation.numTilesX);
 
                             int row = textureSheetAnimation.rowIndex;
-                            //                    if (textureSheetAnimation.useRandomRow) { // FIXME - is this handled internally by rowIndex?
-                            //                        row = Random.Range(0, textureSheetAnimation.numTilesY, using: particle.randomSeed);
-                            //                    }
+                            if (textureSheetAnimation.rowMode == ParticleSystemAnimationRowMode.Random)
+                            { // FIXME - is this handled internally by rowIndex?
+                                row = Mathf.Abs((int)particle.randomSeed % textureSheetAnimation.numTilesY);
+                            }
                             frame += row * textureSheetAnimation.numTilesX;
                             break;
 
@@ -234,7 +235,7 @@ protected override void OnPopulateMesh(VertexHelper vh)
                     frame %= textureSheetAnimationFrames;
 
                     particleUV.x = (frame % textureSheetAnimation.numTilesX) * textureSheetAnimationFrameSize.x;
-                    particleUV.y = 1.0f - Mathf.FloorToInt(frame / textureSheetAnimation.numTilesX) * textureSheetAnimationFrameSize.y;
+                    particleUV.y = 1.0f - ((frame / textureSheetAnimation.numTilesX) + 1) * textureSheetAnimationFrameSize.y;
                     particleUV.z = particleUV.x + textureSheetAnimationFrameSize.x;
                     particleUV.w = particleUV.y + textureSheetAnimationFrameSize.y;
                 }