本文介绍在 HTML5 Canvas 中删除指定矩形区域的方法。通过调用 clearRect 函数，可以清除画布上特定坐标和尺寸的像素区域。示例代码展示了如何在 Canvas 中绘制矩形并清除其中一部分，适用于需要局部擦除或透明化处理的场景。
Canvas 删除矩形区域方法概述
本文介绍在 HTML5 Canvas 中删除指定矩形区域的方法，供读者参考。
运行效果截图如下：
附注：图中黑色小方块即为被删除的矩形区域。
具体实现代码如下：
index.html 文件内容如下：
HTML 结构实现
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-type" content="text/html;charset=UTF-8" />
<title>canvas中删除一块区域</title>
<style type="text/css">
#canvas {
background:black; margin-top:100px; margin-left:200px;
}
</style>
</head>
<body>
<canvas id="canvas" width="500px" height="500px" ></canvas>
</body>
<script type="text/javascript" src="canvas.js"></script>
<script type="text/javascript">
cache = {};
var offsetX = 50,
offsetY = 20;
cache.context = dyl.createContext('canvas');
dyl.rect(dyl.createColor(), 150, 150, 200, 200, 0.5);
for(var i=0; i<10; i++) {
dyl.clearRect(150 + i*20, 150 + i*20, 20, 20);
}
</script>
</html>
canvas.js 文件内容如下：
JavaScript 逻辑实现
(function() {
var dyl = {cache: {}};
dyl.setContext = function(context) {
dyl.cache._context = context;
return context;
};
dyl.getDom = function(id) {
return document.getElementById(id);
};
dyl._getContext = function() {
return dyl.cache._context;
};
dyl.save = function() {
var context = dyl._getContext();
context ? context.save() : void(0);
};
dyl.restore = function() {
var context = dyl._getContext();
context ? context.restore() : void(0);
};
dyl.createContext = function(canvasID) {
var canvas = this.getDom(canvasID);
if(!canvas) {
return null;
}
return dyl.setContext(canvas.getContext("2d"));
};
dyl.createColor = function() {
var color = "rgb(";
color += Math.round(Math.random()*255);
color += ",";
color += Math.round(Math.random()*255);
color += ",";
color += Math.round(Math.random()*255);
color += ")";
return color;
};
dyl.addImg = function(img, x, y) {
var context = dyl._getContext();
if(!img || !context) {
return;
}
if(typeof img === "string") {
var oImg = new Image();
oImg.src = img;
oImg.onload = function() {
context.drawImage(oImg, x, y);
}
return;
}
context.drawImage(img, x, y);
};
dyl.rect = function(color, x, y, width, height, alpha) {
var context = dyl._getContext();
if(!context) {
return;
}
context.save();
context.fillStyle = color;
context.globalAlpha = alpha ? alpha : 1;
context.fillRect(x, y, width, height);
context.restore();
};
dyl.circle = function(color, x, y, r, alpha) {
var context = dyl._getContext();
context.save();
context.fillStyle = color;
context.beginPath();
context.globalAlpha = alpha ? alpha : 1;
context.arc(x, y, r, 0, 2*Math.PI);
context.fill();
context.stroke();
};
dyl.clearRect = function(x, y, width, height) {
var context = dyl._getContext();
if(!context) {
return;
}
context.clearRect(x, y, width, height);
};
dyl.scale = function(x, y) {
var context = dyl._getContext();
if(!context) {
return;
}
x = x ? x : 1;
y = y ? y : 1;
context.scale(x, y);
};
if(!window.dyl) {
window.dyl = dyl;
}
})();
希望本文所述内容对 JavaScript 程序设计有所帮助。