100 lines
2.7 KiB
Markdown
100 lines
2.7 KiB
Markdown
---
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title: Particle Sim
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---
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## Particle Simulation in Canvas
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In this guide, we're going to build a basic particle simulation in Canvas using simple principles of animation.
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We will want to set up an array of particles with accelerations and velocities. We will create 100 particles at random points on the canvas.
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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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In our draw loop, we render these particles.
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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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Now, all we need to do is update velocity and acceleration each frame. We will add the acceleration to the velocity and add the velocity to the position.
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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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That's it! All we need to do to is create a force somewhere. Let's do it with a click listener.
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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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This adds force via the inverse-square law. See [this page](#placeholder) for more details.
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That's all! The final codepen:
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<p data-height="265" data-theme-id="0" data-slug-hash="OjMbpm" data-default-tab="js,result" data-user="alanluo" data-embed-version="2" data-pen-title="Particle Sim (FCC)" class="codepen">See the Pen <a href="https://codepen.io/alanluo/pen/OjMbpm/">Particle Sim (FCC)</a> by Alan Luo (<a href="https://codepen.io/alanluo">@alanluo</a>) on <a href="https://codepen.io">CodePen</a>.</p>
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<script async src="https://production-assets.codepen.io/assets/embed/ei.js"></script>
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<!-- TODO: make it cooler! -->
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#### More Information:
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- [MDN Canvas API](https://developer.mozilla.org/en-US/docs/Web/API/Canvas_API)
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