<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>canvas制作圆角矩形（包括填充矩形的功能）</title>
</head>
<body>
<canvas id="myCanvas" style="border:1px solid #d3d3d3;">
您的浏览器不支持 HTML5 canvas 标签。</canvas>
<script>
window.onload = function() {
var myCanvas = document.getElementById("myCanvas"); //获取canvas对象
if (myCanvas.getContext("2d")) { //判断浏览器是否支持canvas标签
//设置canvas的宽度和高度
myCanvas.width = 400;
myCanvas.height = 200;
var context = myCanvas.getContext("2d"); //获取画布context的上下文环境
//绘制一个圆角矩形
strokeRoundRect(context, 10, 10, 100, 50, 10);
//绘制并填充一个圆角矩形
fillRoundRect(context, 200, 10, 100, 50, 10, 'rgba(0,0,0,0.7)');
} else {
alert("您的浏览器不支持canvas，请换个浏览器试试");
}
};
/**该方法用来绘制一个有填充色的圆角矩形
*@param cxt:canvas的上下文环境
*@param x:左上角x轴坐标
*@param y:左上角y轴坐标
*@param width:矩形的宽度
*@param height:矩形的高度
*@param radius:圆的半径
*@param fillColor:填充颜色
**/
function fillRoundRect(cxt, x, y, width, height, radius, /*optional*/ fillColor) {
//圆的直径必然要小于矩形的宽高
if (2 * radius > width || 2 * radius > height) { return false; }
cxt.save();
cxt.translate(x, y);
//绘制圆角矩形的各个边
drawRoundRectPath(cxt, width, height, radius);
cxt.fillStyle = fillColor || "#000"; //若是给定了值就用给定的值否则给予默认值
cxt.fill();
cxt.restore();
}
/**该方法用来绘制圆角矩形
*@param cxt:canvas的上下文环境
*@param x:左上角x轴坐标
*@param y:左上角y轴坐标
*@param width:矩形的宽度
*@param height:矩形的高度
*@param radius:圆的半径
*@param lineWidth:线条粗细
*@param strokeColor:线条颜色
**/
function strokeRoundRect(cxt, x, y, width, height, radius, /*optional*/ lineWidth, /*optional*/ strokeColor) {
//圆的直径必然要小于矩形的宽高
if (2 * radius > width || 2 * radius > height) { return false; }
cxt.save();
cxt.translate(x, y);
//绘制圆角矩形的各个边
drawRoundRectPath(cxt, width, height, radius);
cxt.lineWidth = lineWidth || 2; //若是给定了值就用给定的值否则给予默认值2
cxt.strokeStyle = strokeColor || "#000";
cxt.stroke();
cxt.restore();
}
function drawRoundRectPath(cxt, width, height, radius) {
cxt.beginPath(0);
//从右下角顺时针绘制，弧度从0到1/2PI
cxt.arc(width - radius, height - radius, radius, 0, Math.PI / 2);
//矩形下边线
cxt.lineTo(radius, height);
//左下角圆弧，弧度从1/2PI到PI
cxt.arc(radius, height - radius, radius, Math.PI / 2, Math.PI);
//矩形左边线
cxt.lineTo(0, radius);
//左上角圆弧，弧度从PI到3/2PI
cxt.arc(radius, radius, radius, Math.PI, Math.PI * 3 / 2);
//上边线
cxt.lineTo(width - radius, 0);
//右上角圆弧
cxt.arc(width - radius, radius, radius, Math.PI * 3 / 2, Math.PI * 2);
//右边线
cxt.lineTo(width, height - radius);
cxt.closePath();
}
</script>
</body>
</html>
