使用鼠标在 HTML5 Canvas 上绘图
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【中文标题】使用鼠标在 HTML5 Canvas 上绘图【英文标题】：Draw on HTML5 Canvas using a mouse 【发布时间】：2011-01-23 01:13:26 【问题描述】：我想用鼠标在 html Canvas 上绘图（例如，画签名、画名字……）
我将如何实施？
【问题讨论】：
检查这个！ ***.com/questions/3814442/… 相关javascript library for free form drawing 另见：How do I hand draw on canvas? 好问题。谢谢 【参考方案1】：这是一个工作示例。
<html>
<script type="text/javascript">
var canvas, ctx, flag = false,
prevX = 0,
currX = 0,
prevY = 0,
currY = 0,
dot_flag = false;
var x = "black",
y = 2;
function init()
canvas = document.getElementById('can');
ctx = canvas.getContext("2d");
w = canvas.width;
h = canvas.height;
canvas.addEventListener("mousemove", function (e)
findxy('move', e)
, false);
canvas.addEventListener("mousedown", function (e)
findxy('down', e)
, false);
canvas.addEventListener("mouseup", function (e)
findxy('up', e)
, false);
canvas.addEventListener("mouseout", function (e)
findxy('out', e)
, false);
function color(obj)
switch (obj.id)
case "green":
x = "green";
break;
case "blue":
x = "blue";
break;
case "red":
x = "red";
break;
case "yellow":
x = "yellow";
break;
case "orange":
x = "orange";
break;
case "black":
x = "black";
break;
case "white":
x = "white";
break;
if (x == "white") y = 14;
else y = 2;
function draw()
ctx.beginPath();
ctx.moveTo(prevX, prevY);
ctx.lineTo(currX, currY);
ctx.strokeStyle = x;
ctx.lineWidth = y;
ctx.stroke();
ctx.closePath();
function erase()
var m = confirm("Want to clear");
if (m)
ctx.clearRect(0, 0, w, h);
document.getElementById("canvasimg").style.display = "none";
function save()
document.getElementById("canvasimg").style.border = "2px solid";
var dataURL = canvas.toDataURL();
document.getElementById("canvasimg").src = dataURL;
document.getElementById("canvasimg").style.display = "inline";
function findxy(res, e)
if (res == 'down')
prevX = currX;
prevY = currY;
currX = e.clientX - canvas.offsetLeft;
currY = e.clientY - canvas.offsetTop;
flag = true;
dot_flag = true;
if (dot_flag)
ctx.beginPath();
ctx.fillStyle = x;
ctx.fillRect(currX, currY, 2, 2);
ctx.closePath();
dot_flag = false;
if (res == 'up' || res == "out")
flag = false;
if (res == 'move')
if (flag)
prevX = currX;
prevY = currY;
currX = e.clientX - canvas.offsetLeft;
currY = e.clientY - canvas.offsetTop;
draw();
</script>
<body onload="init()">
<canvas id="can" style="position:absolute;top:10%;left:10%;border:2px solid;"></canvas>
<div style="position:absolute;top:12%;left:43%;">Choose Color</div>
<div style="position:absolute;top:15%;left:45%;width:10px;height:10px;background:green;" id="green" onclick="color(this)"></div>
<div style="position:absolute;top:15%;left:46%;width:10px;height:10px;background:blue;" id="blue" onclick="color(this)"></div>
<div style="position:absolute;top:15%;left:47%;width:10px;height:10px;background:red;" id="red" onclick="color(this)"></div>
<div style="position:absolute;top:17%;left:45%;width:10px;height:10px;background:yellow;" id="yellow" onclick="color(this)"></div>
<div style="position:absolute;top:17%;left:46%;width:10px;height:10px;background:orange;" id="orange" onclick="color(this)"></div>
<div style="position:absolute;top:17%;left:47%;width:10px;height:10px;background:black;" id="black" onclick="color(this)"></div>
<div style="position:absolute;top:20%;left:43%;">Eraser</div>
<div style="position:absolute;top:22%;left:45%;width:15px;height:15px;background:white;border:2px solid;" id="white" onclick="color(this)"></div>
<img id="canvasimg" style="position:absolute;top:10%;left:52%;" style="display:none;">
<input type="button" value="save" id="btn" size="30" onclick="save()" style="position:absolute;top:55%;left:10%;">
<input type="button" value="clear" id="clr" size="23" onclick="erase()" style="position:absolute;top:55%;left:15%;">
</body>
</html>【讨论】：
为什么要切换？你也可以做 x = obj.id。完成。 我正在尝试使用此代码，但是当我没有在页面上一直向下滚动时，绘图会垂直关闭。我应该在此代码中更改什么？ 我将canvas.offsetLeft; 和canvas.offsetTop; 分别更改为canvas.getBoundingClientRect().left; 和canvas.getBoundingClientRect().top; 以解决滚动问题。
这段代码让我走上了正确的道路。但我不得不说这段代码非常粗糙和丑陋。对于任何发现此问题并在鼠标位置上苦苦挣扎的人，请查看以下答案：***.com/a/17130415/5552144
要使其与绘图笔（如图形输入板）一起使用，必须将鼠标事件替换为触摸事件，例如。 touchmove、touchstart、touchend 然后clientX 来自e.touches["0"].clientX 代码中的findxy()，但还没有想到一种简单的方法来检测正在使用的内容，因为你听不到从我测试的结果来看，这两个事件同时发生。我按原样离开了mouseout。它并不完美，但确实有效【参考方案2】：
我想，这里的其他例子太复杂了。这个比较简单，只有JS...
// create canvas element and append it to document body
var canvas = document.createElement('canvas');
document.body.appendChild(canvas);
// some hotfixes... ( ≖_≖)
document.body.style.margin = 0;
canvas.style.position = 'fixed';
// get canvas 2D context and set him correct size
var ctx = canvas.getContext('2d');
resize();
// last known position
var pos = x: 0, y: 0 ;
window.addEventListener('resize', resize);
document.addEventListener('mousemove', draw);
document.addEventListener('mousedown', setPosition);
document.addEventListener('mouseenter', setPosition);
// new position from mouse event
function setPosition(e)
pos.x = e.clientX;
pos.y = e.clientY;
// resize canvas
function resize()
ctx.canvas.width = window.innerWidth;
ctx.canvas.height = window.innerHeight;
function draw(e)
// mouse left button must be pressed
if (e.buttons !== 1) return;
ctx.beginPath(); // begin
ctx.lineWidth = 5;
ctx.lineCap = 'round';
ctx.strokeStyle = '#c0392b';
ctx.moveTo(pos.x, pos.y); // from
setPosition(e);
ctx.lineTo(pos.x, pos.y); // to
ctx.stroke(); // draw it!
【讨论】：
@RyanCameron.Me 只需评论行if (e.buttons !== 1) return; ;-)。
@RyanCameron.Me 刚刚尝试了最新的 Chrome、Firefox 和 Edge，一切正常……你用什么浏览器？
@RyanCameron.Me 这更有可能是因为我的resize 函数。我正在根据窗口大小设置画布的宽度和高度。你应该根据你的<div class="container-fluid">来设置这些。
这有助于从设置位置函数的 y 坐标中减去大约 250。非常感谢您的帮助！
@TaylorA.Leach 是的，如果canvas没有放在右上角，你需要在setPosition函数中添加一些offset...【参考方案3】：
这是使用画布创建绘图应用程序的最直接方法：
-
将
mousedown、mousemove 和mouseup 事件监听器附加到画布DOM
在mousedown 上，获取鼠标坐标，然后使用moveTo() 方法定位绘图光标并使用beginPath() 方法开始新的绘图路径。
在mousemove 上，用lineTo() 连续向路径添加一个新点，并用stroke() 为最后一段着色。
在mouseup 上，设置一个标志以禁用绘图。
从那里，您可以添加各种其他功能，例如让用户能够选择线条粗细、颜色、笔触甚至图层。
【讨论】：
如果有beginPath，mouseup后应该有closePath吗？ @Timo 当你stroke() 时，它会自动关闭路径。【参考方案4】：
用谷歌搜索了这个（“html5 画布绘制程序”）。看起来像你需要的。
http://dev.opera.com/articles/view/html5-canvas-painting/
【讨论】：
这个例子确实展示了如何画一个圆。不过其他的还是不错的。知道如何画圆吗？【参考方案5】：检查此http://jsfiddle.net/ArtBIT/kneDX/。这应该会指引你朝着正确的方向前进
【讨论】：
完美。应该收到 chk。我需要一种在现有图像上制作简单填充矩形的方法。您的代码正是我需要的模板。 tyvm！【参考方案6】：我也想使用这种方法进行签名，我在http://codetheory.in/ 上找到了一个示例。
我已将以下代码添加到 jsfiddle
HTML：
<div id="sketch">
<canvas id="paint"></canvas>
</div>
Javascript：
(function()
var canvas = document.querySelector('#paint');
var ctx = canvas.getContext('2d');
var sketch = document.querySelector('#sketch');
var sketch_style = getComputedStyle(sketch);
canvas.width = parseInt(sketch_style.getPropertyValue('width'));
canvas.height = parseInt(sketch_style.getPropertyValue('height'));
var mouse = x: 0, y: 0;
var last_mouse = x: 0, y: 0;
/* Mouse Capturing Work */
canvas.addEventListener('mousemove', function(e)
last_mouse.x = mouse.x;
last_mouse.y = mouse.y;
mouse.x = e.pageX - this.offsetLeft;
mouse.y = e.pageY - this.offsetTop;
, false);
/* Drawing on Paint App */
ctx.lineWidth = 5;
ctx.lineJoin = 'round';
ctx.lineCap = 'round';
ctx.strokeStyle = 'blue';
canvas.addEventListener('mousedown', function(e)
canvas.addEventListener('mousemove', onPaint, false);
, false);
canvas.addEventListener('mouseup', function()
canvas.removeEventListener('mousemove', onPaint, false);
, false);
var onPaint = function()
ctx.beginPath();
ctx.moveTo(last_mouse.x, last_mouse.y);
ctx.lineTo(mouse.x, mouse.y);
ctx.closePath();
ctx.stroke();
;
());
【讨论】：
最好的部分是您可以通过右键单击不同的位置来绘制直线连接线。 :) 不适用于触摸屏。不是指平板电脑。我的意思是带有鼠标和触摸屏的 Windows 10 笔记本电脑。 我得到：未捕获的类型错误：无法在“窗口”上执行“getComputedStyle”：参数 1 不是“元素”类型。【参考方案7】：这是我非常简单的画布绘制和擦除。
https://jsfiddle.net/richardcwc/d2gxjdva/
//Canvas
var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
//Variables
var canvasx = $(canvas).offset().left;
var canvasy = $(canvas).offset().top;
var last_mousex = last_mousey = 0;
var mousex = mousey = 0;
var mousedown = false;
var tooltype = 'draw';
//Mousedown
$(canvas).on('mousedown', function(e)
last_mousex = mousex = parseInt(e.clientX-canvasx);
last_mousey = mousey = parseInt(e.clientY-canvasy);
mousedown = true;
);
//Mouseup
$(canvas).on('mouseup', function(e)
mousedown = false;
);
//Mousemove
$(canvas).on('mousemove', function(e)
mousex = parseInt(e.clientX-canvasx);
mousey = parseInt(e.clientY-canvasy);
if(mousedown)
ctx.beginPath();
if(tooltype=='draw')
ctx.globalCompositeOperation = 'source-over';
ctx.strokeStyle = 'black';
ctx.lineWidth = 3;
else
ctx.globalCompositeOperation = 'destination-out';
ctx.lineWidth = 10;
ctx.moveTo(last_mousex,last_mousey);
ctx.lineTo(mousex,mousey);
ctx.lineJoin = ctx.lineCap = 'round';
ctx.stroke();
last_mousex = mousex;
last_mousey = mousey;
//Output
$('#output').html('current: '+mousex+', '+mousey+'<br/>last: '+last_mousex+', '+last_mousey+'<br/>mousedown: '+mousedown);
);
//Use draw|erase
use_tool = function(tool)
tooltype = tool; //update
canvas
cursor: crosshair;
border: 1px solid #000000;
<canvas id="canvas" ></canvas>
<input type="button" value="draw" onclick="use_tool('draw');" />
<input type="button" value="erase" onclick="use_tool('erase');" />
<div id="output"></div>【讨论】：
【参考方案8】：我必须为这个主题提供一个简单的例子，所以我会在这里分享：
http://jsfiddle.net/Haelle/v6tfp2e1
class SignTool
constructor()
this.initVars()
this.initEvents()
initVars()
this.canvas = $('#canvas')[0]
this.ctx = this.canvas.getContext("2d")
this.isMouseClicked = false
this.isMouseInCanvas = false
this.prevX = 0
this.currX = 0
this.prevY = 0
this.currY = 0
initEvents()
$('#canvas').on("mousemove", (e) => this.onMouseMove(e))
$('#canvas').on("mousedown", (e) => this.onMouseDown(e))
$('#canvas').on("mouseup", () => this.onMouseUp())
$('#canvas').on("mouseout", () => this.onMouseOut())
$('#canvas').on("mouseenter", (e) => this.onMouseEnter(e))
onMouseDown(e)
this.isMouseClicked = true
this.updateCurrentPosition(e)
onMouseUp()
this.isMouseClicked = false
onMouseEnter(e)
this.isMouseInCanvas = true
this.updateCurrentPosition(e)
onMouseOut()
this.isMouseInCanvas = false
onMouseMove(e)
if (this.isMouseClicked && this.isMouseInCanvas)
this.updateCurrentPosition(e)
this.draw()
updateCurrentPosition(e)
this.prevX = this.currX
this.prevY = this.currY
this.currX = e.clientX - this.canvas.offsetLeft
this.currY = e.clientY - this.canvas.offsetTop
draw()
this.ctx.beginPath()
this.ctx.moveTo(this.prevX, this.prevY)
this.ctx.lineTo(this.currX, this.currY)
this.ctx.strokeStyle = "black"
this.ctx.lineWidth = 2
this.ctx.stroke()
this.ctx.closePath()
var canvas = new SignTool()canvas
position: absolute;
border: 2px solid;
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<canvas id="canvas" ></canvas>【讨论】：
【参考方案9】：这个问题被问到并得到回答已经有好几年了。
对于任何寻找简单绘图画布的人（例如，从用户/客户那里获取签名），我在这里发布当前接受的答案的更简化的 jquery 版本
$(document).ready(function()
var flag, dot_flag = false,
prevX, prevY, currX, currY = 0,
color = 'black', thickness = 2;
var $canvas = $('#canvas');
var ctx = $canvas[0].getContext('2d');
$canvas.on('mousemove mousedown mouseup mouseout', function(e)
prevX = currX;
prevY = currY;
currX = e.clientX - $canvas.offset().left;
currY = e.clientY - $canvas.offset().top;
if (e.type == 'mousedown')
flag = true;
if (e.type == 'mouseup' || e.type == 'mouseout')
flag = false;
if (e.type == 'mousemove')
if (flag)
ctx.beginPath();
ctx.moveTo(prevX, prevY);
ctx.lineTo(currX, currY);
ctx.strokeStyle = color;
ctx.lineWidth = thickness;
ctx.stroke();
ctx.closePath();
);
$('.canvas-clear').on('click', function(e)
c_width = $canvas.width();
c_height = $canvas.height();
ctx.clearRect(0, 0, c_width, c_height);
$('#canvasimg').hide();
);
);<html>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.0/jquery.min.js"></script>
<body>
<canvas id="canvas" style="position:absolute;top:10%;left:10%;border:2px solid;"></canvas>
<input type="button" value="Clear" class="canvas-clear" />
</body>
</html>【讨论】：
【参考方案10】：一个超短的版本，here，没有 position:absolute 的原生 JavaScript。主要思想是将画布的上下文移动到正确的坐标并画一条线。取消注释click 处理程序并在下面评论mousedown 和mousemove 处理程序以了解它是如何工作的。
<!DOCTYPE html>
<html>
<body>
<p style="margin: 50px">Just some padding in y direction</p>
<canvas id="myCanvas" style="background: #000; margin-left: 100px;">Your browser does not support the HTML5 canvas tag.</canvas>
<script>
const c = document.getElementById("myCanvas");
// c.addEventListener("click", penTool); // fires after mouse left btn is released
c.addEventListener("mousedown", setLastCoords); // fires before mouse left btn is released
c.addEventListener("mousemove", freeForm);
const ctx = c.getContext("2d");
function setLastCoords(e)
const x, y = c.getBoundingClientRect();
lastX = e.clientX - x;
lastY = e.clientY - y;
function freeForm(e)
if (e.buttons !== 1) return; // left button is not pushed yet
penTool(e);
function penTool(e)
const x, y = c.getBoundingClientRect();
const newX = e.clientX - x;
const newY = e.clientY - y;
ctx.beginPath();
ctx.lineWidth = 5;
ctx.moveTo(lastX, lastY);
ctx.lineTo(newX, newY);
ctx.strokeStyle = 'white';
ctx.stroke();
ctx.closePath();
lastX = newX;
lastY = newY;
let lastX = 0;
let lastY = 0;
</script>
</body>
</html>
【讨论】：
重要的是，不要在 CSS 中设置宽度和高度，因为它只会拉伸画布而不是调整其大小 - ***.com/a/8693791/1585523【参考方案11】：Alco 检查这个： 示例：https://github.com/williammalone/Simple-HTML5-Drawing-App
文档：http://www.williammalone.com/articles/create-html5-canvas-javascript-drawing-app/
本文档包括以下代码：-
HTML：
<canvas id="canvas" ></canvas>
JS：
context = document.getElementById('canvas').getContext("2d");
$('#canvas').mousedown(function(e)
var mouseX = e.pageX - this.offsetLeft;
var mouseY = e.pageY - this.offsetTop;
paint = true;
addClick(e.pageX - this.offsetLeft, e.pageY - this.offsetTop);
redraw();
);
$('#canvas').mouseup(function(e)
paint = false;
);
$('#canvas').mouseleave(function(e)
paint = false;
);
var clickX = new Array();
var clickY = new Array();
var clickDrag = new Array();
var paint;
function addClick(x, y, dragging)
clickX.push(x);
clickY.push(y);
clickDrag.push(dragging);
//Also redraw
function redraw()
context.clearRect(0, 0, context.canvas.width, context.canvas.height); // Clears the canvas
context.strokeStyle = "#df4b26";
context.lineJoin = "round";
context.lineWidth = 5;
for(var i=0; i < clickX.length; i++)
context.beginPath();
if(clickDrag[i] && i)
context.moveTo(clickX[i-1], clickY[i-1]);
else
context.moveTo(clickX[i]-1, clickY[i]);
context.lineTo(clickX[i], clickY[i]);
context.closePath();
context.stroke();
还有一个很棒的例子http://perfectionkills.com/exploring-canvas-drawing-techniques/
【讨论】：
【参考方案12】：我使用了 1083202 所做的，但删除了所有控件，并实施了 KWILLIAMS 建议的更改，使其对滚动不敏感。我还把画布做得很大，基本上在我的整个页面上 2000x1600 像素，除了边距。我确实删除了所有绘图工具和按钮，并使用“蓝色”作为唯一颜色。
我将 JS 代码放在一个名为 myJS.js 的单独文件中，并将其放在一个名为“JS”的文件夹中：
然后我用笔记本电脑上的手写笔在触控板上写字，女巫比用手指或鼠标更好地工作。
我使用它的文档是一种非正式的，供内部使用，但是在制作 pdf 文件之前能够在上面画一些笔触是很好的。
var canvas, ctx, flag = false,
prevX = 0,
currX = 0,
prevY = 0,
currY = 0,
dot_flag = false;
var x = "blue",
y = 3;
function init()
canvas = document.getElementById('can');
ctx = canvas.getContext("2d");
w = canvas.width;
h = canvas.height;
canvas.addEventListener("mousemove", function (e)
findxy('move', e)
, false);
canvas.addEventListener("mousedown", function (e)
findxy('down', e)
, false);
canvas.addEventListener("mouseup", function (e)
findxy('up', e)
, false);
canvas.addEventListener("mouseout", function (e)
findxy('out', e)
, false);
function draw()
ctx.beginPath();
ctx.moveTo(prevX, prevY);
ctx.lineTo(currX, currY);
ctx.strokeStyle = x;
ctx.lineWidth = y;
ctx.stroke();
ctx.closePath();
function findxy(res, e)
if (res == 'down')
prevX = currX;
prevY = currY;
currX = e.clientX - canvas.getBoundingClientRect().left;
currY = e.clientY - canvas.getBoundingClientRect().top;
flag = true;
dot_flag = true;
if (dot_flag)
ctx.beginPath();
ctx.fillStyle = x;
ctx.fillRect(currX, currY, 2, 2);
ctx.closePath();
dot_flag = false;
if (res == 'up' || res == "out")
flag = false;
if (res == 'move')
if (flag)
prevX = currX;
prevY = currY;
currX = e.clientX - canvas.getBoundingClientRect().left;
currY = e.clientY - canvas.getBoundingClientRect().top;
draw();
<html>
<body onload="init()">
<p>Below you can draw:</p>
<canvas id="can" style="position:absolute;">Below you can write:</canvas>
</body>【讨论】：
【参考方案13】：如果您在执行此操作时遇到问题，请告诉我。它使用 processing.js 并具有更改颜色和使绘制点越来越大的功能。
<html>
<head>
<!--script librarires-->
<script type="text/javascript" src="processing.js"></script>
<script type="text/javascript" src="init.js"></script>
<!--styles -->
<style type="text/css" src="stylesheet.css">
</style>
</head>
<body>
<!--toolbox -->
<div id="draggable toolbox"></div>
<script type="application/processing">
// new script
int prevx, prevy;
int newx, newy;
boolean cliked;
color c1 = #000000;
int largeur=2;
int ps = 20;
int px = 50;
int py = 50;
void setup()
size(500,500);
frameRate(25);
background(50);
prevx = mouseX;
prevy = mouseY;
cliked = false;
void draw()
//couleur
noStroke(0);
fill(#FFFFFF);//blanc
rect(px, py, ps, ps);
fill(#000000);
rect(px, py+(ps), ps, ps);
fill(#FF0000);
rect(px, py+(ps*2), ps, ps);
fill(#00FF00);
rect(px, py+(ps*3), ps, ps);
fill(#FFFF00);
rect(px, py+(ps*4), ps, ps);
fill(#0000FF);
rect(px, py+(ps*5), ps, ps);
//largeur
fill(#FFFFFF);
rect(px, py+(ps*7), ps, ps);
fill(#FFFFFF);
rect(px, py+(ps*8), ps, ps);
stroke(#000000);
line(px+2, py+(ps*7)+(ps/2), px+(ps-2), py+(ps*7)+(ps/2));
line(px+(ps/2), py+(ps*7)+1, px+(ps/2), py+(ps*8)-1);
line(px+2, py+(ps*8)+(ps/2), px+(ps-2), py+(ps*8)+(ps/2));
if(cliked==false)
prevx = mouseX;
prevy = mouseY;
if(mousePressed)
cliked = true;
newx = mouseX;
newy = mouseY;
strokeWeight(largeur);
stroke(c1);
line(prevx, prevy, newx, newy);
prevx = newx;
prevy = newy;
else
cliked= false;
void mouseClicked()
if (mouseX>=px && mouseX<=(px+ps))
//couleur
if (mouseY>=py && mouseY<=py+(ps*6))
c1 = get(mouseX, mouseY);
//largeur
if (mouseY>=py+(ps*7) && mouseY<=py+(ps*8))
largeur += 2;
if (mouseY>=py+(ps*8) && mouseY<=py+(ps*9))
if (largeur>2)
largeur -= 2;
</script><canvas></canvas>
</body>
</html>
【讨论】：
我不明白，但它开始处理。【参考方案14】：如果您的画布有背景图像，则必须进行一些调整才能使其正常工作，因为白色擦除技巧会隐藏背景。
这是带有代码的gist。
<html>
<script type="text/javascript">
var canvas, canvasimg, backgroundImage, finalImg;
var mouseClicked = false;
var prevX = 0;
var currX = 0;
var prevY = 0;
var currY = 0;
var fillStyle = "black";
var globalCompositeOperation = "source-over";
var lineWidth = 2;
function init()
var imageSrc = '/abstract-geometric-pattern_23-2147508597.jpg'
backgroundImage = new Image();
backgroundImage.src = imageSrc;
canvas = document.getElementById('can');
finalImg = document.getElementById('finalImg');
canvasimg = document.getElementById('canvasimg');
canvas.style.backgroundImage = "url('" + imageSrc + "')";
canvas.addEventListener("mousemove", handleMouseEvent);
canvas.addEventListener("mousedown", handleMouseEvent);
canvas.addEventListener("mouseup", handleMouseEvent);
canvas.addEventListener("mouseout", handleMouseEvent);
function getColor(btn)
globalCompositeOperation = 'source-over';
lineWidth = 2;
switch (btn.getAttribute('data-color'))
case "green":
fillStyle = "green";
break;
case "blue":
fillStyle = "blue";
break;
case "red":
fillStyle = "red";
break;
case "yellow":
fillStyle = "yellow";
break;
case "orange":
fillStyle = "orange";
break;
case "black":
fillStyle = "black";
break;
case "eraser":
globalCompositeOperation = 'destination-out';
fillStyle = "rgba(0,0,0,1)";
lineWidth = 14;
break;
function draw(dot)
var ctx = canvas.getContext("2d");
ctx.beginPath();
ctx.globalCompositeOperation = globalCompositeOperation;
if(dot)
ctx.fillStyle = fillStyle;
ctx.fillRect(currX, currY, 2, 2);
else
ctx.beginPath();
ctx.moveTo(prevX, prevY);
ctx.lineTo(currX, currY);
ctx.strokeStyle = fillStyle;
ctx.lineWidth = lineWidth;
ctx.stroke();
ctx.closePath();
function erase()
if (confirm("Want to clear"))
var ctx = canvas.getContext("2d");
ctx.clearRect(0, 0, canvas.width, canvas.height);
document.getElementById("canvasimg").style.display = "none";
function save()
canvas.style.border = "2px solid";
canvasimg.width = canvas.width;
canvasimg.height = canvas.height;
var ctx2 = canvasimg.getContext("2d");
// comment next line to save the draw only
ctx2.drawImage(backgroundImage, 0, 0);
ctx2.drawImage(canvas, 0, 0);
finalImg.src = canvasimg.toDataURL();
finalImg.style.display = "inline";
function handleMouseEvent(e)
if (e.type === 'mousedown')
prevX = currX;
prevY = currY;
currX = e.offsetX;
currY = e.offsetY;
mouseClicked = true;
draw(true);
if (e.type === 'mouseup' || e.type === "mouseout")
mouseClicked = false;
if (e.type === 'mousemove')
if (mouseClicked)
prevX = currX;
prevY = currY;
currX = e.offsetX;
currY = e.offsetY;
draw();
</script>
<body onload="init()">
<canvas id="can" style="position:absolute;top:10%;left:10%;border:2px solid;">
</canvas>
<div style="position:absolute;top:12%;left:43%;">Choose Color</div>
<div style="position:absolute;top:15%;left:45%;width:10px;height:10px;background:green;" data-color="green" onclick="getColor(this)"></div>
<div style="position:absolute;top:15%;left:46%;width:10px;height:10px;background:blue;" data-color="blue" onclick="getColor(this)"></div>
<div style="position:absolute;top:15%;left:47%;width:10px;height:10px;background:red;" data-color="red" onclick="getColor(this)"></div>
<div style="position:absolute;top:17%;left:45%;width:10px;height:10px;background:yellow;" data-color="yellow" onclick="getColor(this)"></div>
<div style="position:absolute;top:17%;left:46%;width:10px;height:10px;background:orange;" data-color="orange" onclick="getColor(this)"></div>
<div style="position:absolute;top:17%;left:47%;width:10px;height:10px;background:black;" data-color="black" onclick="getColor(this)"></div>
<div style="position:absolute;top:20%;left:43%;">Eraser</div>
<div style="position:absolute;top:22%;left:45%;width:15px;height:15px;background:white;border:2px solid;" data-color="eraser" onclick="getColor(this)"></div>
<canvas id="canvasimg" style="display:none;" ></canvas>
<img id="finalImg" style="position:absolute;top:10%;left:52%;display:none;" >
<input type="button" value="save" id="btn" size="30" onclick="save()" style="position:absolute;top:55%;left:10%;">
<input type="button" value="clear" id="clr" size="23" onclick="erase()" style="position:absolute;top:55%;left:15%;">
</body>
</html>
【讨论】：
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