HTML5 Cavans(8) 图像

$代表jquery

        window.onload = function () {
            var cancans = document.getElementById("myCanvas");
            //得到2D渲染上下文
            var context = document.getElementById("myCanvas").getContext("2d");

            var img = new Image();
            img.width = "500";
            img.height = "400";
            img.src = "images/canvas.png";
            $(img).load(function () {

                //context.drawImage(img, 0, 0); //默认图片大小
                //context.drawImage(img, 10, 10, 100, 100)//指定大小
                context.shadowBlur = 20;
                context.shadowColor = "blue";
                //图片裁剪 
                //参数 源图，源图原点x,y坐标，源图在原点开始的宽长,画布开始画的点x,y,宽长
                //drawImage(image, sx, sy, sw, sh, dx, dy, dw, dh);

                //万花筒效果
                //右下
                context.translate(200, 200);
                context.drawImage(img, 0, 0, 500, 500, 0, 0, 200, 200);

                //左下
                //先缩放，画布坐标已经改变，(-200,200)为原(200,200)位置
                context.setTransform(1, 0, 0, 1, 0, 0);
                context.scale(-1, 1);
                context.translate(-200, 200);
                context.drawImage(img, 0, 0, 500, 500, 0, 0, 200, 200);

                //左上
                //先定位，不需要重新转换位置
                context.setTransform(1, 0, 0, 1, 0, 0);
                context.translate(200, 200);
                context.scale(-1, -1);
                context.drawImage(img, 0, 0, 500, 500, 0, 0, 200, 200);

                //右上
                context.setTransform(1, 0, 0, 1, 0, 0);
                context.translate(200, 200);
                context.scale(1, -1);
                context.drawImage(img, 0, 0, 500, 500, 0, 0, 200, 200);

            });

        };