<?php

	/*----------------------------------------------------------------------
		Colour Tools
		============
		Colour Tools is a class that contains various functions for
		manipulating colours in PHP. It includes basic conversion functions,
		a gradient function, an invert function and a set of functions for
		comparing two colours for brightness and colour contrast, according
		to the W3C recommendations.
		
		Usage:
			echo ColourTools::compare('ffffff', '000000');
				
		Version 0.5
		Copyright Jack Sleight - www.reallyshiny.com
		This script is licensed under the:
			Creative Commons Attribution-ShareAlike 2.5 License
	----------------------------------------------------------------------*/

	class ColourTools
	{
		/*--------------------------------------------------
			Convert Hex code string to RGB array
		--------------------------------------------------*/

		function hexToRgb($hex)
		{
			$hex = preg_replace('/^#/', '', $hex);
			return array(
				'r' => hexdec(substr($hex, 0, 2)),
				'g' => hexdec(substr($hex, 2, 2)),
				'b' => hexdec(substr($hex, 4, 2))
			);
		}
	
		/*--------------------------------------------------
			Convert RGB array to Hex code string
		--------------------------------------------------*/

		function rgbToHex($rgb)
		{
			return sprintf('%02x', $rgb['r']).sprintf('%02x', $rgb['g']).sprintf('%02x', $rgb['b']);
		}
	
		/*--------------------------------------------------
			Create a gradient from one colour to another
		--------------------------------------------------*/

		function gradient($col1, $col2, $steps)
		{
			$col1 = ColourTools::hexToRgb($col1);
			$col2 = ColourTools::hexToRgb($col2);
			
			$step = array(
				'r' => ($col1['r'] - $col2['r']) / ($steps - 1),
				'g' => ($col1['g'] - $col2['g']) / ($steps - 1),
				'b' => ($col1['b'] - $col2['b']) / ($steps - 1)
			);
			$gradient = array();
			
			for($i = 0; $i <= $steps; $i++) {
				$colour = array(
					'r' => round($col1['r'] - ($step['r'] * $i)),
					'g' => round($col1['g'] - ($step['g'] * $i)),
					'b' => round($col1['b'] - ($step['b'] * $i))
				);
				$gradient[] = ColorTools::rgbToHex($colour);
			}
			
			return $gradient;
		}
	
		/*--------------------------------------------------
			Invert a colour
		--------------------------------------------------*/

		function invert($col1)
		{
			$col1 = ColourTools::hexToRgb($col1);
			$col2 = array(
				'r' => 256 - $col1['r'],
				'g' => 256 - $col1['g'],
				'b' => 256 - $col1['b']
			);
			return ColourTools::rgbToHex($col2);
		}
	
		/*--------------------------------------------------
			Checks if two colours adhere to the W3C
			recommendations for brightness and colour 
			contrast
		--------------------------------------------------*/

		function compare($col1, $col2)
		{
			$brightnessDifference = ColourTools::brightnessDifference($col1, $col2);
			$colourDifference = ColourTools::colourDifference($col1, $col2);
			return (($brightnessDifference > 125) && ($colourDifference > 500)) ? true : false;
		}
		
		/*--------------------------------------------------
			Get the brightness value of a colour
		--------------------------------------------------*/

		function brightness($col)
		{
			$col = ColourTools::hexToRgb($col);
			return (($col['r'] * 299) + ($col['g'] * 587) + ($col['b'] * 114)) / 1000;
		}
		
		/*--------------------------------------------------
			Get the brightness difference of two colours
		--------------------------------------------------*/

		function brightnessDifference($col1, $col2)
		{
			return abs(ColourTools::brightness($col1) - ColourTools::brightness($col2));
		}
		
		/*--------------------------------------------------
			Get the colour difference of two colours
		--------------------------------------------------*/

		function colourDifference($col1, $col2)
		{
			$col1 = ColourTools::hexToRgb($col1);
			$col2 = ColourTools::hexToRgb($col2);
			return
				(max($col1['r'], $col2['r']) - min($col1['r'], $col2['r'])) +
				(max($col1['g'], $col2['g']) - min($col1['g'], $col2['g'])) +
				(max($col1['b'], $col2['b']) - min($col1['b'], $col2['b']));
		}
	
	}

?>