CodeIgniter 驗證碼輔助函數 源代碼分析

if ( ! function_exists('create_captcha'))
{
	function create_captcha($data = '', $img_path = '', $img_url = '', $font_path = '')
	{
		$defaults = array('word' => '', 'img_path' => '', 'img_url' => '', 'img_width' => '150', 'img_height' => '30', 'font_path' => '', 'expiration' => 7200);

		// 初始化驗證碼的參數
		foreach ($defaults as $key => $val)
		{
			if ( ! is_array($data))
			{
				if ( ! isset($$key) OR $$key == '')
				{
					$$key = $val;
				}
			}
			else
			{
				$$key = ( ! isset($data[$key])) ? $val : $data[$key];
			}
		}

		// 如果圖像保存路徑或圖像鏈接爲空，則返回FALSE
		if ($img_path == '' OR $img_url == '')
		{
			return FALSE;
		}

		// 如果圖像保存路徑不爲目錄返回FALSE
		if ( ! @is_dir($img_path))
		{
			return FALSE;
		}

		// 如果圖像路徑不可寫返回FALSE
		if ( ! is_writable($img_path))
		{
			return FALSE;
		}

		// 檢查gd庫是否加載，未加載返回FALSE
		if ( ! extension_loaded('gd'))
		{
			return FALSE;
		}

		// -----------------------------------
		// Remove old images
		// -----------------------------------
		
		// 獲取當前時間的微秒數和秒數
		list($usec, $sec) = explode(" ", microtime());
		$now = ((float)$usec + (float)$sec);

		// 打開圖像存儲路徑目錄的句柄
		$current_dir = @opendir($img_path);

		// 遍歷目錄中所有文件，若文件名+過期時間小於當前時間，則說明已過期，刪除該文件（驗證碼文件名爲上面變量$now）
		while ($filename = @readdir($current_dir))
		{
			if ($filename != "." and $filename != ".." and $filename != "index.html")
			{
				$name = str_replace(".jpg", "", $filename);

				if (($name + $expiration) < $now)
				{
					@unlink($img_path.$filename);
				}
			}
		}

		@closedir($current_dir);

		// -----------------------------------
		// Do we have a "word" yet?
		// -----------------------------------
		// 如果未指定$word，默認的word爲數字+小寫字母+大寫字母，並取隨機的8個字符
	   if ($word == '')
	   {
			$pool = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';

			$str = '';
			for ($i = 0; $i < 8; $i++)
			{
				$str .= substr($pool, mt_rand(0, strlen($pool) -1), 1);
			}

			$word = $str;
	   }

		// -----------------------------------
		// Determine angle and position
		// -----------------------------------
		// 設置字體角度和位置
		$length	= strlen($word);
		$angle	= ($length >= 6) ? rand(-($length-6), ($length-6)) : 0;
		$x_axis	= rand(6, (360/$length)-16);
		$y_axis = ($angle >= 0 ) ? rand($img_height, $img_width) : rand(6, $img_height);

		// -----------------------------------
		// Create image
		// -----------------------------------

		// PHP.net recommends imagecreatetruecolor(), but it isn't always available
		// 創建一個寬度爲img_width高度爲img_height的真彩色圖像
		if (function_exists('imagecreatetruecolor'))
		{
			$im = imagecreatetruecolor($img_width, $img_height);
		}
		else
		{
			$im = imagecreate($img_width, $img_height);
		}

		// -----------------------------------
		//  Assign colors
		// -----------------------------------
		// 指定一些顏色，背景色，邊框色，字體顏色，螺旋線顏色，陰影色
		$bg_color		= imagecolorallocate ($im, 255, 255, 255);
		$border_color	= imagecolorallocate ($im, 153, 102, 102);
		$text_color		= imagecolorallocate ($im, 204, 153, 153);
		$grid_color		= imagecolorallocate($im, 255, 182, 182);
		$shadow_color	= imagecolorallocate($im, 255, 240, 240);

		// -----------------------------------
		//  Create the rectangle
		// -----------------------------------
		// 畫一個矩形並用bg_color填充
		ImageFilledRectangle($im, 0, 0, $img_width, $img_height, $bg_color);

		// -----------------------------------
		//  Create the spiral pattern
		// -----------------------------------

		// 創建螺旋圖樣
		$theta		= 1;
		$thetac		= 7;
		$radius		= 16;
		$circles	= 20;
		$points		= 32;

		for ($i = 0; $i < ($circles * $points) - 1; $i++)
		{
			$theta = $theta + $thetac;
			$rad = $radius * ($i / $points );
			$x = ($rad * cos($theta)) + $x_axis;
			$y = ($rad * sin($theta)) + $y_axis;
			$theta = $theta + $thetac;
			$rad1 = $radius * (($i + 1) / $points);
			$x1 = ($rad1 * cos($theta)) + $x_axis;
			$y1 = ($rad1 * sin($theta )) + $y_axis;
			imageline($im, $x, $y, $x1, $y1, $grid_color);
			$theta = $theta - $thetac;
		}

		// -----------------------------------
		//  Write the text
		// -----------------------------------
		// 用imagettftext函數寫入隨機字符串
		$use_font = ($font_path != '' AND file_exists($font_path) AND function_exists('imagettftext')) ? TRUE : FALSE;

		if ($use_font == FALSE)
		{
			$font_size = 5;
			$x = rand(0, $img_width/($length/3));
			$y = 0;
		}
		else
		{
			$font_size	= 16;
			$x = rand(0, $img_width/($length/1.5));
			$y = $font_size+2;
		}

		for ($i = 0; $i < strlen($word); $i++)
		{
			if ($use_font == FALSE)
			{
				$y = rand(0 , $img_height/2);
				imagestring($im, $font_size, $x, $y, substr($word, $i, 1), $text_color);
				$x += ($font_size*2);
			}
			else
			{
				$y = rand($img_height/2, $img_height-3);
				imagettftext($im, $font_size, $angle, $x, $y, $text_color, $font_path, substr($word, $i, 1));
				$x += $font_size;
			}
		}


		// -----------------------------------
		//  Create the border
		// -----------------------------------
		// 創建字符串邊框
		imagerectangle($im, 0, 0, $img_width-1, $img_height-1, $border_color);

		// -----------------------------------
		//  Generate the image
		// -----------------------------------

		// 生成jpeg圖像和圖像鏈接
		$img_name = $now.'.jpg';

		ImageJPEG($im, $img_path.$img_name);

		$img = "<img src=\"$img_url$img_name\" width=\"$img_width\" height=\"$img_height\" style=\"border:0;\" alt=\" \" />";

		ImageDestroy($im);

		return array('word' => $word, 'time' => $now, 'image' => $img);
	}
}