http://jsbin.com/urubev/9/edit
在您的 HTML 中，您的选项值中有一些 javascript 代码。他们需要改成这样：
<select id="dtool">
<option value="pencil">Pencil</option>
<option value="spray">Spray</option>
</select>
在 JS 中，我只是将您已经提供的代码片段移到了 spray 对象内。
//These are the variables used throughout the javascript
//var points = new Array();
var outlineImage = new Image();
radius = 15
var colorPurple = "#cb3594"; //variable for purple colour
var colorGreen = "#659b41"; //variable for green colour
var colorYellow = "#ffcf33";//variable for yellow colour
var colorBlack = "#000000";//variable for black colour
var CurrentColor = colorBlack; //variable for current colour
//used to change the colour of the drawing tool
function changeColor( color_code ) {
CurrentColor =color_code;
}
//this function will allow you clear the canvas
function clearCanvas(){
context.clearRect(0, 0, canvas.width, canvas.height);
}
if (window.addEventListener) {
window.addEventListener('load', function () {
var canvas, context;
// The active tool instance.
var tool;
var tool_default = 'spray';
function init() {
// Find the canvas element.
canvas = document.getElementById('imageView');//this is used to get a element id for 'imageView' the cnavas
if (!canvas) {
alert('Error: I cannot find the canvas element!');//if it fails to get the canvas then it will diplay this error
return;
}
if (!canvas.getContext) {
alert('Error: no canvas.getContext!');//if it fails to get the context then it will diplay this error
return;
}
// Get the 2D canvas context.
context = canvas.getContext('2d');// used to get canavs context to '2d'
if (!context) {
alert('Error: failed to getContext!');//if it fails to get the context then it will diplay this error
return;
}
// Get the tool select input.
var tool_select = document.getElementById('dtool');
if (!tool_select) {
alert('Error: failed to get the dtool element!');
return;
}
tool_select.addEventListener('change', ev_tool_change, false);
// Activate the default tool.
if (tools[tool_default]) {
tool = new tools[tool_default]();
tool_select.value = tool_default;
}
// 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);
}
// The event handler for any changes made to the tool selector.
function ev_tool_change (ev) {
if (tools[this.value]) {
tool = new tools[this.value]();
}
}
// This object holds the implementation of each drawing tool.
var tools = {};
// This painting tool works like a drawing pencil which tracks the mouse
// movements.
tools.pencil = function() {
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.strokeStyle = CurrentColor;
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) {
context.strokeStyle = CurrentColor;
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;
}
};
}
tools.spray = function() {
var tool = this;
this.started = false;
this.mousedown = function (ev) {
context.beginPath();
context.strokeStyle = CurrentColor;
context.moveTo(ev._x, ev._y);
tool.started = true;
};
this.mousemove = function (ev) {
if (tool.started) {
context.strokeStyle = CurrentColor;
context.arc(
ev._x + Math.cos( Math.random() * Math.PI * 2 ) * radius * Math.random(),
ev._y + Math.sin( Math.random() * Math.PI * 2 ) * radius * Math.random(),
1,
0, Math.PI * 2, false
);
context.fill();
}
};
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 (navigator.appName == 'Microsoft Internet Explorer' || navigator.vendor == 'Google Inc.' || navigator.vendor == 'Apple Computer, Inc.') { // IE or Chrome
ev._x = ev.offsetX;
ev._y = ev.offsetY;
} else if (ev.layerX || ev.layerX == 0) { // Firefox
ev._x = ev.layerX - this.offsetLeft;
ev._y = ev.layerY - this.offsetTop;
} else if (ev.offsetX || ev.offsetX == 0) { // Opera
ev._x = ev.offsetX;
ev._y = ev.offsetY;
}
// Call the event handler of the tool.
var func = tool[ev.type];
if (func) {
func(ev);
}
// points.push(ev);
}
init();
}, false);
}