canvas日常操作

/**
     * Canvas 转 base64
     * @param canvas：canvas元素
     * @param backgroundColor：背景色
     **/
    canvasToImage:function (canvas,backgroundColor) {
        var w = canvas.width;
        var h = canvas.height;
        var context = canvas.getContext("2d");
        var data;
        if(backgroundColor) {
            //get the current ImageData for the canvas.
            data = context.getImageData(0, 0, w, h);

            //store the current globalCompositeOperation
            var compositeOperation = context.globalCompositeOperation;

            //set to draw behind current content
            context.globalCompositeOperation = "destination-over";

            //set background color
            context.fillStyle = backgroundColor;

            //draw background / rect on entire canvas
            context.fillRect(0,0,w,h);
        }

        //get the image data from the canvas
        var imageData = canvas.toDataURL("image/png");

        if(backgroundColor){
            //clear the canvas
            context.clearRect (0,0,w,h);

            //restore it with original / cached ImageData
            context.putImageData(data, 0,0);

            //reset the globalCompositeOperation to what it was
            context.globalCompositeOperation = compositeOperation;
        }

        //return the Base64 encoded data url string
        return imageData;
    },

//Echarts 转 base64
var baseCanvas = $("#container").find("canvas").first()[0];//获取原生的canvas
var base64Img = TMS.canvasToImage(baseCanvas,‘#fff‘); //获得base64