你必須知道的10個(gè)提高Canvas性能技巧

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你必須知道的10個(gè)提高Canvas性能技巧

你必須知道的10個(gè)提高Canvas性能技巧:你還在抱怨自己寫(xiě)的canvas demo徘徊在10幀以下嗎？你還在煩惱打開(kāi)自己寫(xiě)的應(yīng)用就聽(tīng)見(jiàn)CUP風(fēng)扇轉(zhuǎn)嗎？你正在寫(xiě)一個(gè)javascript Canvas庫(kù)嗎？那么下面九點(diǎn)就是你必須知道的！一.預(yù)渲染錯(cuò)誤代碼： var canvas = document.getElementById

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導(dǎo)讀你必須知道的10個(gè)提高Canvas性能技巧:你還在抱怨自己寫(xiě)的canvas demo徘徊在10幀以下嗎？你還在煩惱打開(kāi)自己寫(xiě)的應(yīng)用就聽(tīng)見(jiàn)CUP風(fēng)扇轉(zhuǎn)嗎？你正在寫(xiě)一個(gè)javascript Canvas庫(kù)嗎？那么下面九點(diǎn)就是你必須知道的！一.預(yù)渲染錯(cuò)誤代碼： var canvas = document.getElementById

你還在抱怨自己寫(xiě)的canvas demo徘徊在10幀以下嗎？你還在煩惱打開(kāi)自己寫(xiě)的應(yīng)用就聽(tīng)見(jiàn)CUP風(fēng)扇轉(zhuǎn)嗎？你正在寫(xiě)一個(gè)javascript Canvas庫(kù)嗎？那么下面九點(diǎn)就是你必須知道的！一.預(yù)渲染錯(cuò)誤代碼： var canvas = document.getElementById( "myCanvas" ); var cont

一.預(yù)渲染

錯(cuò)誤代碼：

 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();

正確代碼：

 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();

這里m_canvas的寬度和高度控制得越小越好。

二.盡量少調(diào)用canvasAPI

錯(cuò)誤代碼：

 
 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();
 }

正確代碼：

 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.盡量少改變CANVAS狀態(tài)

錯(cuò)誤代碼：

 for (var i = 0; i < STRIPES; i++) {
 context.fillStyle = (i % 2 ? COLOR1 : COLOR2);
 context.fillRect(i * GAP, 0, GAP, 480);
 }

正確代碼：

 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.重新渲染的范圍盡量小

錯(cuò)誤代碼：

 context.fillRect(0, 0, canvas.width, canvas.height);

正確代碼：

 context.fillRect(20, 20, 100, 100);

五.復(fù)雜場(chǎng)景使用多層畫(huà)布

六.不要使用陰影

 context.shadowOffsetX = 5;
 context.shadowOffsetY = 5;
 context.shadowBlur = 4;
 context.shadowColor = 'rgba(255, 0, 0, 0.5)';
 context.fillRect(20, 20, 150, 100);

七.清除畫(huà)布

詳細(xì)性能差別：
http://simonsarris.com/blog/346-how-you-clear-your-canvas-matters
一般情況下：clearRect的性能優(yōu)于fillRect優(yōu)于canvas.width = canvas.width;

八.像素級(jí)別操作盡量用整數(shù)

幾種取整數(shù)的方法：

rounded = (0.5 + somenum) | 0;
rounded = ~ ~(0.5 + somenum);
rounded = (0.5 + somenum) << 0;

九.使用requestAnimationFrame制作游戲或動(dòng)畫(huà)

 (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);
 };
 } ());