Swizzle

- Switch to Y X Z ordering
- In theory this will be more coherent since the first lut step on the
  GPU will have a more constrained range of values in the worst case

common/src/backend/java/dev/engine_room/flywheel/backend/engine/LightLut.java

@@ -9,6 +9,7 @@
 import net.minecraft.core.SectionPos;
 
 // Massive kudos to RogueLogix for figuring out this LUT scheme.
+// First layer is Y, then X, then Z.
 public final class LightLut {
 	private final Layer<Layer<IntLayer>> indices = new Layer<>();
 
@@ -17,8 +18,8 @@ public void add(long position, int index) {
 		final var y = SectionPos.y(position);
 		final var z = SectionPos.z(position);
 
-		indices.computeIfAbsent(x, Layer::new)
-				.computeIfAbsent(y, IntLayer::new)
+		indices.computeIfAbsent(y, Layer::new)
+				.computeIfAbsent(x, IntLayer::new)
 				.set(z, index + 1);
 	}
 
@@ -27,13 +28,13 @@ public void remove(long section) {
 		final var y = SectionPos.y(section);
 		final var z = SectionPos.z(section);
 
-		var first = indices.get(x);
+		var first = indices.get(y);
 
 		if (first == null) {
 			return;
 		}
 
-		var second = first.get(y);
+		var second = first.get(x);
 
 		if (second == null) {
 			return;

common/src/backend/resources/assets/flywheel/flywheel/internal/light_lut.glsl

@@ -43,18 +43,18 @@ bool _flw_nextLut(uint base, int coord, out uint next) {
 }
 
 bool _flw_chunkCoordToSectionIndex(ivec3 sectionPos, out uint index) {
-    uint y;
-    if (_flw_nextLut(0, sectionPos.x, y) || y == 0) {
+    uint first;
+    if (_flw_nextLut(0, sectionPos.y, first) || first == 0) {
         return true;
     }
 
-    uint z;
-    if (_flw_nextLut(y, sectionPos.y, z) || z == 0) {
+    uint second;
+    if (_flw_nextLut(first, sectionPos.x, second) || second == 0) {
         return true;
     }
 
     uint sectionIndex;
-    if (_flw_nextLut(z, sectionPos.z, sectionIndex) || sectionIndex == 0) {
+    if (_flw_nextLut(second, sectionPos.z, sectionIndex) || sectionIndex == 0) {
         return true;
     }