CHROME扩展笔记之图标设置(彩色和灰色的切换)

// 返回灰色画布
function grey_img(src,callback){
　　/*创建一个canvas*/
    var canvas=document.createElement('canvas');
    var ctx=canvas.getContext('2d');
    var img=new Image();
    img.src=src;
    img.onload = function(){
        // 因为图片加载时异步的，所以需要采用回调的方式，不然图片宽高读取会变成0导致 Failed to execute 'getImageData' on 'CanvasRenderingContext2D' 报错
        canvas.height=img.height;
        canvas.width=img.width;
        ctx.drawImage(img,0,0);
        var imgdata=ctx.getImageData(0,0,canvas.width,canvas.height);var data=imgdata.data;
        /*灰度处理：求r，g，b的均值，并赋回给r，g，b*/
        for(var i=0,n=data.length;i<n;i+=4){
            var average=(data[i]+data[i+1]+data[i+2])/3;
            data[i]=average;
            data[i+1]=average;
            data[i+2]=average;
        }
        ctx.putImageData(imgdata,0,0);
        if(typeof callback === 'function'){
            /*将处理后的回调给调用者*/
            callback({canvas,ctx});
        }
    }
}
// 灰图变量
var grey_img_icon = null;
var Cicon_state = null;
// 设置图标函数
function switch_icon(_on_off){
    _on_off = !zsl.empty(_on_off);
    if(Cicon_state !== _on_off){
        let path = 'img/icon_128.png';
        Cicon_state = _on_off;
        if(_on_off){
            // 恢复正常图标
            chrome.browserAction.setIcon({
                path
            });
            // 启动程序
            // start code……
        }else{
            if(zsl.empty(grey_img_icon)){
                grey_img(path,function(imgObj){
                    // 设置灰色图标
                    chrome.browserAction.setIcon({
                        imageData: imgObj.ctx.getImageData(0,0,128,128)
                    });
                })
            }
            
            // 关闭程序
            // close code……
        }
    }
}