Planck.jsサンプルコード 物体をマウスでつまむ

2D物理エンジンPlanck.jsのサンプルコードを書きました。物体をマウスでつまんで動かします。

サンプルコード

<canvas id="canvas" width="400" height="400" style="border:solid"></canvas>

<script src="planck.js"></script>

<script>

var World = planck.World,
	Vec2 = planck.Vec2,
	Edge = planck.Edge,
	Box = planck.Box,
	Transform = planck.Transform;


class Demo{
	constructor(){
		this.world = this._createWorld();
		this._initializeGround(this.world);
		this._initializeBox(this.world);
		this._initializeInput();
	}

	_initializeInput(){
		canvas.onmousemove = (e) => {
			this.mousePosition = Vec2(e.offsetX, e.offsetY);
		};

		canvas.onmousedown = (e) => {
			if(!this.isMouseOverBox){	return;	}

			this.localDragPosition = Transform.mul(
				new Transform(Vec2(), -this.box.getTransform().q.getAngle()), 
				Vec2(e.offsetX, e.offsetY).sub(this.box.getPosition())
				);
		};

		canvas.onmouseup = () => {
			this.localDragPosition = null;
		};
	}

	get isMouseOverBox(){
		return this.boxShape.testPoint(this.box.getTransform(), this.mousePosition)
	}

	get isMouseButtonDown(){
		return this.localDragPosition != null;
	}

	_createWorld(){
		var world = World();
		world.setGravity(Vec2(0, 100));
		return world;
	}

	_initializeGround(world){
		var ground = world.createBody();
		ground.createFixture(Edge(Vec2(0, canvas.height), Vec2(400, canvas.height)));
	}

	_initializeBox(world){
		this.box = world.createBody().setDynamic();
		this.box.setPosition(Vec2(200, 100));

		this.boxShape = Box(10, 40);
		this.box.createFixture(this.boxShape);
		this.box.setMassData(this._getMassData(this.boxShape));
		this.box.setAngle(Math.PI / 6);
	}

	_getMassData(boxShape){
		var massData = {center:Vec2()};
		boxShape.computeMass(massData, 1);
		return massData;
	}

	run(){
		window.requestAnimationFrame(() => this.run());
		this._update();
		this._draw();
	}

	_update(){
		if(this.isMouseButtonDown){
			this.worldDragPosition = Transform.mul(this.box.getTransform(), this.localDragPosition);
			this.box.applyForce(
				this.mousePosition.clone().sub(this.worldDragPosition).mul(10000), 
				this.worldDragPosition, 
				true);
		}

		this.world.step(1 / 60);
	}

	_draw(){
		var context = canvas.getContext("2d");
		context.clearRect(0, 0, canvas.width, canvas.height);

		this._drawBox(context);
		this._drawDragString(context);
	}

	_drawDragString(context){
		if(this.isMouseButtonDown){
			context.strokeStyle = "orange";
			context.lineWidth = 3;
			context.beginPath();
			context.moveTo(this.worldDragPosition.x, this.worldDragPosition.y);
			context.lineTo(this.mousePosition.x, this.mousePosition.y);
			context.stroke();
		}
	}

	_drawBox(context){
		for(var fixture = this.box.getFixtureList(); fixture; fixture = fixture.getNext()){
			context.beginPath();

			for(var vertex of fixture.getShape().m_vertices){
				var transformedPosition = Transform.mul(this.box.getTransform(), vertex);
				context.lineTo(transformedPosition.x, transformedPosition.y);
			}

			context.fill();
		}
	}
}


function main(){
	var demo = new Demo();
	demo.run();
}

main();

</script>

実行結果

解説

このプログラムは、物体をマウスでつまんで自由に動かすデモです。マウスを黒いブロックの上に持っていって、ドラッグしてみて下さい。オレンジ色の線が描かれます。このオレンジの線はゴム紐のような性質を持っていて、ひっぱるとブロックがそちら側に引っ張られます。伸びれば伸びるほど、引っ張る力は強くなります。