你在画布上画的任何东西 - 像圆圈,就像画布上的油漆一样。
您的圈子无法像html元素一样被选中或移动。
要移动圆圈,您必须清除画布并在不同位置重绘圆圈。
在对象中存储有关圆的信息很方便。
var circle1 = { centerX:100, centerY=100, radius=20 }
,你能画CIRCLE1使用信息:
ctx.beginPath();
ctx.arc(circle1.centerX, circle1.centerY, circle1.radius, 0,Math.PI*2);
ctx.closePath();
ctx.fill();
在超过1圈,你可以创建一个圆阵,并把每一个圆圈对象成数组
var circles=[];
circles.push(circle1);
然后要“移动”一个圆圈,只需将对象的centerX/centerY更改为鼠标位置,然后重画画布上的所有圆。
circle1.centerX=mouseX;
circle1.centerY=mouseY;
// Clear the canvas and redraw all circles
// The "moved" circle will be redrawn at its new position
function drawAll(){
ctx.clearRect(0,0,canvas.width,canvas.height);
for(var i=0;i<circles.length;i++){
var c=circles[i];
ctx.beginPath();
ctx.arc(c.centerX,c.centerY,c.radius,0,Math.PI*2);
ctx.closePath();
ctx.fillStyle=c.color;
ctx.fill();
}
}
您可以使用HTML单选按钮来确定一个鼠标点击会做哪些动作:
- 创建在鼠标位置的新圈子,或
- 选择鼠标的位置下面的圆圈或
- “移动”当前选定的圆
这里的示例代码和一个演示:http://jsfiddle.net/m1erickson/CEB7T/
<!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(){
// get references to the canvas and its context
var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
var $canvas=$("#canvas");
// get the canvas position on the page
// used to get mouse position
var canvasOffset=$canvas.offset();
var offsetX=canvasOffset.left;
var offsetY=canvasOffset.top;
var scrollX=$canvas.scrollLeft();
var scrollY=$canvas.scrollTop();
ctx.lineWidth=3;
// save info about each circle in an object
var circles=[];
var selectedCircle=-1;
// the html radio buttons indicating what action to do upon mousedown
var $create=$("#rCreate")[0];
var $select=$("#rSelect")[0];
var $move=$("#rMove")[0];
// draw all circles[]
function drawAll(){
ctx.clearRect(0,0,canvas.width,canvas.height);
for(var i=0;i<circles.length;i++){
var c=circles[i];
ctx.beginPath();
ctx.arc(c.cx,c.cy,c.radius,0,Math.PI*2);
ctx.closePath();
ctx.fillStyle=c.color;
ctx.fill();
// if this is the selected circle, highlight it
if(selectedCircle==i){
ctx.strokeStyle="red";
ctx.stroke();
}
}
}
function handleMouseDown(e){
e.preventDefault();
mouseX=parseInt(e.clientX-offsetX);
mouseY=parseInt(e.clientY-offsetY);
if($create.checked){
// create a new circle a the mouse position and select it
circles.push({cx:mouseX,cy:mouseY,radius:10,color:randomColor()});
selectedCircle=circles.length-1;
}
if($select.checked){
// unselect any selected circle
selectedCircle=-1;
// iterate circles[] and select a circle under the mouse
for(var i=0;i<circles.length;i++){
var c=circles[i];
var dx=mouseX-c.cx;
var dy=mouseY-c.cy;
var rr=c.radius*c.radius;
if(dx*dx+dy*dy<rr){ selectedCircle=i; }
}
}
if($move.checked && selectedCircle>=0){
// move the selected circle to the mouse position
var c=circles[selectedCircle];
c.cx=mouseX;
c.cy=mouseY;
}
// redraw all circles
drawAll();
}
// return a random color
function randomColor(){
return('#'+Math.floor(Math.random()*16777215).toString(16));
}
// handle mousedown events
$("#canvas").mousedown(function(e){handleMouseDown(e);});
}); // end $(function(){});
</script>
</head>
<body>
<input type="radio" name="grp1" id="rCreate" checked>Click will create a new circle.<br>
<input type="radio" name="grp1" id="rSelect">Click will select an existing circle.<br>
<input type="radio" name="grp1" id="rMove">Click will move selected circle.<br>
<canvas id="canvas" width=300 height=300></canvas>
</body>
</html>