文章简介: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! |
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Jscex制作动画效果
var drawAsync = eval(Jscex.compile("async", function () {
while (true) {
context.drawImage(m_canvas, 0, 0);
$await(Jscex.Async.sleep(1000));
}
}))
drawAsync().start();
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