one-way platforms

src/entities/Platform.ts

@@ -10,4 +10,17 @@ export class Platform extends Phaser.GameObjects.Rectangle {
         scene.add.existing(this);
         scene.physics.add.existing(this, true);
     }
+
+    // Phaser collider processCallback: only collide when the mover is descending onto the top.
+    static canLand(
+        mover: Phaser.Types.Physics.Arcade.GameObjectWithBody,
+        platform: Phaser.Types.Physics.Arcade.GameObjectWithBody,
+    ): boolean {
+        const moverBody = mover.body as Phaser.Physics.Arcade.Body;
+        const platBody = platform.body as Phaser.Physics.Arcade.StaticBody;
+        return (
+            moverBody.velocity.y >= 0 &&
+            moverBody.bottom - moverBody.deltaY() <= platBody.top
+        );
+    }
 }

src/scenes/GameScene.ts

@@ -41,7 +41,7 @@ export class GameScene extends Phaser.Scene {
         this.exit = loaded.exit;
         this.platforms = loaded.platforms;
 
-        this.physics.add.collider(this.player, this.platforms);
+        this.physics.add.collider(this.player, this.platforms, undefined, Platform.canLand);
         this.physics.add.overlap(this.player, this.exit, () => this.completeLevel());
 
         this.hudText = this.add.text(