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Posted By

koncept on 04/13/08


Tagged

hex colour color convert inverse


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jonhenshaw


Inverse Hex Color

Published in: PHP 

Sorry to those who previously bookmarked this. In an attempt to delete a previous version that had a logic flaw, I accidently deleted the entire snippet. Anyway, here is a much improved version. Any comments/suggestions are always welcome.

Plain TextExpand 
  1. <?php
  2. /**
  3.  * Inverses a provided hex color. If you pass a hex string with a 
  4.  * hash(#), the function will return a string with a hash prepended
  5.  * @param string $color Hex color to flip
  6.  * @return string Reversed hex color
  7.  * @author Koncept
  8.  * 
  9.  * Last Update: 2008-04-13
  10.  */
  11. function inverseHex( $color )
  12. {
  13. 	$color       = trim($color);
  14. 	$prependHash = FALSE;
  15.  
  16. 	if(strpos($color,'#')!==FALSE) {
  17. 		$prependHash = TRUE;
  18. 		$color       = str_replace('#',NULL,$color);
  19. 	}
  20.  
  21. 	switch($len=strlen($color)) {
  22. 		case 3:
  23. 			$color=preg_replace("/(.)(.)(.)/","\\1\\1\\2\\2\\3\\3",$color);
  24. 		case 6:
  25. 			break;
  26. 		default:
  27. 			trigger_error("Invalid hex length ($len). Must be (3) or (6)", E_USER_ERROR);
  28. 	}
  29.  
  30. 	if(!preg_match('/[a-f0-9]{6}/i',$color)) {
  31. 		$color = htmlentities($color);
  32. 		trigger_error( "Invalid hex string #$color", E_USER_ERROR );
  33. 	}
  34.  
  35. 	$r = dechex(255-hexdec(substr($color,0,2)));
  36. 	$r = (strlen($r)>1)?$r:'0'.$r;
  37. 	$g = dechex(255-hexdec(substr($color,2,2)));
  38. 	$g = (strlen($g)>1)?$g:'0'.$g;
  39. 	$b = dechex(255-hexdec(substr($color,4,2)));
  40. 	$b = (strlen($b)>1)?$b:'0'.$b;
  41.  
  42. 	return ($prependHash?'#':NULL).$r.$g.$b;
  43. }
  44.  
  45. // Demo
  46. echo inverseHex('#000000'); // #ffffff
  47. ?>

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