javascript - html5:canvas.getImageData无法正常工作-为什么？

我尝试从 Canvas 背景图像中获取所选像素的颜色，但是我所得到的(作为颜色)是0000。
你能帮助我吗？我的错误在哪里？

我的代码(js):

var canvas;
var mouse_position = [];
var color;

$(document).ready(function(){
    canvas_element = $('<canvas></canvas>');
    canvas = canvas_element.get(0).getContext("2d");
    canvas_element.appendTo('body');
    init_canvas();
});

function init_canvas(){
    var img = new Image();
    img.src = 'static/img/albatros.jpg';
    img.width = 600;
    img.height = 800;
    canvas.drawImage(img, 0, 0);

    $(document).mousemove(function(e){
        if(e.offsetX){
            mouse_position.x = e.offsetX;
            mouse_position.y = e.offsetY;
        }else if(e.layerY){
            mouse_position.x = e.layerX;
            mouse_position.y = e.layerY;
        }

        show_color();

    });
}


function show_color(){
    color  = canvas.getImageData(mouse_position.x,mouse_position.y,1,1).data;
    console.info("red: " + color[0] + " green: " + color[1] + " blue: " + color[2] + "alpha: " +color[3]);

}

最佳答案

我编写了脚本的新版本，现在可以正常工作了。
我误解了getImageData参数。
这是新版本:

var path = 'static/img/albatros.jpg',
color = new Array();
img = new Image();
img.src=path;
canvas = document.createElement('canvas');
canvas.id = 'canvas';
canvas.width = img.width;
canvas.height = img.height;
ccontext = null;

$(document).ready(function(){
    $('body').prepend(canvas);
    init_canvas();
});

function init_canvas(){
    ccontext = canvas.getContext("2d");
    ccontext.drawImage(img, 0, 0);
    imgData = ccontext.getImageData(0, 0, $('#canvas').width(),  $('#canvas').height());
    for(i = imgData.data.length; i--;){
        color[i] = imgData.data[i];
    }
}

$('#canvas').live('mousemove', function (e) {
   var offset = $('#canvas').offset();
    var eX = e.pageX - this.offsetLeft;
    var eY = e.pageY - this.offsetTop;
    var z = eY * this.width * 4;
    var s = eX * 4;
    console.info("red: " + imgData.data[z+s] + " green: " + imgData.data[z+s+1] + " blue: "+ imgData.data[z+s+2] + ' alpha: ' +imgData.data[z+s+3]);
});

关于javascript - html5:canvas.getImageData无法正常工作-为什么？，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/6869989/