来源 | https://www.kancloud.cn/digest/canvas-programming/154008
小试牛刀，实现了六款简单常见HTML5 Canvas特效滤镜，并且封装成一个纯JavaScript可调用的API文件gloomyfishfilter.js。支持的特效滤镜分别为：
2.灰色调：获取一个预期点RGB值r，g，b则新的RGB值
newr =（r * 0.272）+（g * 0.534）+（b * 0.131）;
newg =（r * 0.349）+（g * 0.686）+（b * 0.168）;
newb =（r * 0.393）+（g * 0.769）+（b * 0.189）;
根据当前预期的前一个预期RGB值与它的后一个重新的RGB值之差再加上128
1、如何获取Canvas 2d context对象
var canvas = document.getElementById("target");
canvas.width = source.clientWidth;
canvas.height = source.clientHeight;
**if**(!canvas.getContext) {
console.log("Canvas not supported. Please install a HTML5compatible browser.");
**return**;
}
// get 2D context of canvas and draw image
tempContext = canvas.getContext("2d");
2、如何添加一个DOM img对象到Canvas对象中
var source = document.getElementById("source");
tempContext.drawImage(source, 0, 0, canvas.width,canvas.height);
var canvas = document.getElementById("target");
var len = canvas.width * canvas.height * 4;
var canvasData = tempContext.getImageData(0, 0, canvas.width, canvas.height);
var binaryData = canvasData.data;
4、如何对DOM对象实现鼠标ClickEvent绑定
function bindButtonEvent(element, type, handler) {
if(element.addEventListener){
element.addEventListener(type, handler,**false**);
}else{
element.attachEvent('on'+type, handler);// for IE6,7,8
}
}
5、如何调用实现的gfilter API完成滤镜功能
<scriptsrc=*"gloomyfishfilter.js"*></script> //导入API文件
gfilter.colorInvertProcess(binaryData, len); //调用 API
6、浏览器支持：IE，FF，Chrome上测试通过，其中IE上支持通过以下标签实现：
<meta http-equiv="X-UA-Compatible"*content=*"chrome=IE8">
#svgContainer { width:800px; height:600px; background-color:#EEEEEE;}
#sourceDiv { float: left; border: 2px solid blue} #targetDiv { float: right;border: 2px solid red}
<!DOCTYPE html><html><head><meta http-equiv="X-UA-Compatible" content="chrome=IE8"><meta http-equiv="Content-type" content="text/html;charset=UTF-8"><title>Canvas Filter Demo</title><link href="default.css" rel="stylesheet" /><script src="gloomyfishfilter.js"></scrip></head><body> <h1>HTML Canvas Image Process - By Gloomy Fish</h1> <div id="svgContainer"> <div id="sourceDiv"> <img id="source" src="../test.png" /> </div> <div id="targetDiv"> <canvas id="target"></canvas> </div> </div> <div id="btn-group"> <button type="button" id="invert-button">反色</button> <button type="button" id="adjust-button">灰色调</button> <button type="button" id="blur-button">模糊</button> <button type="button" id="relief-button">浮雕</button> <button type="button" id="diaoke-button">雕刻</button> <button type="button" id="mirror-button">镜像</button> </div></body></html>
filter1.html中JavaScript源代码：
var tempContext = null; // global variable 2d context window.onload = function() { var source = document.getElementById("source"); var canvas = document.getElementById("target"); canvas.width = source.clientWidth; canvas.height = source.clientHeight;
if (!canvas.getContext) { console.log("Canvas not supported. Please install a HTML5 compatible browser."); return; }
// get 2D context of canvas and draw image tempContext = canvas.getContext("2d"); tempContext.drawImage(source, 0, 0, canvas.width, canvas.height);
// initialization actions var inButton = document.getElementById("invert-button"); var adButton = document.getElementById("adjust-button"); var blurButton = document.getElementById("blur-button"); var reButton = document.getElementById("relief-button"); var dkButton = document.getElementById("diaoke-button"); var mirrorButton = document.getElementById("mirror-button");
// bind mouse click event bindButtonEvent(inButton, "click", invertColor); bindButtonEvent(adButton, "click", adjustColor); bindButtonEvent(blurButton, "click", blurImage); bindButtonEvent(reButton, "click", fudiaoImage); bindButtonEvent(dkButton, "click", kediaoImage); bindButtonEvent(mirrorButton, "click", mirrorImage); }
function bindButtonEvent(element, type, handler) { if(element.addEventListener) { element.addEventListener(type, handler, false); } else { element.attachEvent('on'+type, handler); // for IE6,7,8 } }
function invertColor() { var canvas = document.getElementById("target"); var len = canvas.width * canvas.height * 4; var canvasData = tempContext.getImageData(0, 0, canvas.width, canvas.height); var binaryData = canvasData.data;
// Processing all the pixels gfilter.colorInvertProcess(binaryData, len);
// Copying back canvas data to canvas tempContext.putImageData(canvasData, 0, 0); }
function adjustColor() { var canvas = document.getElementById("target"); var len = canvas.width * canvas.height * 4; var canvasData = tempContext.getImageData(0, 0, canvas.width, canvas.height); var binaryData = canvasData.data;
// Processing all the pixels gfilter.colorAdjustProcess(binaryData, len);
// Copying back canvas data to canvas tempContext.putImageData(canvasData, 0, 0); }
function blurImage() { var canvas = document.getElementById("target"); var len = canvas.width * canvas.height * 4; var canvasData = tempContext.getImageData(0, 0, canvas.width, canvas.height);
// Processing all the pixels gfilter.blurProcess(tempContext, canvasData);
// Copying back canvas data to canvas tempContext.putImageData(canvasData, 0, 0); }
function fudiaoImage() { var canvas = document.getElementById("target"); var len = canvas.width * canvas.height * 4; var canvasData = tempContext.getImageData(0, 0, canvas.width, canvas.height);
// Processing all the pixels gfilter.reliefProcess(tempContext, canvasData);
// Copying back canvas data to canvas tempContext.putImageData(canvasData, 0, 0); }
function kediaoImage() { var canvas = document.getElementById("target"); var len = canvas.width * canvas.height * 4; var canvasData = tempContext.getImageData(0, 0, canvas.width, canvas.height);
// Processing all the pixels gfilter.diaokeProcess(tempContext, canvasData);
// Copying back canvas data to canvas tempContext.putImageData(canvasData, 0, 0); }
function mirrorImage() { var canvas = document.getElementById("target"); var len = canvas.width * canvas.height * 4; var canvasData = tempContext.getImageData(0, 0, canvas.width, canvas.height);
// Processing all the pixels gfilter.mirrorProcess(tempContext, canvasData);
// Copying back canvas data to canvas tempContext.putImageData(canvasData, 0, 0); }
滤镜源代码（gloomyfishfilter.js）：
var gfilter = { type: "canvas", name: "filters", author: "zhigang", getInfo: function () { return this.author + ' ' + this.type + ' ' + this.name; },
/** * invert color value of pixel, new pixel = RGB(255-r, 255-g, 255 - b) * * @param binaryData - canvas's imagedata.data * @param l - length of data (width * height of image data) */ colorInvertProcess: function(binaryData, l) { for (var i = 0; i < l; i += 4) { var r = binaryData[i]; var g = binaryData[i + 1]; var b = binaryData[i + 2];
binaryData[i] = 255-r; binaryData[i + 1] = 255-g; binaryData[i + 2] = 255-b; } },
/** * adjust color values and make it more darker and gray... * * @param binaryData * @param l */ colorAdjustProcess: function(binaryData, l) { for (var i = 0; i < l; i += 4) { var r = binaryData[i]; var g = binaryData[i + 1]; var b = binaryData[i + 2];
binaryData[i] = (r * 0.272) + (g * 0.534) + (b * 0.131); binaryData[i + 1] = (r * 0.349) + (g * 0.686) + (b * 0.168); binaryData[i + 2] = (r * 0.393) + (g * 0.769) + (b * 0.189); } },
/** * deep clone image data of canvas * * @param context * @param src * @returns */ copyImageData: function(context, src) { var dst = context.createImageData(src.width, src.height); dst.data.set(src.data); return dst; },
/** * convolution - keneral size 5*5 - blur effect filter(模糊效果) * * @param context * @param canvasData */ blurProcess: function(context, canvasData) { console.log("Canvas Filter - blur process"); var tempCanvasData = this.copyImageData(context, canvasData); var sumred = 0.0, sumgreen = 0.0, sumblue = 0.0; for ( var x = 0; x < tempCanvasData.width; x++) { for ( var y = 0; y < tempCanvasData.height; y++) {
// Index of the pixel in the array var idx = (x + y * tempCanvasData.width) * 4; for(var subCol=-2; subCol<=2; subCol++) { var colOff = subCol + x; if(colOff <0 || colOff >= tempCanvasData.width) { colOff = 0; } for(var subRow=-2; subRow<=2; subRow++) { var rowOff = subRow + y; if(rowOff < 0 || rowOff >= tempCanvasData.height) { rowOff = 0; } var idx2 = (colOff + rowOff * tempCanvasData.width) * 4; var r = tempCanvasData.data[idx2 + 0]; var g = tempCanvasData.data[idx2 + 1]; var b = tempCanvasData.data[idx2 + 2]; sumred += r; sumgreen += g; sumblue += b; } }
// calculate new RGB value var nr = (sumred / 25.0); var ng = (sumgreen / 25.0); var nb = (sumblue / 25.0);
// clear previous for next pixel point sumred = 0.0; sumgreen = 0.0; sumblue = 0.0;
// assign new pixel value canvasData.data[idx + 0] = nr; // Red channel canvasData.data[idx + 1] = ng; // Green channel canvasData.data[idx + 2] = nb; // Blue channel canvasData.data[idx + 3] = 255; // Alpha channel } } },
/** * after pixel value - before pixel value + 128 * 浮雕效果 */ reliefProcess: function(context, canvasData) { console.log("Canvas Filter - relief process"); var tempCanvasData = this.copyImageData(context, canvasData); for ( var x = 1; x < tempCanvasData.width-1; x++) { for ( var y = 1; y < tempCanvasData.height-1; y++) {
// Index of the pixel in the array var idx = (x + y * tempCanvasData.width) * 4; var bidx = ((x-1) + y * tempCanvasData.width) * 4; var aidx = ((x+1) + y * tempCanvasData.width) * 4;
// calculate new RGB value var nr = tempCanvasData.data[aidx + 0] - tempCanvasData.data[bidx + 0] + 128; var ng = tempCanvasData.data[aidx + 1] - tempCanvasData.data[bidx + 1] + 128; var nb = tempCanvasData.data[aidx + 2] - tempCanvasData.data[bidx + 2] + 128; nr = (nr < 0) ? 0 : ((nr >255) ? 255 : nr); ng = (ng < 0) ? 0 : ((ng >255) ? 255 : ng); nb = (nb < 0) ? 0 : ((nb >255) ? 255 : nb);
// assign new pixel value canvasData.data[idx + 0] = nr; // Red channel canvasData.data[idx + 1] = ng; // Green channel canvasData.data[idx + 2] = nb; // Blue channel canvasData.data[idx + 3] = 255; // Alpha channel } } },
/** * before pixel value - after pixel value + 128 * 雕刻效果 * * @param canvasData */ diaokeProcess: function(context, canvasData) { console.log("Canvas Filter - process"); var tempCanvasData = this.copyImageData(context, canvasData); for ( var x = 1; x < tempCanvasData.width-1; x++) { for ( var y = 1; y < tempCanvasData.height-1; y++) {
// Index of the pixel in the array var idx = (x + y * tempCanvasData.width) * 4; var bidx = ((x-1) + y * tempCanvasData.width) * 4; var aidx = ((x+1) + y * tempCanvasData.width) * 4;
// calculate new RGB value var nr = tempCanvasData.data[bidx + 0] - tempCanvasData.data[aidx + 0] + 128; var ng = tempCanvasData.data[bidx + 1] - tempCanvasData.data[aidx + 1] + 128; var nb = tempCanvasData.data[bidx + 2] - tempCanvasData.data[aidx + 2] + 128; nr = (nr < 0) ? 0 : ((nr >255) ? 255 : nr); ng = (ng < 0) ? 0 : ((ng >255) ? 255 : ng); nb = (nb < 0) ? 0 : ((nb >255) ? 255 : nb);
// assign new pixel value canvasData.data[idx + 0] = nr; // Red channel canvasData.data[idx + 1] = ng; // Green channel canvasData.data[idx + 2] = nb; // Blue channel canvasData.data[idx + 3] = 255; // Alpha channel } } },
/** * mirror reflect * * @param context * @param canvasData */ mirrorProcess : function(context, canvasData) { console.log("Canvas Filter - process"); var tempCanvasData = this.copyImageData(context, canvasData); for ( var x = 0; x < tempCanvasData.width; x++) // column { for ( var y = 0; y < tempCanvasData.height; y++) // row {
// Index of the pixel in the array var idx = (x + y * tempCanvasData.width) * 4; var midx = (((tempCanvasData.width -1) - x) + y * tempCanvasData.width) * 4;
// assign new pixel value canvasData.data[midx + 0] = tempCanvasData.data[idx + 0]; // Red channel canvasData.data[midx + 1] = tempCanvasData.data[idx + 1]; ; // Green channel canvasData.data[midx + 2] = tempCanvasData.data[idx + 2]; ; // Blue channel canvasData.data[midx + 3] = 255; // Alpha channel } } },};
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