fix: Fixed reverse chunk indexing algorithm

world/chunk_data.go

@@ -16,10 +16,13 @@ func (cd *ChunkData) SectionFor(pos BlockPos) *ChunkSection {
 }
 
 func (cd *ChunkData) IndexToBlockPos(index int) BlockPos {
+	posX := index % 16
+	posZ := ((index - posX) % 256) / 16
+	posY := ((index - posZ) % 4096) / 256
 	return BlockPos{
-		X: index%16 + cd.Pos.X,
-		Y: uint(index % sliceSize),
-		Z: index%32 + cd.Pos.Z,
+		X: posX + cd.Pos.X,
+		Y: uint(posY),
+		Z: posZ + cd.Pos.Z,
 	}
 }
 

world/data_format.go

@@ -16,6 +16,10 @@ type BlockPos struct {
 	Z int  `json:"z"`
 }
 
+func (b BlockPos) String() string {
+	return fmt.Sprintf("BlockPos { X: %v, Y: %v, Z: %v }", b.X, b.Y, b.Z)
+}
+
 func RandomBlockPosWithRange(maxRange float64) BlockPos {
 	return BlockPos{
 		X: int(rand.NormFloat64() * maxRange),
@@ -54,7 +58,7 @@ func rem_euclid(a, b int) int {
 	return (a%b + b) % b
 }
 
-func (cs *ChunkSection) IndexOfBlock(pos BlockPos) int {
+func IndexOfBlock(pos BlockPos) int {
 	baseX := rem_euclid(pos.X, 16)
 	baseY := rem_euclid(int(pos.Y), 16)
 	baseZ := rem_euclid(pos.Z, 16)
@@ -69,11 +73,11 @@ func (cs *ChunkSection) UpdateBlockAtIndex(index int, targetState BlockID) {
 }
 
 func (cs *ChunkSection) UpdateBlock(pos BlockPos, targetState BlockID) {
-	cs.BlockStates[cs.IndexOfBlock(pos)] = targetState
+	cs.BlockStates[IndexOfBlock(pos)] = targetState
 }
 
 func (cs *ChunkSection) FetchBlock(pos BlockPos) BlockID {
-	return cs.BlockStates[cs.IndexOfBlock(pos)]
+	return cs.BlockStates[IndexOfBlock(pos)]
 }
 
 type BlockID uint8

world/indexing_test.go

@@ -0,0 +1,56 @@
+package world
+
+import (
+	"testing"
+)
+
+func TestUniqueDataPoints(t *testing.T) {
+	points := make(map[int]bool)
+
+	for x := 0; x < 16; x++ {
+		for y := 0; y < 16; y++ {
+			for z := 0; z < 16; z++ {
+
+				pos := BlockPos{
+					X: x,
+					Y: uint(y),
+					Z: z,
+				}
+
+				points[IndexOfBlock(pos)] = true
+			}
+		}
+	}
+
+	if len(points) != 4096 {
+		t.Fatalf("Expected %d unique points, got %d", 4096, len(points))
+	}
+}
+
+func TestCorrectIndexReversal(t *testing.T) {
+	points := make(map[int]BlockPos)
+
+	for x := 0; x < 16; x++ {
+		for y := 0; y < 16; y++ {
+			for z := 0; z < 16; z++ {
+
+				pos := BlockPos{
+					X: x,
+					Y: uint(y),
+					Z: z,
+				}
+
+				points[IndexOfBlock(pos)] = pos
+			}
+		}
+	}
+
+	var chunk ChunkData
+
+	for index, blockPos := range points {
+		testBlock := chunk.IndexToBlockPos(index)
+		if testBlock != blockPos {
+			t.Fatalf("Expected block %v, got %v", blockPos, testBlock)
+		}
+	}
+}