Demo: http://jsfiddle.net/m1erickson/7vmML/ http://jsfiddle.net/m1erickson/7vmML/
示例代码：
<!doctype html>
<html>
<head>
<link rel="stylesheet" type="text/css" media="all" href="css/reset.css" /> <!-- reset css -->
<script type="text/javascript" src="http://code.jquery.com/jquery.min.js"></script>
<style>
body{ background-color: ivory; }
#canvas{border:1px solid red;}
</style>
<script>
$(function(){
var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
var $canvas=$("#canvas");
var canvasOffset=$canvas.offset();
var offsetX=canvasOffset.left;
var offsetY=canvasOffset.top;
var scrollX=$canvas.scrollLeft();
var scrollY=$canvas.scrollTop();
var isDown=false;
var startX;
var startY;
var points=[];
points.push({x:10,y:10});
points.push({x:75,y:100});
points.push({x:150,y:125});
points.push({x:125,y:200});
var imageX=-200;
var imageY=-200;
var img=new Image();
img.onload=start;
img.crossOrigin="anonymous";
img.src="https://dl.dropboxusercontent.com/u/139992952/stackoverflow/house32x32transparent.png";
function start(){
drawAll();
}
function drawAll(){
ctx.clearRect(0,0,canvas.width,canvas.height);
ctx.beginPath();
ctx.moveTo(points[0].x+4,points[0].y+4)
for(var i=1;i<points.length;i++){
var pt=points[i];
ctx.lineTo(pt.x+4,pt.y+4);
}
ctx.stroke();
//
for(var i=0;i<points.length;i++){
var pt=points[i];
ctx.fillRect(pt.x,pt.y,8,8);
}
//
ctx.drawImage(img,imageX,imageY);
}
function handleMouseDown(e){
e.preventDefault();
isDown=true;
}
function handleMouseUp(e){
e.preventDefault();
isDown=false;
}
function handleMouseOut(e){
e.preventDefault();
isDown=false;
}
function handleMouseMove(e){
if(!isDown){return;}
e.preventDefault();
mouseX=parseInt(e.clientX-offsetX);
mouseY=parseInt(e.clientY-offsetY);
var minDistance=1000;
var minPoint=-1;
for(var i=0;i<points.length;i++){
var pt=points[i];
var dx=mouseX-pt.x;
var dy=mouseY-pt.y;
var distance=Math.sqrt(dx*dx+dy*dy);
if(distance<minDistance){
minDistance=distance;
imageX=pt.x-img.width/2;
imageY=pt.y-img.height/2;
}
}
drawAll();
}
$("#canvas").mousedown(function(e){handleMouseDown(e);});
$("#canvas").mousemove(function(e){handleMouseMove(e);});
$("#canvas").mouseup(function(e){handleMouseUp(e);});
$("#canvas").mouseout(function(e){handleMouseOut(e);});
}); // end $(function(){});
</script>
</head>
<body>
<h4>Drag mouse. Image will snap to nearest point.</h4>
<canvas id="canvas" width=300 height=300></canvas>
</body>
</html>
请注意，此示例代码使用 jQuery 来侦听鼠标事件。如果您更喜欢纯 JavaScript，则可以使用这些事件绑定：
canvas.onmousedown=handleMouseDown;
canvas.onmouseup=handleMouseUp;
canvas.onmouseout=handleMouseOut;
canvas.onmousemove=handleMouseMove;
你可以这样计算鼠标位置：
function getMousePos(canvas,e) {
var rect=canvas.getBoundingClientRect();
return{ x:e.clientX-rect.left, y:e.clientY-rect.top };
}
