diff --git a/src/scenes/DrawScene.ts b/src/scenes/DrawScene.ts
index 41ded5d..b2edcb7 100644
--- a/src/scenes/DrawScene.ts
+++ b/src/scenes/DrawScene.ts
@@ -18,7 +18,7 @@ export default class DrawScene extends AbstractScene {
             uniforms: {
                 tWorld: { value: null },
                 pointerPosition: { value: new THREE.Vector2() },
-                drawMode: { value: 0 },
+                drawMode: { value: -1 },
                 brushRadius: { value: 0 },
             },
             vertexShader,
diff --git a/src/scenes/ScreenScene.ts b/src/scenes/ScreenScene.ts
index a4ea054..40bc485 100644
--- a/src/scenes/ScreenScene.ts
+++ b/src/scenes/ScreenScene.ts
@@ -1,5 +1,13 @@
 import * as THREE from "three";
 import Config from "../Config";
+import {
+    MAT_AIR,
+    MAT_DIRT,
+    MAT_FOOD,
+    MAT_HOME,
+    MAT_ROCK,
+    MAT_SAND,
+} from "../constants";
 import type Renderer from "../Renderer";
 import fragmentShaderAnts from "../shaders/ants.frag";
 import vertexShaderAnts from "../shaders/ants.vert";
@@ -7,21 +15,13 @@ import fragmentShaderGround from "../shaders/screenWorld.frag";
 import vertexShaderGround from "../shaders/screenWorld.vert";
 import AbstractScene from "./AbstractScene";
 
-enum PointerState {
-    None,
-    Food,
-    Home,
-    Obstacle,
-    Erase,
-}
-
 export default class ScreenScene extends AbstractScene {
     public readonly camera: THREE.OrthographicCamera;
     public readonly material: THREE.ShaderMaterial;
     public ants!: THREE.InstancedMesh;
     public readonly groundMaterial: THREE.ShaderMaterial;
     public readonly pointerPosition: THREE.Vector2 = new THREE.Vector2();
-    public drawMode: PointerState = PointerState.None;
+    public drawMode: number = -1;
     // zoom stored in Config.cameraZoom
     private isPointerDown: boolean = false;
     public renderWidth: number = 1;
@@ -148,26 +148,34 @@ export default class ScreenScene extends AbstractScene {
         window.addEventListener("keydown", (e) => {
             switch (e.code) {
                 case "KeyQ": {
-                    this.drawMode = PointerState.Home;
+                    this.drawMode = MAT_HOME;
                     break;
                 }
                 case "KeyW": {
-                    this.drawMode = PointerState.Food;
+                    this.drawMode = MAT_FOOD;
                     break;
                 }
                 case "KeyE": {
-                    this.drawMode = PointerState.Obstacle;
+                    this.drawMode = MAT_ROCK;
                     break;
                 }
                 case "KeyR": {
-                    this.drawMode = PointerState.Erase;
+                    this.drawMode = MAT_AIR;
+                    break;
+                }
+                case "Digit1": {
+                    this.drawMode = MAT_SAND;
+                    break;
+                }
+                case "Digit2": {
+                    this.drawMode = MAT_DIRT;
                     break;
                 }
             }
         });
 
         window.addEventListener("keyup", () => {
-            this.drawMode = PointerState.None;
+            this.drawMode = -1;
         });
     }
 
diff --git a/src/shaders/draw.frag b/src/shaders/draw.frag
index 483942e..bae8c11 100644
--- a/src/shaders/draw.frag
+++ b/src/shaders/draw.frag
@@ -13,24 +13,12 @@ uniform float brushRadius;
 void main()	{
     vec4 lastState = texture(tWorld, vUv);
 
-    int cellData = int(lastState.x);
-    int isFood = cellData & 1;
-    int isHome = (cellData & 2) >> 1;
-    int isObstacle = (cellData & 4) >> 2;
+    float materialId = lastState.x;
 
-    if (distance(pointerPosition, vUv) < brushRadius / WORLD_SIZE) {
-        if (drawMode == 1.) {
-            isFood = 1;
-        } else if (drawMode == 2.) {
-            isHome = 1;
-        } else if (drawMode == 3.) {
-            isObstacle = 1;
-        } else if (drawMode == 4.) {
-            isFood = 0;
-            isHome = 0;
-            isObstacle = 0;
-        }
+    // drawMode >= 0 means painting that material ID; -1 means not drawing
+    if (drawMode >= 0. && distance(pointerPosition, vUv) < brushRadius / WORLD_SIZE) {
+        materialId = drawMode;
     }
 
-    FragColor = vec4(float(isFood + (isHome << 1) + (isObstacle << 2)), lastState.yzw);
-}
\ No newline at end of file
+    FragColor = vec4(materialId, lastState.yzw);
+}