Reorient water quads according to the corner heights (CaffeineMC#2467)

The seam is placed such that it touches either the highest or lowest corner.

Closes CaffeineMC#609

src/main/java/me/jellysquid/mods/sodium/client/render/chunk/compile/pipeline/FluidRenderer.java

@@ -44,6 +44,7 @@ public class FluidRenderer {
     // TODO: allow this to be changed by vertex format
     // TODO: move fluid rendering to a separate render pass and control glPolygonOffset and glDepthFunc to fix this properly
     private static final float EPSILON = 0.001f;
+    private static final float ALIGNED_EQUALS_EPSILON = 0.011f;
 
     private final BlockPos.Mutable scratchPos = new BlockPos.Mutable();
     private final MutableFloat scratchHeight = new MutableFloat(0);
@@ -96,6 +97,10 @@ private boolean isSideExposed(BlockRenderView world, int x, int y, int z, Direct
         return true;
     }
 
+    private static boolean isAlignedEquals(float a, float b) {
+        return Math.abs(a - b) <= ALIGNED_EQUALS_EPSILON;
+    }
+
     public void render(WorldSlice world, FluidState fluidState, BlockPos blockPos, BlockPos offset, ChunkBuildBuffers buffers) {
         var material = DefaultMaterials.forFluidState(fluidState);
         var meshBuilder = buffers.get(material);
@@ -215,10 +220,30 @@ public void render(WorldSlice world, FluidState fluidState, BlockPos blockPos, B
 
             quad.setSprite(sprite);
 
-            setVertex(quad, 0, 0.0f, northWestHeight, 0.0f, u1, v1);
-            setVertex(quad, 1, 0.0f, southWestHeight, 1.0F, u2, v2);
-            setVertex(quad, 2, 1.0F, southEastHeight, 1.0F, u3, v3);
-            setVertex(quad, 3, 1.0F, northEastHeight, 0.0f, u4, v4);
+
+            // top surface alignedness is calculated with a more relaxed epsilon
+            boolean aligned = isAlignedEquals(northEastHeight, northWestHeight)
+                    && isAlignedEquals(northWestHeight, southEastHeight)
+                    && isAlignedEquals(southEastHeight, southWestHeight)
+                    && isAlignedEquals(southWestHeight, northEastHeight);
+
+            boolean creaseNorthEastSouthWest = aligned
+                    || northEastHeight > northWestHeight && northEastHeight > southEastHeight
+                    || northEastHeight < northWestHeight && northEastHeight < southEastHeight
+                    || southWestHeight > northWestHeight && southWestHeight > southEastHeight
+                    || southWestHeight < northWestHeight && southWestHeight < southEastHeight;
+
+            if (creaseNorthEastSouthWest) {
+                setVertex(quad, 1, 0.0f, northWestHeight, 0.0f, u1, v1);
+                setVertex(quad, 2, 0.0f, southWestHeight, 1.0F, u2, v2);
+                setVertex(quad, 3, 1.0F, southEastHeight, 1.0F, u3, v3);
+                setVertex(quad, 0, 1.0F, northEastHeight, 0.0f, u4, v4);
+            } else {
+                setVertex(quad, 0, 0.0f, northWestHeight, 0.0f, u1, v1);
+                setVertex(quad, 1, 0.0f, southWestHeight, 1.0F, u2, v2);
+                setVertex(quad, 2, 1.0F, southEastHeight, 1.0F, u3, v3);
+                setVertex(quad, 3, 1.0F, northEastHeight, 0.0f, u4, v4);
+            }
 
             this.updateQuad(quad, world, blockPos, lighter, Direction.UP, 1.0F, colorProvider, fluidState);
             this.writeQuad(meshBuilder, material, offset, quad, facing, false);
@@ -228,7 +253,6 @@ public void render(WorldSlice world, FluidState fluidState, BlockPos blockPos, B
                         ModelQuadFacing.NEG_Y, true);
 
             }
-
         }
 
         if (!sfDown) {
@@ -363,7 +387,7 @@ private ColorProvider<FluidState> getColorProvider(Fluid fluid, FluidRenderHandl
         if (override != null) {
             return override;
         }
-        
+
         return DefaultColorProviders.adapt(handler);
     }
 
@@ -397,7 +421,7 @@ private void writeQuad(ChunkModelBuilder builder, Material material, BlockPos of
         var vertices = this.vertices;
 
         for (int i = 0; i < 4; i++) {
-            var out = vertices[flip ? 3 - i : i];
+            var out = vertices[flip ? (3 - i + 1) & 0b11 : i];
             out.x = offset.getX() + quad.getX(i);
             out.y = offset.getY() + quad.getY(i);
             out.z = offset.getZ() + quad.getZ(i);