用鼠标移动画布形状
[英]Moving canvas shapes with mouse
问题描述
After pressing a button, I'd like to draw a circle at the tip of the mouse pointer on a canvas and then place it when the user clicks again. 
按下按钮后，我想在画布上鼠标指针的尖端绘制一个圆圈，然后在用户再次单击时将其放置。 Here's what I've got so far: 到目前为止，这是我得到的：
$("#button").click(function(e){
var canvas = document.getElementById('MyCanvas');
var context = canvas.getContext('2d');
canvas.addEventListener('mousemove', function(evt) {
var mousePos = getMousePos(canvas, evt);
var message = 'Mouse position: ' + mousePos.x + ',' + mousePos.y;
console.log(message);
var nodehandle = document.getElementById('circle');
if(mousePos.x && mousePos.y) {
nodehandle.x = mousePos.x;
nodehandle.y = mousePos.y;
flag = 1;
}
}, false);
});
function getMousePos(canvas, evt) {
var rect = canvas.getBoundingClientRect();
return {
x: evt.clientX - rect.left,
y: evt.clientY - rect.top
};
}
My problem is that when I draw a circle like this: 我的问题是当我画一个圆形时：
function drawCircle(mouseX, mouseY){
var c = document.getElementById("grid");
var ctx = c.getContext("2d");
ctx.beginPath();
ctx.arc(95,50,5,0,2*Math.PI);
ctx.stroke();
}
I don't know how to select that circle (the getElementById('circle') returns null even if I add ctx.id='circle' to the drawCircle function). 我不知道如何选择该圆（即使我将ctx.id ='circle'添加到drawCircle函数中，getElementById（'circle'）也会返回null）。 I'm also going to need to erase and redraw the circle each time the mouse moves, and I'm sure there's a nice way to do that but I'm not aware of it. 每当鼠标移动时，我还需要擦除并重画圆圈，我敢肯定有一种不错的方法，但我不知道。
1 个解决方案
解决方案1
2 2014-03-03 05:13:32
Anything you draw on the canvas--like circles, are just like dried paint on the canvas. 您在画布上绘制的所有内容（例如圆圈）都像画布上的干漆一样。
Your circles cannot be selected or moved like html elements. 您的圈子无法像html元素一样选择或移动。
To move a circle you must clear the canvas and redraw the circle at a different location. 要移动圆，必须清除画布，然后在其他位置重新绘制圆。
It's convenient to store info about the circle in an object. 将有关圆的信息存储在对象中很方便。
var circle1 = { centerX:100, centerY=100, radius=20 }
And you can draw circle1 using that info: 您可以使用该信息绘制circle1：
ctx.beginPath();
ctx.arc(circle1.centerX, circle1.centerY, circle1.radius, 0,Math.PI*2);
ctx.closePath();
ctx.fill();
For more than 1 circle you can create a circles array and put each circle object into that array 对于一个以上的圆形，您可以创建一个圆形数组并将每个圆形对象放入该数组中
var circles=[];
circles.push(circle1);
Then to "move" a circle, just change the object's centerX/centerY to the mouse position and redraw all the circles on the canvas. 然后要“移动”一个圆，只需将对象的centerX / centerY更改为鼠标位置，然后在画布上重新绘制所有圆。
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();
}
}
You can use Html radio buttons to determine which action a mouse-click will do: 您可以使用HTML单选按钮来确定鼠标单击将执行的操作：
- Create a new circle at the mouse position, or 在鼠标位置创建一个新圆，或者
- Select the circle under the mouse position, or 选择鼠标位置下方的圆圈，或
- "Move" the currently selected circle “移动”当前选定的圈子
Here's example code and a Demo: http://jsfiddle.net/m1erickson/CEB7T/ 这是示例代码和演示： 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>
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