Mar*_*oma 20 javascript canvas
如何在画布元素上自由绘制(使用我的鼠标/手指),就像你可以用铅笔画画一样？
有很多问题需要在画布上实现免费手绘:
所以我认为提出一个参考问题是一个好主意,每个答案都是社区维基,并且包含对一个JavaScript库/纯JavaScript如何在画布上绘画的解释.
答案应该是社区维基并使用以下模板:
## [Name of library](Link to project page)
### Simple example
A basic, complete example. That means it has to contain HTML
and JavaScript. You can start with this:
<!DOCTYPE html>
<html>
<head>
<title>Simple example</title>
<script type='text/javascript' src='http://cdnjs.com/[your library]'></script>
<style type='text/css'>
#sheet {
border:1px solid black;
}
</style>
<script type='text/javascript'>
window.onload=function(){
// TODO: Adjust
}
</script>
</head>
<body>
<canvas id="sheet" width="400" height="400"></canvas>
</body>
</html>
If possible, this example should work with both, mouse and touch events.
[JSFiddle](Link to code on jsfiddle.net)
This solution works with:
<!-- Please test it the following way: Write "Hello World"
Problems that you test this way are:
* Does it work at all?
* Are lines separated?
* Does it get slow when you write too much?
-->
* Desktop computers:
* [Browser + Version list]
* Touch devices:
* [Browser + Version list] on [Device name]
### Import / Export
Some explanations how to import / export user drawn images.
### Line smoothing
Explanations about how to manipulate the line the user draws.
This can include:
* Bézier curves
* Controlling thickness of lines
<!DOCTYPE html>
<html>
<head>
<title>Simple example</title>
<script type='text/javascript' src='http://cdnjs.cloudflare.com/ajax/libs/fabric.js/1.4.0/fabric.min.js'></script>
<style type='text/css'>
#sheet {
border:1px solid black;
}
</style>
<script type='text/javascript'>
window.onload=function(){
var canvas = new fabric.Canvas('sheet');
canvas.isDrawingMode = true;
canvas.freeDrawingBrush.width = 5;
canvas.freeDrawingBrush.color = "#ff0000";
}
</script>
</head>
<body>
<canvas id="sheet" width="400" height="400"></canvas>
</body>
</html>
canvas.freeDrawingBrush.width.canvas.freeDrawingBrush.color.此解决方案适用于:
只能通过序列化完整的画布来实现,请参阅教程
是自动完成的,似乎无法停用它.
<!DOCTYPE html>
<html>
<head>
<title>Simple example</title>
<style type='text/css'>
#sheet {
border:1px solid black;
}
</style>
</head>
<body>
<canvas id="sheet" width="400" height="400"></canvas>
<script type='text/javascript'>
/*jslint browser:true */
"use strict";
var context = document.getElementById('sheet').getContext("2d");
var canvas = document.getElementById('sheet');
context = canvas.getContext("2d");
context.strokeStyle = "#ff0000";
context.lineJoin = "round";
context.lineWidth = 5;
var clickX = [];
var clickY = [];
var clickDrag = [];
var paint;
/**
* Add information where the user clicked at.
* @param {number} x
* @param {number} y
* @return {boolean} dragging
*/
function addClick(x, y, dragging) {
clickX.push(x);
clickY.push(y);
clickDrag.push(dragging);
}
/**
* Redraw the complete canvas.
*/
function redraw() {
// Clears the canvas
context.clearRect(0, 0, context.canvas.width, context.canvas.height);
for (var i = 0; i < clickX.length; i += 1) {
if (!clickDrag[i] && i == 0) {
context.beginPath();
context.moveTo(clickX[i], clickY[i]);
context.stroke();
} else if (!clickDrag[i] && i > 0) {
context.closePath();
context.beginPath();
context.moveTo(clickX[i], clickY[i]);
context.stroke();
} else {
context.lineTo(clickX[i], clickY[i]);
context.stroke();
}
}
}
/**
* Draw the newly added point.
* @return {void}
*/
function drawNew() {
var i = clickX.length - 1
if (!clickDrag[i]) {
if (clickX.length == 0) {
context.beginPath();
context.moveTo(clickX[i], clickY[i]);
context.stroke();
} else {
context.closePath();
context.beginPath();
context.moveTo(clickX[i], clickY[i]);
context.stroke();
}
} else {
context.lineTo(clickX[i], clickY[i]);
context.stroke();
}
}
function mouseDownEventHandler(e) {
paint = true;
var x = e.pageX - canvas.offsetLeft;
var y = e.pageY - canvas.offsetTop;
if (paint) {
addClick(x, y, false);
drawNew();
}
}
function touchstartEventHandler(e) {
paint = true;
if (paint) {
addClick(e.touches[0].pageX - canvas.offsetLeft, e.touches[0].pageY - canvas.offsetTop, false);
drawNew();
}
}
function mouseUpEventHandler(e) {
context.closePath();
paint = false;
}
function mouseMoveEventHandler(e) {
var x = e.pageX - canvas.offsetLeft;
var y = e.pageY - canvas.offsetTop;
if (paint) {
addClick(x, y, true);
drawNew();
}
}
function touchMoveEventHandler(e) {
if (paint) {
addClick(e.touches[0].pageX - canvas.offsetLeft, e.touches[0].pageY - canvas.offsetTop, true);
drawNew();
}
}
function setUpHandler(isMouseandNotTouch, detectEvent) {
removeRaceHandlers();
if (isMouseandNotTouch) {
canvas.addEventListener('mouseup', mouseUpEventHandler);
canvas.addEventListener('mousemove', mouseMoveEventHandler);
canvas.addEventListener('mousedown', mouseDownEventHandler);
mouseDownEventHandler(detectEvent);
} else {
canvas.addEventListener('touchstart', touchstartEventHandler);
canvas.addEventListener('touchmove', touchMoveEventHandler);
canvas.addEventListener('touchend', mouseUpEventHandler);
touchstartEventHandler(detectEvent);
}
}
function mouseWins(e) {
setUpHandler(true, e);
}
function touchWins(e) {
setUpHandler(false, e);
}
function removeRaceHandlers() {
canvas.removeEventListener('mousedown', mouseWins);
canvas.removeEventListener('touchstart', touchWins);
}
canvas.addEventListener('mousedown', mouseWins);
canvas.addEventListener('touchstart', touchWins);
</script>
</body>
</html>
context.lineWidth.strokeStyle.此解决方案适用于:
它不起作用
导入和导出图像可以通过导入/导出完成clickX,clickY和clickDrag.
最终可以通过替换来实现lineTo()与bezierCurveTo()
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