<?
  /**
   * phpOpenCaptcha 1.0
   * (c) by Mathias Krebs, mathias.krebs(at)gmail.com, 2008
   * license: LGPL
   */
  
  /**
   * Initialize the random number generator.
   */
  function make_seed()
  {
    list($usec, $sec) = explode(' ', microtime());
    return (float) $sec + ((float) $usec * 100000);
  }
  
  /**
   * Get a sequnce of lower case random letters
   * @param  string	The lenght of the sequence.
   * @return string The random sequence.
   */
  function getRandomCode($aLength)
  {
    srand(make_seed());
  
    $aString = "";
    for ($i=0;$i<$aLength;$i++)
    {
      $randval = rand(0,25) + 97;
      $aString .= chr($randval);
    }
    
    return $aString;
  }

  /**
   * Get the color at a given point in the image.
   * Outside the image, a default color is given.
   * @param resource The image.
   * @param int      x-location of the point.
   * @param int      y-location of the point.
   * @param array    The default color.
   */
  function getColorAt($aIm,$aX,$aY,$defaultColor)
  {
    $aWidth  = imagesx($aIm);
    $aHeight = imagesy($aIm);
    if ($aX < 0 || $aX >= $aWidth || $aY < 0 || $aY >= $aHeight)
    {
      return $defaultColor;
    }
    else
    {
      $pos   = imagecolorat($aIm,$aX,$aY);
      $color = imagecolorsforindex($aIm, $pos);
      return $color;
    }
  }

  /**
   * Applies a (gaussian) matrix at a given point in the image.
   * @param  resource The image.
   * @param  int      x-location of the point.
   * @param  int      y-location of the point.
   * @param  array    The (gaussian) matrix.
   * @param  int      The sum of all weights in the matrix.
   * @param  array    The default (background) color of the image.
   * @return array    Rgb value of point after gaussian filter application.
   */
  function getGaussianAt($aIm,$aX,$aY,$aMatrix,$aSum,$defaultColor)
  {
    $aRed   = 0;
    $aGreen = 0;
    $aBlue  = 0;
    $aCount = (count($aMatrix)-1)/2;
    
    for ($i=-$aCount;$i<=$aCount;$i++)
    {
      for ($j=-$aCount;$j<=$aCount;$j++)
      {
        $aRGB = getColorAt($aIm,$aX+$i,$aY+$j,$defaultColor);
        $aRed   += $aRGB["red"]*$aMatrix[$i+$aCount][$j+$aCount];
        $aGreen += $aRGB["green"]*$aMatrix[$i+$aCount][$j+$aCount];
        $aBlue  += $aRGB["blue"]*$aMatrix[$i+$aCount][$j+$aCount];
      }
    }
    
    $aRed   = round($aRed/$aSum);
    $aGreen = round($aGreen/$aSum);
    $aBlue  = round($aBlue/$aSum);
    
    $bRGB = array("red"=>$aRed,"green"=>$aGreen,"blue"=>$aBlue);
    return $bRGB;
  }

  /**
   * Makes the basic image, putting the letters on the background.
   * @param resource The image.
   * @param int      The left and right border.
   * @param int      The top and bottom border.
   * @param int      The distance between two letters.
   * @param int      The string to write.
   * @param int      The directory containing the letter pictures.
   */
  function composeBasicImage($aIm,$aBorder,$bBorder,$lSpacing,$aString,$picDir)
  {
    $aLeft = $aBorder;
    for ($i=0;$i<strlen($aString);$i++)
    {
      $aName = $picDir . $aString[$i] . ".png";
      $bIm = @ImageCreateFromPNG($aName);
      $aSize = getimagesize($aName);
      ImageCopy($aIm,$bIm,$aLeft,$bBorder,0,0,$aSize[0],$aSize[1]);
      $aSize = getimagesize($aName);
      $aLeft += $aSize[0] + $lSpacing; 
    }
  }

  /**
   * Predicts some information about the final picture.
   * @param  string The string to write.
   * @param  int    The left and right border.
   * @param  int    The top and bottom border.
   * @param  int    The distance between two letters.
   * @param  int    The directory containing the letter pictures.
   * @return array  Contains the final width and height of the total image,
   *                width and height of the untreated text as well as the average height of the text.
   */
  function predictImageSize($aString,$xBorder,$yBorder,$lSpacing,$picDir)
  {
    $aWidth  = 0;
    $aHeight = 0;
    $cHeight = 0;
    
    for ($i=0;$i<strlen($aString);$i++)
    {
      $aName = $picDir . $aString[$i] . ".png";
      $aSize = getimagesize($aName);
      $aWidth += $aSize[0]+$lSpacing;
      $cHeight += $aSize[1];
      if ($aSize[1] > $aHeight)
      {
        $aHeight = $aSize[1];
      }
    }
    
    $bWidth  = $aWidth+$xBorder*2;
    $bHeight = $aHeight+$yBorder*2;
    
    return array($bWidth,$bHeight,$aWidth,$aHeight,$cHeight/strlen($aString));
  }

  /**
   * Applies a distortion to the vertical axes.
   * @param resource The original image.
   * @param resource The resulting image.
   * @param int      Width of the text.
   * @param int      Height of the text.
   * @param int      Left position of the text.
   * @param int      Top position of the text.
   * @param float    Minimal vertical distortion.
   * @param float    Random part of the vertical distortion.
   */
  function applyVerticalRoundness($aIm,$bIm,$xText,$yText,$xBorder,$yBorder,$verticalMinimum,$verticalVariance)
  {
    $aStretch = $yText*($verticalMinimum+(rand(0,100)/100)*$verticalVariance);
    if (rand(1,100) > 50)
    {
      $aStretch *= -1;
    }
    $aDelta = 0;
    for ($i=0;$i<$yText;$i=$i+1)
    {
      $aX = $xBorder;
      $aY = $yBorder+$i;
      $aDelta = (2*$i-($yText))/($yText);
      $aDelta = sin(acos($aDelta));
      $aDelta = $aDelta*$aStretch;
      $bX = $aX-$aDelta;
      ImageCopy($bIm,$aIm,$bX,$aY,$aX,$aY,$xText,1);
    }
  }

  /**
   * Stretches the text using a cubic function with randomized parameters.
   * @param resource The original image.
   * @param resource The resulting image.
   * @param int      Width of the image.
   * @param int      Height of the image.
   */
  function applyHorizontalWaveLine($aIm,$bIm,$xSize,$ySize,$yBorder)
  {
    $xInterval = 20;
    $xHalfInterval = $xInterval/2;
    $xWindow   = 14;
    $aLeftMax  = -($xHalfInterval-($xInterval-$xWindow));
    $aLeft     = rand(-$xHalfInterval,$aLeftMax);
    
    $aParam = 0.01 + rand(0,100)/100*.005;
    $bParam = rand(0,100)/100*1.5;
    
    for ($x=0;$x<$xSize;$x++)
    {
      $xP     = $x/$xSize*$xWindow+$aLeft;
      $aDelta = $aParam*pow($xP,3)+$bParam*$xP;
      if ($aDelta > $yBorder)
      {
        $aDelta = $yBorder;
      }
      ImageCopy($bIm,$aIm,$x,$aDelta,$x,0,1,$ySize);
    }
  }

  /**
   * Applies a given matrix on the picture.
   * @param resource The original image.
   * @param resource The resulting image.
   * @param array    The matrix to apply.
   * @param int      The sum of the matrix coefficients.
   * @param int      Width of the picture.
   * @param int      Height of the picture.
   * @param array    Backgroundcolor of the picture.
   */
  function applyMatrix($aIm,$bIm,$aMatrix,$aSum,$xSize,$ySize,$bgColor)
  {
    $defaultRGB = array("red"=>$bgColor["red"],"green"=>$bgColor["green"],"blue"=>$bgColor["blue"]);
    for ($i=0;$i<$xSize;$i++)
    {
      for ($j=0;$j<$ySize;$j++)
      {
        $aRGB = getGaussianAt($aIm,$i,$j,$aMatrix,$aSum,$defaultRGB);
        $aColor = ImageColorAllocate($aIm,$aRGB["red"],$aRGB["green"],$aRGB["blue"]);
        imagesetpixel($bIm,$i,$j,$aColor);
      }
    }
  }

  /**
   * Calculates the coefficient sum of a given matrix.
   * @param  array A two dimensional matrix.
   * @return int   The coefficient sum.
   */
  function getMatrixTotal($aMatrix)
  {
    $aSum = 0;
    for ($i=0;$i<count($aMatrix);$i++)
    {
      for ($j=0;$j<count($aMatrix);$j++)
      {
        $aSum += $aMatrix[$i][$j];
      }
    }
    return $aSum;
  }

  session_start();

  // Setup the parameters of the captcha.
  // Length of the captcha string.
  $aLength          = 6;
  // Left and right border.
  $xBorder          = 20;
  // Top and bottom border.
  $yBorder          = 20;
  // Spacing between the letters.
  $lSpacing         = 0;
  // Minimal distortion of the vertical axis.
  $verticalMinimum  = 0.0;
  // Random distortion part of the vertical axis.
  $verticalVariance = 0.15;
  // The directory containing the letters (a.png, .. , z.png)
  $picDir           = "fonts/verdanaRed/";
  // The background color of the image.
  $bgColor          = array("red"=>170,"green"=>170,"blue"=>170);
  // The color of the guide lines (should be the same as the letters).
  $lineColor        = array("red"=>255,"green"=>0,"blue"=>0);
  // A 3x3 gaussian blur filter.
  $aMatrix = array(array(10,22,10),
                   array(22,75,22),
                   array(10,22,10));
  // The coefficient sum.
  $aSum    = getMatrixTotal($aMatrix);
  
  // Only generate the captcha if empty.
  if (strlen($_SESSION["captcha"]) == 0)
  {
    $_SESSION["captcha"] = getRandomCode($aLength);
  }
  $aString = $_SESSION["captcha"];

  // Predict image dimensions.
  list($xSize,$ySize,$xText,$yText,$avgHeight) = predictImageSize($aString,$xBorder,$yBorder,$lSpacing,$picDir);
  // Create and inizialize image and auxiliary image.
  $aIm = @ImageCreateTrueColor($xSize,$ySize);
  $bIm = @ImageCreateTrueColor($xSize,$ySize);
  $aColor = ImageColorAllocate($aIm,$bgColor["red"],$bgColor["green"],$bgColor["blue"]);
  $bColor = ImageColorAllocate($bIm,$bgColor["red"],$bgColor["green"],$bgColor["blue"]);
  $cColor = ImageColorAllocate($aIm,$lineColor["red"],$lineColor["green"],$lineColor["blue"]);
  ImageFillToBorder($aIm, 0, 0, $aColor, $aColor);
  ImageFillToBorder($bIm, 0, 0, $bColor, $bColor);
  
  // Draw 'guidelines' to make segmentation harder.
  $aY = $yBorder;
  $bY = $yBorder+$avgHeight-1;
  imageline($aIm,$xBorder,$aY,$xBorder+$xSize,$aY,$cColor);
  imageline($aIm,$xBorder,$bY,$xBorder+$xSize,$bY,$cColor);
  
  // Draw the image, apply distortions and gaussian blur.
  composeBasicImage(&$aIm,$xBorder,$yBorder,$lSpacing,$aString,$picDir);
  applyVerticalRoundness(&$aIm,&$bIm,$xText,$yText,$xBorder,$yBorder,$verticalMinimum,$verticalVariance);
  applyHorizontalWaveLine(&$bIm,&$aIm,$xSize,$ySize,$yBorder);
  applyMatrix(&$aIm,&$bIm,$aMatrix,$aSum,$xSize,$ySize,$bgColor);
  
  // Output the image.
  header ("Content-type: image/png");
  ImagePNG ($bIm);
?>