Мне показали этот скрипт , который является модификацией http://www.robodesign.ro/coding/canvas-paint/20090423/
Он очень хорошо работает в Fx 10, но совсем не в Chrome.
DEMO
Я избавился от предупреждения Chrome об устаревшем event.layerX / Y, поменяв местами offsetX и layerX, но он все равно не рисует.
Должно быть что-то очень простое.
ОБНОВЛЕНИЕ : и это было - закомментировав два context.moveTo(ev._x, ev._y); сделали свое дело
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Paint</title>
<style type="text/css"><!--
#container { position: relative; }
#imageView { border: 1px solid #000; }
--></style>
</head>
<body BGCOLOR="#CCFFFF">
<div id="container">
<canvas id="imageView" width="700" height="643" margin: 0 auto>
<p>Unfortunately, your browser is currently unsupported by our web
application. We are sorry for the inconvenience. Please use one of the
supported browsers listed below, or draw the image you want using an
offline tool.</p>
<p>Supported browsers: <a href="http://www.opera.com">Opera</a>, <a
href="http://www.mozilla.com">Firefox</a>, <a
href="http://www.apple.com/safari">Safari</a>, and <a
href="http://www.konqueror.org">Konqueror</a>.</p>
</canvas>
</div>
<script type="text/javascript">
/* © 2009 ROBO Design
* http://www.robodesign.ro
*/
// Keep everything in anonymous function, called on window load.
if(window.addEventListener) {
window.addEventListener('load', function () {
var canvas, context, tool;
function init () {
// Find the canvas element.
canvas = document.getElementById('imageView');
if (!canvas) {
alert('Error: I cannot find the canvas element!');
return;
}
if (!canvas.getContext) {
alert('Error: no canvas.getContext!');
return;
}
// Get the 2D canvas context.
context = canvas.getContext('2d');
if (!context) {
alert('Error: failed to getContext!');
return;
}
var img=new Image();
img.onload = function(){
context.drawImage(img,0,0);
};
img.src=" PainDiagram.png";
// Pencil tool instance.
tool = new tool_pencil();
// Attach the mousedown, mousemove and mouseup event listeners.
canvas.addEventListener('mousedown', ev_canvas, false);
canvas.addEventListener('mousemove', ev_canvas, false);
canvas.addEventListener('mouseup', ev_canvas, false);
}
// This painting tool works like a drawing pencil which tracks the mouse
// movements.
function tool_pencil () {
var tool = this;
this.started = false;
// This is called when you start holding down the mouse button.
// This starts the pencil drawing.
this.mousedown = function (ev) {
context.beginPath();
context.lineWidth = 5;
context.lineCap = "round";
context.globalAlpha=0.01;
context.shadowColor="red";
context.shadowBlur=10;
context.strokeStyle = "red"; // line color
context.moveTo(ev._x, ev._y);
tool.started = true;
};
// This function is called every time you move the mouse. Obviously, it only
// draws if the tool.started state is set to true (when you are holding down
// the mouse button).
this.mousemove = function (ev) {
if (tool.started) {
//var p = context.getImageData(ev._x, ev._y, 1, 1).data;
//if(p[0]==255 && p[1]==204 && p[2]==153){
context.moveTo(ev._x, ev._y);
context.lineTo(ev._x, ev._y);
context.stroke();
//}
}
};
// This is called when you release the mouse button.
this.mouseup = function (ev) {
if (tool.started) {
tool.mousemove(ev);
tool.started = false;
}
};
}
// The general-purpose event handler. This function just determines the mouse
// position relative to the canvas element.
function ev_canvas (ev) {
if (ev.offsetX || ev.offsetX == 0) { // Opera and WebKit
ev._x = ev.offsetX;
ev._y = ev.offsetY;
}
else if (ev.layerX || ev.layerX == 0) { // Firefox
ev._x = ev.layerX;
ev._y = ev.layerY;
}
// Call the event handler of the tool.
var func = tool[ev.type];
if (func) {
func(ev);
}
}
init();
}, false); }
// vim:set spell spl=en fo=wan1croql tw=80 ts=2 sw=2 sts=2 sta et ai cin fenc=utf-8 ff=unix:
</script>
</body>
</html>