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<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>Orbit Draw</title>
<link rel="stylesheet" href="../include/style.css">
</head>
<body>
<header>
Example from <a href="http://amzn.com/1430236655?tag=html5anim-20"><em>Foundation HTML5 Animation with JavaScript</em></a>
</header>
<canvas id="canvas" width="400" height="400"></canvas>
<script src="../include/utils.js"></script>
<script src="./classes/ball.js"></script>
<script>
window.onload = function () {
var canvas = document.getElementById('canvas'),
context = canvas.getContext('2d'),
particles = [],
numParticles = 2,
sun = new Ball(100, "#ffff00"),
planet = new Ball(1, "#000000");
sun.x = canvas.width / 2;
sun.y = canvas.height / 2;
sun.mass = 10000;
particles.push(sun);
planet.x = canvas.width / 2 + 200;
planet.y = canvas.height / 2;
planet.vy = 7;
planet.mass = 1;
particles.push(planet);
function rotate (x, y, sin, cos, reverse) {
return {
x: (reverse) ? (x * cos + y * sin) : (x * cos - y * sin),
y: (reverse) ? (y * cos - x * sin) : (y * cos + x * sin)
};
}
function checkCollision (ball0, ball1) {
var dx = ball1.x - ball0.x,
dy = ball1.y - ball0.y,
dist = Math.sqrt(dx * dx + dy * dy);
//collision handling code here
if (dist < ball0.radius + ball1.radius) {
//calculate angle, sine, and cosine
var angle = Math.atan2(dy, dx),
sin = Math.sin(angle),
cos = Math.cos(angle),
//rotate ball0's position
pos0 = {x: 0, y: 0}, //point
//rotate ball1's position
pos1 = rotate(dx, dy, sin, cos, true),
//rotate ball0's velocity
vel0 = rotate(ball0.vx, ball0.vy, sin, cos, true),
//rotate ball1's velocity
vel1 = rotate(ball1.vx, ball1.vy, sin, cos, true),
//collision reaction
vxTotal = vel0.x - vel1.x;
vel0.x = ((ball0.mass - ball1.mass) * vel0.x + 2 * ball1.mass * vel1.x) /
(ball0.mass + ball1.mass);
vel1.x = vxTotal + vel0.x;
//update position - to avoid objects becoming stuck together
var absV = Math.abs(vel0.x) + Math.abs(vel1.x),
overlap = (ball0.radius + ball1.radius) - Math.abs(pos0.x - pos1.x);
pos0.x += vel0.x / absV * overlap;
pos1.x += vel1.x / absV * overlap;
//rotate positions back
var pos0F = rotate(pos0.x, pos0.y, sin, cos, false),
pos1F = rotate(pos1.x, pos1.y, sin, cos, false);
//adjust positions to actual screen positions
ball1.x = ball0.x + pos1F.x;
ball1.y = ball0.y + pos1F.y;
ball0.x = ball0.x + pos0F.x;
ball0.y = ball0.y + pos0F.y;
//rotate velocities back
var vel0F = rotate(vel0.x, vel0.y, sin, cos, false),
vel1F = rotate(vel1.x, vel1.y, sin, cos, false);
ball0.vx = vel0F.x;
ball0.vy = vel0F.y;
ball1.vx = vel1F.x;
ball1.vy = vel1F.y;
}
}
function gravitate (partA, partB) {
var dx = partB.x - partA.x,
dy = partB.y - partA.y,
distSQ = dx * dx + dy * dy,
dist = Math.sqrt(distSQ),
force = partA.mass * partB.mass / distSQ,
ax = force * dx / dist,
ay = force * dy / dist;
partA.vx += ax / partA.mass;
partA.vy += ay / partA.mass;
partB.vx -= ax / partB.mass;
partB.vy -= ay / partB.mass;
}
function move (partA, i) {
partA.x += partA.vx;
partA.y += partA.vy;
for (var partB, j = i + 1; j < numParticles; j++) {
partB = particles[j];
checkCollision(partA, partB);
gravitate(partA, partB);
}
}
function draw (particle) {
particle.draw(context);
}
(function drawFrame () {
window.requestAnimationFrame(drawFrame, canvas);
particles.forEach(move);
particles.forEach(draw);
}());
};
</script>
</body>
</html>