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4_collisions_elastic.html
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<!DOCTYPE html><html><head><meta charset="utf-8"><title>Skookum Labs</title></head><body><canvas id="surface" width="600" height="400"></canvas><pre><code id="source">var ball = {
x: 300,
y: 200,
r: 15,
vx: 0,
vy: 0
};
|
// ...
|
ball.x += ball.vx;
ball.y += ball.vy;
|
ball.vx *= .99;
ball.vy *= .99;
|
ball.vy += .25;
|
if (ball.y + ball.r > canvas.height) {
ball.y = canvas.height - ball.r;
ball.vy = -Math.abs(ball.vy);
}
</code></pre><script>// Version 3 - Basic collision (viewbox), perfectly elastic (no energy loss)
var ball = {
x: 300,
y: 200,
r: 15,
vx: 0,
vy: 0
};
var canvas = document.getElementById("surface");
var ctx = canvas.getContext('2d');
setInterval(function() {
// Clear display
ctx.save();
ctx.fillStyle = "rgba(0, 0, 0, .3)";
ctx.fillRect(0, 0, canvas.width, canvas.height);
ctx.restore();
// Update ball (with Physics! =)
// 1 - apply velocity to position (vx -> x)
ball.x += ball.vx;
ball.y += ball.vy;
// 2 - apply drag/friction to velocity
ball.vx *= .99;
ball.vy *= .99;
// 3 - apply gravity to velocity
ball.vy += .25;
// 4 - check for collisions
if (ball.y + ball.r > canvas.height) {
ball.y = canvas.height - ball.r;
ball.vy = -Math.abs(ball.vy);
}
// Draw ball
ctx.save();
ctx.translate(ball.x, ball.y);
ctx.fillStyle = "#fff";
ctx.beginPath();
ctx.arc(0, 0, ball.r, 0, Math.PI * 2, true);
ctx.closePath();
ctx.fill();
ctx.restore();
}, 1000 / 77);
</script></body></html>