95 lines
2.4 KiB
Markdown
95 lines
2.4 KiB
Markdown
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---
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title: Particle Sim
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localeTitle: 粒子是的
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---
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## 画布中的粒子模拟
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在本指南中，我们将使用简单的动画原理在Canvas中构建基本粒子模拟。
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我们想要建立一个具有加速度和速度的粒子阵列。我们将在画布上的随机点创建100个粒子。
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```js
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canvas = document.getElementById("canvas");
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ctx = canvas.getContext('2d');
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var particles = [];
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for(var i=0; i<100; i++) {
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particles.push(
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{
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x:Math.random()*canvas.width,
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y:Math.random()*canvas.height,
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vx:0,
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vy:0,
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ax:0,
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ay:0
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}
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);
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}
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```
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在我们的绘制循环中，我们渲染这些粒子。
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```js
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function draw() {
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ctx.clearRect(0, 0, canvas.width, canvas.height);
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for(var i=0; i<particles.length; i++) {
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// update state
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// render state
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ctx.beginPath();
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ctx.arc(particles[i].x, particles[i].y, 5, 0, 2*Math.PI);
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ctx.fill();
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}
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window.requestAnimationFrame(draw);
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}
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window.requestAnimationFrame(draw);
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```
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现在，我们需要做的就是每帧更新速度和加速度。我们将加速度添加到速度并将速度添加到位置。
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```js
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function draw() {
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for(var i=0; i<particles.length; i++) {
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// update state
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particles[i].x+=particles[i].vx;
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particles[i].y+=particles[i].vy;
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particles[i].vx+=particles[i].ax;
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particles[i].vy+=particles[i].ay;
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/* render code */
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}
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window.requestAnimationFrame(draw);
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}
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window.requestAnimationFrame(draw);
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```
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而已！我们需要做的就是在某处创造一股力量。让我们用点击监听器来做。
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```js
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canvas.addEventListener("click", function(e) {
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var clickX = e.clientX-canvas.offsetLeft;
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var clickY = e.clientY-canvas.offsetTop;
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for(var i=0; i<particles.length; i++) {
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var delx = particles[i].x-clickX;
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var dely = particles[i].y-clickY;
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var magnitudeSquared = Math.pow(delx, 2)+Math.pow(dely, 2);
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particles[i].ax = 0.1*delx/magnitudeSquared;
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particles[i].ay = 0.1*dely/magnitudeSquared;
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}
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});
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```
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这通过平方反比定律增加了力。有关详细信息，请参阅[此页面](#placeholder) 。
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就这样！最终的代码：
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见笔[粒子SIM（FCC）](https://codepen.io/alanluo/pen/OjMbpm/)由罗志祥（ [@alanluo](https://codepen.io/alanluo)上） [CodePen](https://codepen.io) 。
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#### 更多信息：
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* [MDN Canvas API](https://developer.mozilla.org/en-US/docs/Web/API/Canvas_API)
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