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<?php
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/**
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* @file
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* Functions for the generation of the CAPTCHA image.
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*
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* Loosely Based on MyCaptcha by Heine Deelstra
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* (http://heine.familiedeelstra.com/mycaptcha-download)
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*/
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/**
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* Menu callback function that generates the CAPTCHA image.
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*/
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function image_captcha_image() {
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// If output buffering is on: discard current content and disable further buffering
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if (ob_get_level()) {
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ob_end_clean();
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}
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if (!isset($_GET['sid'])) {
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exit();
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}
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$captcha_sid = $_GET['sid'];
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// Get solution (the code to show).
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$code = db_query("SELECT solution FROM {captcha_sessions} WHERE csid = :csid",
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array(':csid' => $captcha_sid)
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)->fetchField();
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// Only generate captcha if code exists in the session.
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if ($code !== FALSE) {
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// generate the image
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$image = @_image_captcha_generate_image($code);
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// check of generation was successful
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if (!$image) {
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watchdog('CAPTCHA', 'Generation of image CAPTCHA failed. Check your image CAPTCHA configuration and especially the used font.', array(), WATCHDOG_ERROR);
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exit();
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}
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// Send the image resource as an image file to the client.
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$file_format = variable_get('image_captcha_file_format', IMAGE_CAPTCHA_FILE_FORMAT_JPG);
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if ($file_format == IMAGE_CAPTCHA_FILE_FORMAT_JPG) {
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drupal_add_http_header('Content-Type', 'image/jpeg');
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imagejpeg($image);
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}
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else {
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drupal_add_http_header('Content-Type', 'image/png');
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imagepng($image);
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}
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// Clean up the image resource.
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imagedestroy($image);
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}
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exit();
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}
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/**
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* Small helper function for parsing a hexadecimal color to a RGB tuple.
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*/
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function _image_captcha_hex_to_rgb($hex) {
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// handle #RGB format
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if (strlen($hex) == 4) {
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$hex = $hex[1] . $hex[1] . $hex[2] . $hex[2] . $hex[3] . $hex[3];
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}
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$c = hexdec($hex);
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$rgb = array();
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for ($i = 16; $i >= 0; $i -= 8) {
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$rgb[] = ($c >> $i) & 0xFF;
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}
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return $rgb;
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}
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/**
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* Base function for generating a image CAPTCHA.
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*/
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function _image_captcha_generate_image($code) {
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// Get font.
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$fonts = _image_captcha_get_enabled_fonts();
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// get other settings
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$font_size = (int) variable_get('image_captcha_font_size', 30);
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list($width, $height) = _image_captcha_image_size($code);
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// create image resource
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$image = imagecreatetruecolor($width, $height);
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if (!$image) {
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return FALSE;
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}
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// Get the background color and paint the background.
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$background_rgb = _image_captcha_hex_to_rgb(variable_get('image_captcha_background_color', '#ffffff'));
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$background_color = imagecolorallocate($image, $background_rgb[0], $background_rgb[1], $background_rgb[2]);
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// Set transparency if needed.
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$file_format = variable_get('image_captcha_file_format', IMAGE_CAPTCHA_FILE_FORMAT_JPG);
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if ($file_format == IMAGE_CAPTCHA_FILE_FORMAT_TRANSPARENT_PNG) {
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imagecolortransparent($image, $background_color);
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}
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imagefilledrectangle($image, 0, 0, $width, $height, $background_color);
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// Do we need to draw in RTL mode?
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global $language;
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$rtl = $language->direction && ((bool) variable_get('image_captcha_rtl_support', 0));
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// draw text
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$result = _image_captcha_image_generator_print_string($image, $width, $height, $fonts, $font_size, $code, $rtl);
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if (!$result) {
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return FALSE;
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}
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// add noise
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$noise_colors = array();
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for ($i = 0; $i < 20; $i++) {
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$noise_colors[] = imagecolorallocate($image, mt_rand(0, 255), mt_rand(0, 255), mt_rand(0, 255));
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}
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// Add additional noise.
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if (variable_get('image_captcha_dot_noise', 0)) {
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_image_captcha_image_generator_add_dots($image, $width, $height, $noise_colors);
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}
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if (variable_get('image_captcha_line_noise', 0)) {
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_image_captcha_image_generator_add_lines($image, $width, $height, $noise_colors);
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}
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// Distort the image.
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$distortion_amplitude = .25 * $font_size * variable_get('image_captcha_distortion_amplitude', 0) / 10.0;
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if ($distortion_amplitude > 1) {
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// distortion parameters
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$wavelength_xr = (2+3*lcg_value())*$font_size;
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$wavelength_yr = (2+3*lcg_value())*$font_size;
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$freq_xr = 2 * 3.141592 / $wavelength_xr;
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$freq_yr = 2 * 3.141592 / $wavelength_yr;
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$wavelength_xt = (2+3*lcg_value())*$font_size;
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$wavelength_yt = (2+3*lcg_value())*$font_size;
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$freq_xt = 2 * 3.141592 / $wavelength_xt;
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$freq_yt = 2 * 3.141592 / $wavelength_yt;
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$distorted_image = imagecreatetruecolor($width, $height);
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if ($file_format == IMAGE_CAPTCHA_FILE_FORMAT_TRANSPARENT_PNG) {
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imagecolortransparent($distorted_image, $background_color);
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}
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if (!$distorted_image) {
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return FALSE;
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}
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if (variable_get('image_captcha_bilinear_interpolation', FALSE)) {
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// distortion with bilinear interpolation
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for ($x = 0; $x < $width; $x++) {
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for ($y = 0; $y < $height; $y++) {
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// get distorted sample point in source image
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$r = $distortion_amplitude * sin($x * $freq_xr + $y * $freq_yr);
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$theta = $x * $freq_xt + $y * $freq_yt;
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$sx = $x + $r * cos($theta);
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$sy = $y + $r * sin($theta);
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$sxf = (int)floor($sx);
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$syf = (int)floor($sy);
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if ($sxf < 0 || $syf < 0 || $sxf >= $width - 1 || $syf >= $height - 1) {
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$color = $background_color;
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}
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else {
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// bilinear interpolation: sample at four corners
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$color_00 = imagecolorat($image, $sxf , $syf );
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$color_00_r = ($color_00 >> 16) & 0xFF;
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$color_00_g = ($color_00 >> 8) & 0xFF;
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$color_00_b = $color_00 & 0xFF;
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$color_10 = imagecolorat($image, $sxf+1, $syf );
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$color_10_r = ($color_10 >> 16) & 0xFF;
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$color_10_g = ($color_10 >> 8) & 0xFF;
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$color_10_b = $color_10 & 0xFF;
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$color_01 = imagecolorat($image, $sxf , $syf+1);
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$color_01_r = ($color_01 >> 16) & 0xFF;
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$color_01_g = ($color_01 >> 8) & 0xFF;
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$color_01_b = $color_01 & 0xFF;
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$color_11 = imagecolorat($image, $sxf+1, $syf+1);
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$color_11_r = ($color_11 >> 16) & 0xFF;
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$color_11_g = ($color_11 >> 8) & 0xFF;
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$color_11_b = $color_11 & 0xFF;
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// interpolation factors
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$u = $sx - $sxf;
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$v = $sy - $syf;
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// interpolate
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$r = (int)((1-$v)*((1-$u)*$color_00_r + $u*$color_10_r) + $v*((1-$u)*$color_01_r + $u*$color_11_r));
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$g = (int)((1-$v)*((1-$u)*$color_00_g + $u*$color_10_g) + $v*((1-$u)*$color_01_g + $u*$color_11_g));
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$b = (int)((1-$v)*((1-$u)*$color_00_b + $u*$color_10_b) + $v*((1-$u)*$color_01_b + $u*$color_11_b));
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// build color
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$color = ($r<<16) + ($g<<8) + $b;
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}
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imagesetpixel($distorted_image, $x, $y, $color);
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}
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}
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}
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else {
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// distortion with nearest neighbor interpolation
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for ($x = 0; $x < $width; $x++) {
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for ($y = 0; $y < $height; $y++) {
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// get distorted sample point in source image
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$r = $distortion_amplitude * sin($x * $freq_xr + $y * $freq_yr);
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$theta = $x * $freq_xt + $y * $freq_yt;
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$sx = $x + $r * cos($theta);
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$sy = $y + $r * sin($theta);
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$sxf = (int)floor($sx);
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$syf = (int)floor($sy);
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if ($sxf < 0 || $syf < 0 || $sxf >= $width - 1 || $syf >= $height - 1) {
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$color = $background_color;
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}
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else {
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$color = imagecolorat($image, $sxf, $syf);
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}
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imagesetpixel($distorted_image, $x, $y, $color);
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}
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}
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}
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// release undistorted image
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imagedestroy($image);
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// return distorted image
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return $distorted_image;
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}
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else {
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return $image;
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}
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}
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function _image_captcha_image_generator_add_lines(&$image, $width, $height, $colors) {
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$line_quantity = $width * $height/200.0 * ((int) variable_get('image_captcha_noise_level', 5)) / 10.0;
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for ($i = 0; $i < $line_quantity; $i++) {
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imageline($image, mt_rand(0, $width), mt_rand(0, $height), mt_rand(0, $width), mt_rand(0, $height), $colors[array_rand($colors)]);
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}
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}
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function _image_captcha_image_generator_add_dots(&$image, $width, $height, $colors) {
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$noise_quantity = $width * $height * ((int) variable_get('image_captcha_noise_level', 5)) / 10.0;
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for ($i = 0; $i < $noise_quantity; $i++ ) {
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imagesetpixel($image, mt_rand(0, $width), mt_rand(0, $height), $colors[array_rand($colors)]);
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}
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}
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/**
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* Helper function for drawing text on the image.
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*/
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function _image_captcha_image_generator_print_string(&$image, $width, $height, $fonts, $font_size, $text, $rtl=FALSE) {
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// get characters
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$characters = _image_captcha_utf8_split($text);
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$character_quantity = count($characters);
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// get colors
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$background_rgb = _image_captcha_hex_to_rgb(variable_get('image_captcha_background_color', '#ffffff'));
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$foreground_rgb = _image_captcha_hex_to_rgb(variable_get('image_captcha_foreground_color', '#000000'));
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$background_color = imagecolorallocate($image, $background_rgb[0], $background_rgb[1], $background_rgb[2]);
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$foreground_color = imagecolorallocate($image, $foreground_rgb[0], $foreground_rgb[1], $foreground_rgb[2]);
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// precalculate the value ranges for color randomness
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$foreground_randomness = (int)(variable_get('image_captcha_foreground_color_randomness', 100));
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if ($foreground_randomness) {
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$foreground_color_range = array();
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for ($i=0; $i<3; $i++) {
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$foreground_color_range[$i] = array(max(0, $foreground_rgb[$i] - $foreground_randomness), min(255, $foreground_rgb[$i] + $foreground_randomness));
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}
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}
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// set default text color
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$color = $foreground_color;
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// the image is seperated in different character cages, one for each character
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// each character will be somewhere inside that cage
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$ccage_width = $width / $character_quantity;
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$ccage_height = $height;
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foreach ($characters as $c => $character) {
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// initial position of character: in the center of its cage
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$center_x = ($c + 0.5) * $ccage_width;
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if ($rtl) {
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$center_x = $width - $center_x;
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}
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$center_y = 0.5 * $height;
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// Pick a random font from the list.
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$font = $fonts[array_rand($fonts)];
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// Get character dimensions for TrueType fonts.
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if ($font != 'BUILTIN') {
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$bbox = imagettfbbox($font_size, 0, drupal_realpath($font), $character);
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// In very rare cases with some versions of the GD library, the x-value
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// of the left side of the bounding box as returned by the first call of
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// imagettfbbox is corrupt (value -2147483648 = 0x80000000).
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// The weird thing is that calling the function a second time
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// can be used as workaround.
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// This issue is discussed at http://drupal.org/node/349218.
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if ($bbox[2] < 0) {
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$bbox = imagettfbbox($font_size, 0, drupal_realpath($font), $character);
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}
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}
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else {
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$character_width = imagefontwidth(5);
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$character_height = imagefontheight(5);
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$bbox = array(0, $character_height, $character_width, $character_height, $character_width, 0, 0, 0);
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}
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// Random (but small) rotation of the character.
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// TODO: add a setting for this?
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$angle = mt_rand(-10, 10);
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// Determine print position: at what coordinate should the character be
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// printed so that the bounding box would be nicely centered in the cage?
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$bb_center_x = .5 * ($bbox[0] + $bbox[2]);
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$bb_center_y = .5 * ($bbox[1] + $bbox[7]);
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$angle_cos = cos($angle*3.1415/180);
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$angle_sin = sin($angle*3.1415/180);
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$pos_x = $center_x - ($angle_cos * $bb_center_x + $angle_sin * $bb_center_y);
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$pos_y = $center_y - (-$angle_sin * $bb_center_x + $angle_cos * $bb_center_y);
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// Calculate available room to jitter: how much can the character be moved
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// so that it stays inside its cage?
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$bb_width = $bbox[2] - $bbox[0];
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$bb_height = $bbox[1] - $bbox[7];
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$dev_x = .5 * max(0, $ccage_width - abs($angle_cos) * $bb_width - abs($angle_sin) * $bb_height);
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$dev_y = .5 * max(0, $ccage_height - abs($angle_cos) * $bb_height - abs($angle_sin) * $bb_width);
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// add jitter to position
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$pos_x = $pos_x + mt_rand(-$dev_x, $dev_x);
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$pos_y = $pos_y + mt_rand(-$dev_y, $dev_y);
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// calculate text color in case of randomness
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if ($foreground_randomness) {
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$color = imagecolorallocate($image,
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mt_rand($foreground_color_range[0][0], $foreground_color_range[0][1]),
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mt_rand($foreground_color_range[1][0], $foreground_color_range[1][1]),
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mt_rand($foreground_color_range[2][0], $foreground_color_range[2][1])
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);
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}
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// draw character
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if ($font == 'BUILTIN') {
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imagestring($image, 5, $pos_x, $pos_y, $character, $color);
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}
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else {
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imagettftext($image, $font_size, $angle, $pos_x, $pos_y, $color, drupal_realpath($font), $character);
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}
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// For debugging purposes: draw character bounding box (only valid when rotation is disabled).
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// imagerectangle($image, $pos_x + $bbox[0], $pos_y + $bbox[1], $pos_x + $bbox[2], $pos_y + $bbox[7], $color);
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}
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// return a sign of success
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return TRUE;
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}
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