html5 canvas图片渐变

浏览数：35 / 时间：2015年06月09日

<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>无标题文档</title>
<script>
window.onload = function ()
{
    var oc = document.getElementById(‘c1‘);
    var ogc = oc.getContext(‘2d‘);
    
    var yimg = new Image();
    yimg.onload = function ()
    {
        draw(this);
    }
    yimg.src = ‘img/5-5.jpg‘;
    
    function draw(obj)
    {
        oc.width = obj.width;
        oc.height = obj.height*2;
        
        ogc.drawImage(obj,0,0);
        var oimg = ogc.getImageData(0,0,obj.width,obj.height);
        var w = oimg.width;
        var h = oimg.height;
        
        var newimg = ogc.createImageData(obj.width,obj.height);
        for(var i = 0; i < h; i++)
        {
            for(var j = 0; j < w; j++)
            {
                var color = getXY(oimg,j,i)
                var result = [];
                result[0] = 255 - color[0];
                result[1] = 255 - color[1];
                result[2] = 255 - color[2];
                result[3] = 255*i/h;
                
                setXY(newimg,j,h-i,result);
            }
        }
        
        ogc.putImageData(newimg,0,obj.height);
    }
    
    function getXY(obj,x,y)
    {
        var w = obj.width;
        var h = obj.height;
        var d = obj.data;
        
        var color = [];
        
        color[0] = d[ 4*(y*w+x)];
        color[1] = d[ 4*(y*w+x) +1];
        color[2] = d[ 4*(y*w+x) +2];
        color[3] = d[ 4*(y*w+x) +3];
        
        return color;
    }
    
    
    function setXY(obj,x,y,color)
    {
        var w = obj.width;
        var h = obj.height;
        var d = obj.data;
        
        d[ 4*(y*w+x)] = color[0];
        d[ 4*(y*w+x) +1] = color[1];
        d[ 4*(y*w+x) +2] = color[2];
        d[ 4*(y*w+x) +3] = color[3];
        
    }
}
</script>
<style>
body{
    background:pink;
    }
#c1{
    background:white;
    }    
</style>
</head>

<body>
<canvas id="c1" width="400" height="800"></canvas>
</body>
</html>