你还在抱怨自己写的canvas demo徘徊在10帧以下吗?你还在烦恼打开自己写的应用就听见CUP风扇转吗?你正在写一个javascript Canvas库吗?那么下面九点就是你必须知道的!
一.预渲染
错误代码:
var canvas = document.getElementById("myCanvas");
var context = this.canvas.getContext('2d');
var drawAsync = eval(Jscex.compile("async", function () { while (true) { drawMario(context); $await(Jscex.Async.sleep(1000)); } }))
drawAsync().start();
正确代码:
var canvas = document.getElementById("myCanvas");
var context = this.canvas.getContext('2d');
var m_canvas = document.createElement('canvas');
m_canvas.width = 64; m_canvas.height = 64;
var m_context = m_canvas.getContext('2d');
drawMario(m_context);
var drawAsync = eval(Jscex.compile("async", function () {while (true) {context.drawImage(m_canvas, 0, 0);
$await(Jscex.Async.sleep(1000));}}))
drawAsync().start();
这里m_canvas的宽度和高度控制得越小越好。
二.尽量少调用canvasAPI
错误代码:
for (var i = 0; i < points.length - 1; i++) { var p1 = points[i]; var p2 = points[i + 1]; context.beginPath();
context.moveTo(p1.x, p1.y); context.lineTo(p2.x, p2.y); context.stroke(); }
正确代码:
context.beginPath(); for (var i = 0; i < points.length - 1; i++) {var p1 = points[i];
var p2 = points[i + 1]; context.moveTo(p1.x, p1.y);
context.lineTo(p2.x, p2.y); }
context.stroke();
三.尽量少改变CANVAS状态
错误代码:
for (var i = 0; i < STRIPES; i++) {
context.fillStyle = (i % 2 ? COLOR1 : COLOR2);
context.fillRect(i * GAP, 0, GAP, 480); }
正确代码:
context.fillStyle = COLOR1;
for (var i = 0; i < STRIPES / 2; i++) {context.fillRect((i * 2) * GAP, 0, GAP, 480);}
context.fillStyle = COLOR2;
for (var i = 0; i < STRIPES / 2; i++) {context.fillRect((i * 2 + 1) * GAP, 0, GAP, 480);}
四.重新渲染的范围尽量小
错误代码:context.fillRect(0, 0, canvas.width, canvas.height);
正确代码:context.fillRect(20, 20, 100, 100);
五.复杂场景使用多层画布
<canvas width="600" height="400" style="position: absolute; z-index: 0"> </canvas>
<canvas width="600" height="400" style="position: absolute; z-index: 1"> </canvas>
六.不要使用阴影
context.shadowOffsetX = 5;
context.shadowOffsetY = 5;
context.shadowBlur = 4;
context.shadowColor = 'rgba(255, 0, 0, 0.5)';
context.fillRect(20, 20, 150, 100);
七.清除画布
详细性能差别:http://simonsarris.com/blog/346-how-you-clear-your-canvas-matters
一般情况下:clearRect的性能优于fillRect优于canvas.width = canvas.width;
八.像素级别操作尽量用整数
几种取整数的方法:
rounded = (0.5 + somenum) | 0; rounded = ~ ~(0.5 + somenum); rounded = (0.5 + somenum) << 0;
九.使用requestAnimationFrame制作游戏或动画
(function () {
var lastTime = 0;
var vendors = ['ms', 'moz', 'webkit', 'o'];
for (var x = 0; x < vendors.length && !window.requestAnimationFrame; ++x) {
window.requestAnimationFrame = window[vendors[x] + 'RequestAnimationFrame'];
window.cancelAnimationFrame =
window[vendors[x] + 'CancelAnimationFrame'] || window[vendors[x] + 'CancelRequestAnimationFrame'];
}
if (!window.requestAnimationFrame)
window.requestAnimationFrame = function (callback, element) {
var currTime = new Date().getTime();
var timeToCall = Math.max(0, 16 - (currTime - lastTime));
var id = window.setTimeout(function () { callback(currTime + timeToCall); },
timeToCall);
lastTime = currTime + timeToCall;
return id;};
if (!window.cancelAnimationFrame)
window.cancelAnimationFrame = function (id) {
clearTimeout(id);
};
} ());
十.其他
与渲染无关的计算交给worker
复杂的计算交给引擎(自己写,或者用开源的),比如3D、物理
缓存load好的图片,canvas上画canvas,而不是画image
来源 博客园
版权声明:本文由[当耐特]发表于 https://www.cnblogs.com/iamzhanglei/archive/2011/11/29/2267868.html