Testing requestAnimationFrame

2021-11-10 21:58:35 +01:00
commit 56c478d614
2 changed files with 77 additions and 0 deletions
--- a/index.html
+++ b/index.html
@ -0,0 +1,8 @@
 <html>
 <head>
 <script src="index.js"></script>
 </head>
 <body>
 <canvas id="canvas"></canvas>
 </body>
 </html>
--- a/index.js
+++ b/index.js
@ -0,0 +1,69 @@
 "use strict";
 document.addEventListener('DOMContentLoaded', init);
 function init() {
    var canvas = document.getElementById("canvas");
    canvas.width = window.innerWidth
    canvas.height = window.innerHeight
    const ctx = canvas.getContext('2d');
    var balls = [];
    add();
    document.addEventListener('keydown', control);
    anim();
    function control(e) {
        switch(e.key) {
            case 'ArrowUp':     add();   break;
            case 'ArrowDown':   remove(); break;
        }        
    }
    function remove() {
        balls.pop();
    }
    function add() {
        let x = Math.floor(Math.random() * canvas.width);
        let y = Math.floor(Math.random() * canvas.height);
        let speed = 1 + Math.floor(Math.random() * 10);
        let angle = Math.floor(Math.random() * 360);
        // angle must be in radians (now it's wrong)
        balls.push({ x: x, y: y, size: 20, speed: speed, angle: angle, color:'black' });
    }
    function anim() {
        ctx.fillStyle = 'white';
        ctx.fillRect(0, 0, canvas.width, canvas.height);
        balls.forEach(b => {
            update(b);
            draw(b);
        }
        );
        requestAnimationFrame(anim);
    }
    function update(b) {
        b.x += b.speed * Math.cos(b.angle);
        b.y += b.speed * Math.sin(b.angle);
        if ( b.x<0 || b.x>canvas.width || b.y<0 || b.y>canvas.height ) bounce(b);
    }
    function bounce(b) {
        b.angle += 180; 
    }
    function draw(b) {
        ctx.fillStyle = b.color;
        ctx.fillRect(b.x, b.y, b.size, b.size);
    }
 }