runsly Html5教程 2021-12-14

html5实现一个简单的在线画板

我们先来看看实现效果：

（推荐教程：h5）

实现代码如下：

<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title></title>
    </head>
    <body>
        <canvas id="canvas" width="600" height="600"></canvas>
        <script type="text/javascript">
            var c = document.getElementById('canvas');
            var ctx = c.getContext('2d');

            //画一个黑色矩形
            ctx.fillStyle = 'black';
            ctx.fillRect(0,0,600,300);

            //按下标记
            var onoff = false;
            var oldx = -10;
            var oldy = -10;

            //设置颜色
            var linecolor = 'white';

            //设置线宽
            var linw = 4;

            //添加鼠标移动事件
            canvas.addEventListener('mousemove',draw,true);

            //添加鼠标按下事件
            canvas.addEventListener('mousedown',down,false);

            //添加鼠标弹起事件
            canvas.addEventListener('mouseup',up,false);

            function down(event) {
                onoff = true;
                oldx = event.pageX-10;
                oldy = event.pagey-10;
            }

            function up() {
                onoff = false;
            }

            function draw(event) {
                if(onoff == true) {
                    var newx = event.pageX-10;
                    var newy = event.pageY-10;
                    ctx.beginPath();
                    ctx.moveTo(oldx,oldy);
                    ctx.lineTo(newx,newy);
                    ctx.strokeStyle = linecolor;
                    ctx.lineCap = 'round';
                    ctx.stroke();

                    oldx = newx;
                    oldy = newy;
                }
            }
        </script>
    </body>
</html>

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html5 画板