Mark out-of-bound blocks as UNDEFINED

world.js

@@ -1,6 +1,7 @@
 import { makeBufferFromFaces, makeFace} from "./geometry";
 
 export const BlockType = {
+    UNDEFINED: 0,
     AIR: 1,
     DIRT: 2,
     GRASS: 3,
@@ -87,6 +88,11 @@ function makeChunk(z, x) {
 }
 
 export function blockLookup(world, x, y, z) {
+    if (y < 0.5 || z > 255.5) {
+        return {
+            type: BlockType.UNDEFINED,
+        }
+    }
     const midx = x + 0.5;
     const midy = y + 0.5;
     const midz = z + 0.5;
@@ -97,8 +103,7 @@ export function blockLookup(world, x, y, z) {
     const chunk = world.chunkMap.get(chunki, chunkj);
     if (chunk === undefined) {
         return {
-            type: BlockType.STONE,
-            centerPosition: [x, y, z],
+            type: BlockType.UNDEFINED,
         };
     }
 
@@ -121,6 +126,9 @@ function makeChunkBuffer(gl, data, z0, x0, blockLookup) {
         if (i < 0 || j < 0 || i > 15 || j > 15) {
             return blockLookup(i, j, k);
         }
+        if (k < 0 || k > 255) {
+            return BlockType.UNDEFINED;
+        }
         return data[256*(16*i + j) + k];
     };
     const sideNeighbors = (i, j, k) =>