image_captcha.user.inc in CAPTCHA 6

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image_captcha/image_captcha.user.inc

<?php

/**
 * Implementation of image CAPTCHA for use with the CAPTCHA module
 *
 * Loosely Based on MyCaptcha by Heine Deelstra
 * (http://heine.familiedeelstra.com/mycaptcha-download)
 */

/**
 * menu callback function that generates the CAPTCHA image
 */
function image_captcha_image($seed = NULL) {
  if (!$seed) {
    return;
  }

  // Only generate captcha if code exists in the session.
  if (isset($_SESSION['image_captcha'][$seed])) {
    $code = $_SESSION['image_captcha'][$seed];

    // Unset the code from $_SESSION to prevent rerendering the CAPTCHA.
    unset($_SESSION['image_captcha'][$seed]);

    // generate the image
    $image = @_image_captcha_generate_image($code);

    // check of generation was successful
    if (!$image) {
      watchdog('CAPTCHA', 'Generation of image CAPTCHA failed. Check your image CAPTCHA configuration and especially the used font.', array(), WATCHDOG_ERROR);
      exit;
    }

    // Send the image resource as an image to the client
    drupal_set_header("Content-type: image/jpeg");

    // Following header is needed for Konqueror, which would re-request the image
    // on a mouseover event, which failes because the image can only be generated
    // once. This cache directive forces Konqueror to use cache instead of
    // re-requesting
    drupal_set_header("Cache-Control: max-age=3600, must-revalidate");

    // print the image as jpg to the client
    imagejpeg($image);

    // Clean up
    imagedestroy($image);
    exit;
  }
}

/**
 * small helper function for parsing a hexadecimal color to a RGB tuple
 */
function _image_captcha_hex_to_rgb($hex) {

  // handle #RGB format
  if (strlen($hex) == 4) {
    $hex = $hex[1] . $hex[1] . $hex[2] . $hex[2] . $hex[3] . $hex[3];
  }
  $c = hexdec($hex);
  $rgb = array();
  for ($i = 16; $i >= 0; $i -= 8) {
    $rgb[] = $c >> $i & 0xff;
  }
  return $rgb;
}

/**
 * base function for generating a image CAPTCHA
 */
function _image_captcha_generate_image($code) {

  // get font
  list($font, $errmsg, $errvar) = _image_captcha_get_font();
  if (!$font) {
    watchdog('CAPTCHA', $errmsg, $errvar, WATCHDOG_ERROR);
    exit;
  }

  // get other settings
  $font_size = (int) variable_get('image_captcha_font_size', 30);
  $character_spacing = (double) variable_get('image_captcha_character_spacing', '1.2');
  $characters = _image_captcha_utf8_split($code);
  $character_quantity = count($characters);
  $width = $character_spacing * $font_size * $character_quantity;
  $height = 2 * $font_size;

  // create image resource
  $image = imagecreatetruecolor($width, $height);
  if (!$image) {
    return FALSE;
  }

  // get background color and paint
  $background_rgb = _image_captcha_hex_to_rgb(variable_get('image_captcha_background_color', '#ffffff'));
  $background_color = imagecolorallocate($image, $background_rgb[0], $background_rgb[1], $background_rgb[2]);
  imagefilledrectangle($image, 0, 0, $width, $height, $background_color);

  // draw text
  if (variable_get('image_captcha_double_vision', 0)) {
    $result = _image_captcha_image_generator_print_string($image, $width, $height, $font, $font_size, $code, TRUE);
    if (!$result) {
      return FALSE;
    }
  }
  $result = _image_captcha_image_generator_print_string($image, $width, $height, $font, $font_size, $code, FALSE);
  if (!$result) {
    return FALSE;
  }

  // add noise
  $noise_colors = array();
  for ($i = 0; $i < 20; $i++) {
    $noise_colors[] = imagecolorallocate($image, mt_rand(0, 255), mt_rand(0, 255), mt_rand(0, 255));
  }

  // Add additional noise.
  if (variable_get('image_captcha_dot_noise', 0)) {
    _image_captcha_image_generator_add_dots($image, $width, $height, $noise_colors);
  }
  if (variable_get('image_captcha_line_noise', 0)) {
    _image_captcha_image_generator_add_lines($image, $width, $height, $noise_colors);
  }

  // Distort the image.
  $distortion_amplitude = 0.25 * $font_size * variable_get('image_captcha_distortion_amplitude', 6) / 10.0;
  if ($distortion_amplitude > 1) {

    // distortion parameters
    $wavelength_xr = (2 + 3 * lcg_value()) * $font_size;
    $wavelength_yr = (2 + 3 * lcg_value()) * $font_size;
    $freq_xr = 2 * 3.141592 / $wavelength_xr;
    $freq_yr = 2 * 3.141592 / $wavelength_yr;
    $wavelength_xt = (2 + 3 * lcg_value()) * $font_size;
    $wavelength_yt = (2 + 3 * lcg_value()) * $font_size;
    $freq_xt = 2 * 3.141592 / $wavelength_xt;
    $freq_yt = 2 * 3.141592 / $wavelength_yt;
    $distorted_image = imagecreatetruecolor($width, $height);
    if (!$distorted_image) {
      return FALSE;
    }
    if (variable_get('image_captcha_bilinair_interpolation', FALSE)) {

      // distortion with bilinear interpolation
      for ($x = 0; $x < $width; $x++) {
        for ($y = 0; $y < $height; $y++) {

          // get distorted sample point in source image
          $r = $distortion_amplitude * sin($x * $freq_xr + $y * $freq_yr);
          $theta = $x * $freq_xt + $y * $freq_yt;
          $sx = $x + $r * cos($theta);
          $sy = $y + $r * sin($theta);
          $sxf = (int) floor($sx);
          $syf = (int) floor($sy);
          if ($sxf < 0 || $syf < 0 || $sxf >= $width - 1 || $syf >= $height - 1) {
            $color = $background_color;
          }
          else {

            // bilinear interpolation: sample at four corners
            $color_00 = imagecolorat($image, $sxf, $syf);
            $color_00_r = $color_00 >> 16 & 0xff;
            $color_00_g = $color_00 >> 8 & 0xff;
            $color_00_b = $color_00 & 0xff;
            $color_10 = imagecolorat($image, $sxf + 1, $syf);
            $color_10_r = $color_10 >> 16 & 0xff;
            $color_10_g = $color_10 >> 8 & 0xff;
            $color_10_b = $color_10 & 0xff;
            $color_01 = imagecolorat($image, $sxf, $syf + 1);
            $color_01_r = $color_01 >> 16 & 0xff;
            $color_01_g = $color_01 >> 8 & 0xff;
            $color_01_b = $color_01 & 0xff;
            $color_11 = imagecolorat($image, $sxf + 1, $syf + 1);
            $color_11_r = $color_11 >> 16 & 0xff;
            $color_11_g = $color_11 >> 8 & 0xff;
            $color_11_b = $color_11 & 0xff;

            // interpolation factors
            $u = $sx - $sxf;
            $v = $sy - $syf;

            // interpolate
            $r = (int) ((1 - $v) * ((1 - $u) * $color_00_r + $u * $color_10_r) + $v * ((1 - $u) * $color_01_r + $u * $color_11_r));
            $g = (int) ((1 - $v) * ((1 - $u) * $color_00_g + $u * $color_10_g) + $v * ((1 - $u) * $color_01_g + $u * $color_11_g));
            $b = (int) ((1 - $v) * ((1 - $u) * $color_00_b + $u * $color_10_b) + $v * ((1 - $u) * $color_01_b + $u * $color_11_b));

            // build color
            $color = ($r << 16) + ($g << 8) + $b;
          }
          imagesetpixel($distorted_image, $x, $y, $color);
        }
      }
    }
    else {

      // distortion with nearest neighbor interpolation
      for ($x = 0; $x < $width; $x++) {
        for ($y = 0; $y < $height; $y++) {

          // get distorted sample point in source image
          $r = $distortion_amplitude * sin($x * $freq_xr + $y * $freq_yr);
          $theta = $x * $freq_xt + $y * $freq_yt;
          $sx = $x + $r * cos($theta);
          $sy = $y + $r * sin($theta);
          $sxf = (int) floor($sx);
          $syf = (int) floor($sy);
          if ($sxf < 0 || $syf < 0 || $sxf >= $width - 1 || $syf >= $height - 1) {
            $color = $background_color;
          }
          else {
            $color = imagecolorat($image, $sxf, $syf);
          }
          imagesetpixel($distorted_image, $x, $y, $color);
        }
      }
    }

    // release undistorted image
    imagedestroy($image);

    // return distorted image
    return $distorted_image;
  }
  else {
    return $image;
  }
}
function _image_captcha_image_generator_add_lines(&$image, $width, $height, $colors) {
  $line_quantity = $width * $height / 200.0 * (int) variable_get('image_captcha_noise_level', 5) / 10.0;
  for ($i = 0; $i < $line_quantity; $i++) {
    imageline($image, mt_rand(0, $width), mt_rand(0, $height), mt_rand(0, $width), mt_rand(0, $height), $colors[array_rand($colors)]);
  }
}
function _image_captcha_image_generator_add_dots(&$image, $width, $height, $colors) {
  $noise_quantity = $width * $height / 2.0 * (int) variable_get('image_captcha_noise_level', 5) / 10.0;
  for ($i = 0; $i < $noise_quantity; $i++) {
    imagesetpixel($image, mt_rand(0, $width), mt_rand(0, $height), $colors[array_rand($colors)]);
  }
}

/**
 * Helper function for drawing text on the image
 *
 * @param $background_mode if the text is for the background of the double vision mode
 */
function _image_captcha_image_generator_print_string(&$image, $width, $height, $font, $font_size, $text, $background_mode = FALSE) {

  // get characters
  $characters = _image_captcha_utf8_split($text);
  $character_quantity = count($characters);

  // get character width for builtin font
  if ($font == 'BUILTIN') {
    $character_width = imagefontwidth(5);
    $character_height = imagefontheight(5);
    $bbox = array(
      0,
      $character_height,
      $character_width,
      $character_height,
      $character_width,
      0,
      0,
      0,
    );
  }

  // get colors
  $background_rgb = _image_captcha_hex_to_rgb(variable_get('image_captcha_background_color', '#ffffff'));
  $foreground_rgb = _image_captcha_hex_to_rgb(variable_get('image_captcha_foreground_color', '#000000'));

  // correct foreground for background mode (double vision)
  if ($background_mode) {
    for ($i = 0; $i < 3; $i++) {
      $foreground_rgb[$i] = 0.75 * $background_rgb[$i] + 0.25 * $foreground_rgb[$i];
    }
  }
  $background_color = imagecolorallocate($image, $background_rgb[0], $background_rgb[1], $background_rgb[2]);
  $foreground_color = imagecolorallocate($image, $foreground_rgb[0], $foreground_rgb[1], $foreground_rgb[2]);

  // precalculate the value ranges for color randomness
  $foreground_randomness = (int) variable_get('image_captcha_foreground_color_randomness', 100);
  if ($foreground_randomness) {
    if ($background_mode) {
      $foreground_randomness *= 0.25;
    }
    $foreground_color_range = array();
    for ($i = 0; $i < 3; $i++) {
      $foreground_color_range[$i] = array(
        max(0, $foreground_rgb[$i] - $foreground_randomness),
        min(255, $foreground_rgb[$i] + $foreground_randomness),
      );
    }
  }

  // set default text color
  $color = $foreground_color;

  // the image is seperated in different character cages, one for each character
  // each character will be somewhere inside that cage
  $ccage_width = $width / $character_quantity;
  $ccage_height = $height;
  foreach ($characters as $c => $character) {

    // initial position of character: in the center of its cage
    $center_x = ($c + 0.5) * $ccage_width;
    $center_y = 0.5 * $height;

    // get character dimensions for ttf fonts
    if ($font != 'BUILTIN') {
      $bbox = imagettfbbox($font_size, 0, realpath($font), $character);
    }

    // determine print position: at what coordinate should the character be
    // printed so that the bounding box would be nicely centered in the cage?
    $pos_x = $center_x - 0.5 * ($bbox[0] + $bbox[2]);
    $pos_y = $center_y - 0.5 * ($bbox[1] + $bbox[7]);

    // calculate available room to jitter: how much can the character be moved
    // so that it stays inside its cage?
    $dev_x = 0.5 * max(0, $ccage_width - ($bbox[2] - $bbox[0]));
    $dev_y = 0.5 * max(0, $ccage_height - ($bbox[1] - $bbox[7]));

    // add jitter to position
    $pos_x = $pos_x + mt_rand(-$dev_x, $dev_x);
    $pos_y = $pos_y + mt_rand(-$dev_y, $dev_y);

    // calculate text color in case of randomness
    if ($foreground_randomness) {
      $color = imagecolorallocate($image, mt_rand($foreground_color_range[0][0], $foreground_color_range[0][1]), mt_rand($foreground_color_range[1][0], $foreground_color_range[1][1]), mt_rand($foreground_color_range[2][0], $foreground_color_range[2][1]));
    }

    // draw character
    if ($font == 'BUILTIN') {
      imagestring($image, 5, $pos_x, $pos_y, $character, $color);
    }
    else {
      imagettftext($image, $font_size, 0, $pos_x, $pos_y, $color, realpath($font), $character);
    }

    // for debugging purposes: draw character bounding box
    // imagerectangle($image, $pos_x + $bbox[0], $pos_y + $bbox[1], $pos_x + $bbox[2], $pos_y + $bbox[7], $color);
  }

  // return a sign of success
  return TRUE;
}

Functions

Name	Description
image_captcha_image	menu callback function that generates the CAPTCHA image
_image_captcha_generate_image	base function for generating a image CAPTCHA
_image_captcha_hex_to_rgb	small helper function for parsing a hexadecimal color to a RGB tuple
_image_captcha_image_generator_add_dots
_image_captcha_image_generator_add_lines
_image_captcha_image_generator_print_string	Helper function for drawing text on the image