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问题:

I want to know how to make a color picker with jQuery that will allow you to click somewhere on the page and return the hex color value of the color that you clicked on.

I know that it is possible with either javascript or jquery as not only do they have lots of color picker plugins, but I have and extension for Chrome that has that same exact functionality.

Any ideas?

回答1:

Bind a global click or mouseup event listener. Then, use canvas to obtain the pixel information. The pixel positions can be retrieved through the event object (event.pageX, event.pageY).

See below for an example, which should work in future versions of FireFox. Currently, for security reasons, the drawWindow method is disabled for web pages. It should work in extensions, though. If you're truly interested, see the links for the similar methods in Chrome, Safari and Internet Explorer.

var canvas = $("<canvas>"); //Create the canvas element

//Create a layer which overlaps the whole window
canvas.css({position:"fixed", top:"0", left:"0",
            width:"100%", height:"100%", "z-index":9001});

//Add an event listener to the canvas element
canvas.click(function(ev){
    var x = ev.pageX, y = ev.pageY;
    var canvas = this.getContext("2d");
    canvas.drawWindow(window, x, y, 1, 1, "transparent");
    var data = canvas.getImageData(0, 0, 1, 1).data;
    var hex = rgb2hex(data[0], data[1], data[2]);
    alert(hex);
    $(this).remove();
});

canvas.appendTo("body:first"); //:first, in case of multiple <body> tags (hmm?)

//Functions used for conversion from RGB to HEX
function rgb2hex(R,G,B){return num2hex(R)+num2hex(G)+num2hex(B);}
function num2hex(n){
    if (!n || !parseInt(n)) return "00";
    n = Math.max(0,Math.floor(Math.round(n),255)).toString(16);
    return n.length == 1 ? "0"+n : n;
}

References

Canvas examples - Learn more about canvas
drawWindow - FireFox method
visibleContentAsDataURL - Safari extensions
chrome.tabs.captureVisibleTab - Chrome extensions
HTA ActiveX control - Internet Explorer

回答2:

Those plugins don't work by knowing the color of the pixel under the mouse; they work because the colors in the picker are laid out according to a mathematical formula, and by knowing that formula and where you clicked the mouse, the plugin can find out what color belongs there. JavaScript doesn't give you any way to get an image of the page or the "color under the cursor".

回答3:

I had this problem recently, by default IE returns hex colours whereas all the good browsers return rgb values, I simply put conditions to deal with both strings, this would be more efficient..

however I think this function does the trick if you really need it

function RGBToHex(rgb) { 
var char = "0123456789ABCDEF"; 
return String(char.charAt(Math.floor(rgb / 16))) + String(char.charAt(rgb - (Math.floor(rgb / 16) * 16))); 
}