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HTML5 Canvas 颜色选择器

这段代码是用HTML5来创建一个网页颜色选择器。首先在Canvas画一幅图,然后添加鼠标事件 “鼠标移动”,“鼠标点击”。在鼠标移动的时候,显示当前划过的颜色预览,在鼠标点击的时候,选中当前颜色,显示颜色的细节。
[代码] [HTML]代码
<!DOCTYPE html>
<html lang="en" >
    <head>
        <meta charset="utf-8" />
        <title><A title=HTML5 href="http://www.xyhtml5.com/">HTML5</A> canvas - Image color picker | Script Tutorials</title>
        <link href="<A title=css href="http://www.xyhtml5.com/css3">css</A>/main.<A title=css href="http://www.xyhtml5.com/css3">css</A>" rel="stylesheet" type="text/css" /> 
        <script type="text/<A title=javascript href="http://www.xyhtml5.com/javascript">javascript</A>" src="js/jquery-1.5.2.min.js"></script>
        <script type="text/<A title=javascript href="http://www.xyhtml5.com/javascript">javascript</A>" src="js/script.js"></script>
    </head>
    <body>
        <div class="container">
            <div class="column1">
                <canvas id="panel" width="500" height="333"></canvas>
            </div>
            <div class="column2">
                <div><input type="button" value="Next image" id="swImage" /></div>
                <div>Preview:</div>
                <div id="preview"></div>
                <div>Color:</div>
                <div>R: <input type="text" id="rVal" /></div>
                <div>G: <input type="text" id="gVal" /></div>
                <div>B: <input type="text" id="bVal" /></div>
                <div>RGB: <input type="text" id="rgbVal" /></div>
                <div>RGBA: <input type="text" id="rgbaVal" /></div>
                <div>HEX: <input type="text" id="hexVal" /></div>
                <hr />
            </div>
            <div style="clear:both;"></div>
        </div>
        <footer>
            <h2>HTML5 canvas - Image color picker</h2>
            <a href="http://www.script-tutorials.com/html5-canvas-image-color-picker/" class="stuts">Back to original tutorial on <span>Script Tutorials</span></a>
        </footer>
    </body>
</html>
[CSS]代码
*{
    margin:0;
    padding:0;
}
 
body {
    background-color:#bababa;
    color:#fff;
    font:14px/1.3 Arial,sans-serif; 
}
 
footer {
    background-color:#212121;
    bottom:0;
    box-shadow: 0 -1px 2px #111111;
    display:block;
    height:70px;
    left:0;
    position:fixed;
    width:100%;
    z-index:100;
}
 
footer h2{
    font-size:22px;
    font-weight:normal;
    left:50%;
    margin-left:-400px;
    padding:22px 0;
    position:absolute;
    width:540px;
}
 
footer a.stuts,a.stuts:visited{
    border:none;
    text-decoration:none;
    color:#fcfcfc;
    font-size:14px;
    left:50%;
    line-height:31px;
    margin:23px 0 0 110px;
    position:absolute;
    top:0;
}
 
footer .stuts span {
    font-size:22px;
    font-weight:bold;
    margin-left:5px;
}
 
.container {
    color:#000;
    margin:20px auto;
    position:relative;
    width:730px;
}
 
.column1 {
    float:left;
    width:500px;
}
 
.column2 {
    float:left;
    padding-left:20px;
    width:170px;
}
 
#panel {
    border:1px #000 solid;
    box-shadow:4px 6px 6px #444444;
    cursor:crosshair;
}
 
.column2 > div {
    margin-bottom:10px;
}
 
#swImage {
    border:1px #000 solid;
    box-shadow:2px 3px 3px #444444;
    cursor:pointer;
    height:25px;
    line-height:25px;
 
    border-radius:3px;
    -moz-border-radius:3px;
    -webkit-border-radius:3px;
}
 
#swImage:hover {
    margin-left:2px;
}
 
#preview {
    border:1px #000 solid;
    box-shadow:2px 3px 3px #444444;
    height:80px;
    width:80px;
 
    border-radius:3px;
    -moz-border-radius:3px;
    -webkit-border-radius:3px;
}
 
.column2 input[type=text] {
    float:right;
    width:110px;
}
[JavaScript]代码
var canvas;
var ctx;
 
var images = [ // predefined array of used images
    'images/pic1.jpg',
    'images/pic2.jpg',
    'images/pic3.jpg',
    'images/pic4.jpg',
    'images/pic5.jpg',
    'images/pic6.jpg',
    'images/pic7.jpg',
    'images/pic8.jpg',
    'images/pic9.jpg',
    'images/pic10.jpg'
];
var iActiveImage = 0;
 
$(function(){
 
    // drawing active image
    var image = new Image();
    image.onload = function () {
        ctx.drawImage(image, 0, 0, image.width, image.height); // draw the image on the canvas 
    }
    image.src = images[iActiveImage];
 
    // creating canvas object
    canvas = document.getElementById('panel');
    ctx = canvas.getContext('2d');
 
    $('#panel').mousemove(function(e) { // mouse move handler
        var canvasOffset = $(canvas).offset();
        var canvasX = Math.floor(e.pageX - canvasOffset.left);
        var canvasY = Math.floor(e.pageY - canvasOffset.top);
 
        var imageData = ctx.getImageData(canvasX, canvasY, 1, 1);
        var pixel = imageData.data;
 
        var pixelColor = "rgba("+pixel[0]+", "+pixel[1]+", "+pixel[2]+", "+pixel[3]+")";
        $('#preview').css('backgroundColor', pixelColor);
    });
 
    $('#panel').click(function(e) { // mouse click handler
        var canvasOffset = $(canvas).offset();
        var canvasX = Math.floor(e.pageX - canvasOffset.left);
        var canvasY = Math.floor(e.pageY - canvasOffset.top);
 
        var imageData = ctx.getImageData(canvasX, canvasY, 1, 1);
        var pixel = imageData.data;
 
        $('#rVal').val(pixel[0]);
        $('#gVal').val(pixel[1]);
        $('#bVal').val(pixel[2]);
 
        $('#rgbVal').val(pixel[0]+','+pixel[1]+','+pixel[2]);
        $('#rgbaVal').val(pixel[0]+','+pixel[1]+','+pixel[2]+','+pixel[3]);
        var dColor = pixel[2] + 256 * pixel[1] + 65536 * pixel[0];
        $('#hexVal').val( '#' + dColor.toString(16) );
    }); 
 
    $('#swImage').click(function(e) { // switching images
        iActiveImage++;
        if (iActiveImage >= 10) iActiveImage = 0;
        image.src = images[iActiveImage];
    });
});