Created
December 24, 2014 06:36
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| <!DOCTYPE html> | |
| <html> | |
| <head lang="en"> | |
| <meta charset="UTF-8"> | |
| <title>Dynamic Balls</title> | |
| <style> | |
| * { | |
| margin: 0; | |
| padding: 0; | |
| } | |
| </style> | |
| </head> | |
| <body style="height: 100%"> | |
| <canvas id="canvas" style="display: block;">Your browser doesn't support canvas!</canvas> | |
| <script type="application/javascript"> | |
| const WINDOW_WIDTH = window.innerWidth; | |
| const WINDOW_HEIGHT = window.innerHeight; | |
| window.onload = function () { | |
| var canvas = document.getElementById('canvas'); | |
| var context = canvas.getContext('2d'); | |
| canvas.width = WINDOW_WIDTH; | |
| canvas.height = WINDOW_HEIGHT; | |
| context.globalAlpha = 0.7; | |
| // context.globalCompositeOperation = 'lighter'; | |
| var balls = []; | |
| for (var i = 0; i < 100; i++) { | |
| var x = getRandomArbitrary(0, WINDOW_WIDTH); | |
| var y = getRandomArbitrary(0, WINDOW_HEIGHT); | |
| var vx = getRandomArbitrary(-10, 10); | |
| var vy = getRandomArbitrary(-10, 10); | |
| var r = getRandomArbitrary(0, 100); | |
| var color = getRandomColor(); | |
| var randomBall = { | |
| x: x, | |
| y: y, | |
| vx: vx, | |
| vy: vy, | |
| r: r, | |
| color: color | |
| }; | |
| balls.push(randomBall); | |
| } | |
| setInterval(function () { | |
| render(context, balls); | |
| update(context, balls); | |
| }, 50) | |
| }; | |
| function render(cxt, balls) { | |
| var canvas = cxt.canvas; | |
| cxt.clearRect(0, 0, canvas.width, canvas.height); | |
| for (var i = 0; i < balls.length; i++) { | |
| drawBall(balls[i].x, balls[i].y, balls[i].r, balls[i].color, cxt); | |
| } | |
| var string = 'Wishing you a Merry Christmas, Dear Miaomiao!'; | |
| var x = canvas.width - 20; | |
| var y = canvas.height - 20; | |
| drawText(string, x, y, cxt); | |
| } | |
| function update(cxt, balls) { | |
| var canvas = cxt.canvas; | |
| const canvasWidth = canvas.width; | |
| const canvasHeight = canvas.height; | |
| for (var i = 0; i < balls.length; i++) { | |
| var ball = balls[i]; | |
| ball.x += ball.vx; | |
| ball.y += ball.vy; | |
| // 左边缘检测 | |
| if (ball.x <= ball.r) { | |
| ball.x = ball.r; | |
| ball.vx = -ball.vx; | |
| } | |
| // 右边缘检测 | |
| if (ball.x >= (canvasWidth - ball.r)) { | |
| ball.x = canvasWidth - ball.r; | |
| ball.vx = -ball.vx; | |
| } | |
| // 上边缘检测 | |
| if (ball.y <= ball.r) { | |
| ball.y = ball.r; | |
| ball.vy = -ball.vy; | |
| } | |
| // 下边缘检测 | |
| if (ball.y >= (canvasHeight - ball.r)) { | |
| ball.y = canvasHeight - ball.r; | |
| ball.vy = - ball.vy; | |
| } | |
| } | |
| } | |
| function drawBall(x, y, r, color, cxt) { | |
| cxt.beginPath(); | |
| var startAngle = 0; | |
| var endAngle = 2 * Math.PI; | |
| cxt.arc(x, y, r, startAngle, endAngle); | |
| cxt.fillStyle = color; | |
| cxt.fill(); | |
| cxt.closePath(); | |
| } | |
| function drawText(string, x, y, cxt) { | |
| cxt.save(); | |
| cxt.font = '25px Papyrus'; | |
| cxt.fillStyle = '#FF36AD'; | |
| cxt.textAlign = 'right'; | |
| cxt.shadowColor = 'gray'; | |
| cxt.shadowOffsetX = 5; | |
| cxt.shadowOffsetY = 5; | |
| cxt.shadowBlur = 10; | |
| cxt.fillText(string, x, y); | |
| cxt.restore(); | |
| } | |
| function getRandomColor() { | |
| var color = ['#']; | |
| for (var i = 0; i < 6; i++) { | |
| color.push(parseInt(getRandomArbitrary(0, 17)).toString(16)); | |
| } | |
| return color.join(''); | |
| } | |
| function getRandomArbitrary(min, max) { | |
| return Math.random() * (max - min) + min; | |
| } | |
| </script> | |
| </body> | |
| </html> |
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