Canvas实现圆角图片实例页面

HTML代码：

<strong>这是原图</strong>
<p><img src="//image.zhangxinxu.com/image/study/s/s256/mm1.jpg" width="256" height="191"></p>
<strong>这是Canvas实现</strong>
<p>圆角大小：<span class="range-txt"> 0 <input id="radiusInput" type="range" min="0" max="92" value="92"> 92</span></p>
<canvas id="canvas" width="256" height="191"></canvas>
                

JS代码：

//圆角矩形
CanvasRenderingContext2D.prototype.roundRect = function (x, y, w, h, r) {
    var min_size = Math.min(w, h);
    if (r > min_size / 2) r = min_size / 2;
    // 开始绘制
    this.beginPath();
    this.moveTo(x + r, y);
    this.arcTo(x + w, y, x + w, y + h, r);
    this.arcTo(x + w, y + h, x, y + h, r);
    this.arcTo(x, y + h, x, y, r);
    this.arcTo(x, y, x + w, y, r);
    this.closePath();
    return this;
}

// canvas元素, 图片元素
var canvas = document.querySelector("#canvas"), image = new Image(), input = document.getElementById("radiusInput");
var context = canvas.getContext("2d");

var draw = function(obj) {
    // 创建图片纹理
    var pattern = context.createPattern(obj, "no-repeat");
    // 如果要绘制一个圆，使用下面代码
    // context.arc(obj.width / 2, obj.height / 2, Math.max(obj.width, obj.height) / 2, 0, 2 * Math.PI);
    // 这里使用圆角矩形
    context.roundRect(0, 0, obj.width, obj.height, input.value * 1 || 0);
    
    // 填充绘制的圆
    context.fillStyle = pattern;
    context.fill();    
}

image.onload = function() {
    draw(this);
};
image.src = "//image.zhangxinxu.com/image/study/s/s256/mm1.jpg";

input.addEventListener("change", function() {
    context.clearRect(0, 0, canvas.width, canvas.height);
    draw(image);	
});