canvas笔记-在canvas中使用其他HTML元素

这里使用的原理是使用css把div中关于html的元素通过布局位置，以及透明相关的设置，将其设置到canvas上，这样看起来就是在canvas绘制的按钮。然后使用JavaScript获取按钮的数据或者其他数据设置到canvas中。

程序运行截图如下：

点击控制面板的按钮

再点击一个

源码如下：

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>

    <style>
        #canvas-wrapper{
            width: 1200px;
            height: 800px;
            position: relative;
            margin: 50px auto;
        }
        #canvas{
            border: 1px solid #aaaaaa;
        }
        #controller{
            position: absolute;
            top: 30px;
            left: 30px;
            background-color: rgba(0, 85, 116, 0.7);
            padding: 5px 20px 25px 20px;
            border-radius: 10px 10px;
        }
        #controller h1{
            color: white;
            font-width: bold;
            font-family: Microsoft Yahei;
        }
        #controller .color-btn{

            display: inline-block;
            padding: 5px 15px;
            border-radius: 6px 6px;
            font-size: 14px;
            margin-top: 10px;
            margin-right: 5px;
            text-decoration: none;
        }

        #controller #white-color-btn{

            background-color: white;
        }

        #controller #black-color-btn{

            background-color: black;
        }

        #controller #green-color-btn{

            background-color: green;
        }

        #controller #blue-color-btn{

            background-color: blue;
        }
    </style>

</head>
<body>

<div id="canvas-wrapper">
    <canvas id="canvas" style="border: 1px solid #aaa; display: block; margin: 50px auto;">
        当前浏览器不支持canvas
    </canvas>
    <div id="controller">
        <h1>控制面板</h1>
        <a href="#" class="color-btn" id="white-color-btn">&nbsp</a>
        <a href="#" class="color-btn" id="black-color-btn">&nbsp</a>
        <a href="#" class="color-btn" id="green-color-btn">&nbsp</a>
        <a href="#" class="color-btn" id="blue-color-btn">&nbsp</a>
    </div>
</div>

<script>

    window.onload = function(){

        let canvas = document.getElementById("canvas");
        canvas.width = 1200;
        canvas.height = 800;
        let context = canvas.getContext("2d");

        document.getElementById("white-color-btn").onclick = function(event){

            context.clearRect(0, 0, canvas.width, canvas.height);
            context.fillStyle = "white";
            context.fillRect(0, 0, canvas.width, canvas.height);
            return false;
        }

        document.getElementById("black-color-btn").onclick = function(event){

            context.clearRect(0, 0, canvas.width, canvas.height);
            context.fillStyle = "black";
            context.fillRect(0, 0, canvas.width, canvas.height);
            return false;
        }

        document.getElementById("green-color-btn").onclick = function(event){

            context.clearRect(0, 0, canvas.width, canvas.height);
            context.fillStyle = "green";
            context.fillRect(0, 0, canvas.width, canvas.height);
            return false;
        }

        document.getElementById("blue-color-btn").onclick = function(event){

            context.clearRect(0, 0, canvas.width, canvas.height);
            context.fillStyle = "blue";
            context.fillRect(0, 0, canvas.width, canvas.height);
            return false;
        }
    }
    
</script>

</body>
</html>

这里解析下上面代码的部分逻辑，这里把canvas和按钮相关都放到id为canvas-wrapper的div中，在canvas-wrapper中的css使用position为relative也就是相对定位的元素。在id为controller中div中将position设置为absolute，也就是生成绝对定位的元素，然后设置下透明度啥的。

canvas笔记-在canvas中使用其他HTML元素

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