Canvas入门笔记-实现极简画笔

1 <div>
2     <!--画板-->
3     <canvas id="box1" height="400" width="400" style="background-color: antiquewhite"></canvas>
4     <!--保存并显示鼠标X轴位置-->
5     <label id="lab_X"></label>
6     <!--保存并显示鼠标Y轴位置-->
7     <label id="lab_Y"></label>
8 </div>

 1 $(function () {
 2             var canvas = document.getElementById("box1");
 3             if (canvas == null)
 4                 return false;
 5             var context = canvas.getContext("2d");
 6             //标记开始书写
 7             var start = false;
 8             $(canvas).mousemove(function (event) {
 9                 //显示当前鼠标位置
10                 $("#lab_X").text(event.pageX);
11                 $("#lab_Y").text(event.pageY);
12                 if (start) {
13                     context.lineTo(event.pageX, event.pageY);
14                     context.stroke();
15                 }
16             });
17             //鼠标按下，开始书写
18             $(canvas).mousedown(function () {
19                 context.beginPath();
20                 context.moveTo($("#lab_X").text(), $("#lab_Y").text());
21                 start = true;
22             });
23             //鼠标抬起，结束书写
24             $(canvas).mouseup(function () {
25 
26                 start = false;
27                 context.closePath();
28             });
29         });