这是以前写的涂鸦板一样的东西,按住鼠标左键拖拽就可以绘制指针的运动轨迹
<body>
<center>
<canvas id="cavsElem" width="800" height="560" style="border: 1px solid black; ">你的浏览器不支持此涂鸦板</canvas>
画笔颜色：<input type="color" id="context.color" />
画笔大小:<input type="number"id="context.size" max="10" value="1" />
</center>
<script>
(function(){
var canvas=document.getElementById('cavsElem');//获得画布
var context=canvas.getContext('2d');//准备画笔
var a=document.getElementById('context.color');
var b=document.getElementById('context.size');
canvas.onmousedown=function(e){ //鼠标触发onmousedown事件时,获取起始坐标
var x=e.clientX-canvas.getBoundingClientRect().left;
var y=e.clientY-canvas.getBoundingClientRect().top;
context.beginPath();
context.moveTo(x,y);
canvas.onmousemove=function(event){ //触发鼠标移动事件时，获取绘制线条的坐标
var x=event.clientX-canvas.getBoundingClientRect().left;
var y=event.clientY-canvas.getBoundingClientRect().top;
context.lineTo(x,y);//绘制线条
context.strokeStyle=a.value;
context.lineWidth=b.value;
context.stroke();
};
canvas.onmouseup=function(event){ //鼠标被松开时，返回null
canvas.onmousemove=null;
};
};
}());
</script>
</body>
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