Canvas实现画板

Rinsann 2021年08月11日 371次浏览

Canvas

在使用Canvas实现画板手机版时,需要检测是否支持触屏,找到了以下代码

var isTouchDevice = 'ontouchstart' in document.documentElement;
console.log(isTouchDevice)

还可以这样写

function isTouchDevice() {
    return (('ontouchstart' in window) ||
    (navigator.maxTouchPoints > 0) ||
    (navigator.msMaxTouchPoints > 0));
}

Canvas画板代码

<!DOCTYPE html>
<html lang="zh-CN">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>画板</title>
    <link rel="stylesheet" href="style.css">
</head>
<body>
    <canvas id="canvas" width="100" height="100"></canvas>
    <script>
        let canvas = document.getElementById("canvas");
        canvas.width = document.documentElement.clientWidth
        canvas.height = document.documentElement.clientHeight
        let ctx = canvas.getContext("2d");
        ctx.fillStyle = "black";
        ctx.strokeStyle = 'none';
        ctx.lineWidth = 8;
        ctx.lineCap = "round";

        
        let painting = false
        let last

        var isTouchDevice = 'ontouchstart' in document.documentElement;
        
        if(isTouchDevice){
            canvas.ontouchstart  = (e) => {
                let x = e.touches[0].clientX
                let y = e.touches[0].clientY
                last = [x,y]
            }
            canvas.ontouchmove  = (e) => {
                let x = e.touches[0].clientX
                let y = e.touches[0].clientY
                drawLine(last[0],last[1],x,y)
                last = [x,y]
            }
        }else{
            canvas.onmousedown = (e) => {
                painting = true
                last = [e.clientX,e.clientY]
            }
            
            canvas.onmousemove = (e) => {

                if(painting === true){
                    drawLine(last[0],last[1],e.clientX,e.clientY)
                    last = [e.clientX,e.clientY]
                }
            }
            
            canvas.onmouseup = () => {
                painting = false
            }
        }
        
        function drawLine(x1,y1,x2,y2){
            ctx.beginPath();
            ctx.moveTo(x1, y1);
            ctx.lineTo(x2, y2);
            ctx.stroke();
        }
        
        </script>
</body>
</html>
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

#canvas {
  display: block;
}