Javascript color gradient

Using javascript with or without Jquery, I need to a create a gradient of colours based on a start and finish color. Is this possible to do programmatically?

The end colour is only ever going to be darker shade of the start colour and it's for an unordered list which I have no control over the number of li items. I'm looking for a solution that allows me to pick a start and end color, convert the hex value into RGB so it can be manipulated in code. The starting RGB values gets incremented by a step value calculated based upon the number of items.

so if the list had 8 items then the it needs to increment the seperate Red Green Blue values in 8 steps to achieve the final colour. Is there a better way to do it and if so where can I find some sample code?

Solution 1:

I created a JS library, RainbowVis-JS to solve this general problem. You just have to set the number of items using setNumberRange and set the start and end colour using setSpectrum. Then you get the hex colour code with colourAt.

var numberOfItems = 8;
var rainbow = new Rainbow(); 
rainbow.setNumberRange(1, numberOfItems);
rainbow.setSpectrum('red', 'black');
var s = '';
for (var i = 1; i <= numberOfItems; i++) {
    var hexColour = rainbow.colourAt(i);
    s += '#' + hexColour + ', ';
}
document.write(s); 
// gives:
// #ff0000, #db0000, #b60000, #920000, #6d0000, #490000, #240000, #000000,

You are welcome to look at the library's source code. :)

Solution 2:

Correct function to generate array of colors!

function hex (c) {
  var s = "0123456789abcdef";
  var i = parseInt (c);
  if (i == 0 || isNaN (c))
    return "00";
  i = Math.round (Math.min (Math.max (0, i), 255));
  return s.charAt ((i - i % 16) / 16) + s.charAt (i % 16);
}

/* Convert an RGB triplet to a hex string */
function convertToHex (rgb) {
  return hex(rgb[0]) + hex(rgb[1]) + hex(rgb[2]);
}

/* Remove '#' in color hex string */
function trim (s) { return (s.charAt(0) == '#') ? s.substring(1, 7) : s }

/* Convert a hex string to an RGB triplet */
function convertToRGB (hex) {
  var color = [];
  color[0] = parseInt ((trim(hex)).substring (0, 2), 16);
  color[1] = parseInt ((trim(hex)).substring (2, 4), 16);
  color[2] = parseInt ((trim(hex)).substring (4, 6), 16);
  return color;
}

function generateColor(colorStart,colorEnd,colorCount){

	// The beginning of your gradient
	var start = convertToRGB (colorStart);    

	// The end of your gradient
	var end   = convertToRGB (colorEnd);    

	// The number of colors to compute
	var len = colorCount;

	//Alpha blending amount
	var alpha = 0.0;

	var saida = [];
	
	for (i = 0; i < len; i++) {
		var c = [];
		alpha += (1.0/len);
		
		c[0] = start[0] * alpha + (1 - alpha) * end[0];
		c[1] = start[1] * alpha + (1 - alpha) * end[1];
		c[2] = start[2] * alpha + (1 - alpha) * end[2];

		saida.push(convertToHex (c));
		
	}
	
	return saida;
	
}

// Exemplo de como usar


var tmp = generateColor('#000000','#ff0ff0',10);

for (cor in tmp) {
  $('#result_show').append("<div style='padding:8px;color:#FFF;background-color:#"+tmp[cor]+"'>COLOR "+cor+"° - #"+tmp[cor]+"</div>")
 
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id="result_show"></div>

Javascript color gradient

Solution 1:

Solution 2:

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