PHP仿GD打开BMP图片

/**
 * 類似GD庫打開圖片, 打開bmp格式圖片
 * $file : 圖片路徑
*/
function imagecreatefrombmp($file)
{
	global $CurrentBit, $echoMode;
	$f = fopen($file,"r");
	$Header = fread($f,2);
	if($Header == "BM")
	{
		$Size = freaddword($f);
		$Reserved1 = freadword($f);
		$Reserved2 = freadword($f);
		$FirstByteOfImage = freaddword($f);
		$SizeBITMAPINFOHEADER = freaddword($f);
		$Width = freaddword($f);
		$Height = freaddword($f);
		$biPlanes = freadword($f);
		$biBitCount = freadword($f);
		$RLECompression = freaddword($f);
		$WidthxHeight = freaddword($f);
		$biXPelsPerMeter = freaddword($f);
		$biYPelsPerMeter = freaddword($f);
		$NumberOfPalettesUsed = freaddword($f);
		$NumberOfImportantColors = freaddword($f);
		if($biBitCount < 24)
		{
			$img = imagecreate($Width, $Height);
			$Colors = pow(2, $biBitCount);
			for($p=0; $p<$Colors; $p++)
			{
				$B = freadbyte($f);
				$G = freadbyte($f);
				$R = freadbyte($f);
				$Reserved = freadbyte($f);
				$Palette[] = imagecolorallocate($img, $R, $G, $B);
			}
			if($RLECompression == 0)
			{
				$Zbytek = (4-ceil(($Width/(8/$biBitCount)))%4)%4;
				for($y=$Height-1; $y>=0; $y--)
				{
					$CurrentBit = 0;
					for($x=0; $x<$Width; $x++)
					{
						$C = freadbits($f, $biBitCount);
						imagesetpixel($img, $x, $y, $Palette[$C]);
					}
					if($CurrentBit != 0)
					{
						freadbyte($f);
					}
					for($g=0; $g<$Zbytek; $g++)
					{
						freadbyte($f);
					}
				}
			}
		}
		if($RLECompression == 1) //$BI_RLE8
		{
			$y = $Height;
			$pocetb = 0;
			while(true)
			{
				$y--;
				$prefix = freadbyte($f);
				$suffix = freadbyte($f);
				$pocetb += 2;
				$echoit = false;
				if($echoit)
				{
					echo "Prefix: $prefix Suffix: $suffix<BR>";
				}
				if(($prefix == 0) && ($suffix == 1))
				{
					break;
				}
				if(feof($f))
				{
					break;
				}
				while(!(($prefix == 0) && ($suffix == 0)))
				{
					if($prefix==0)
					{
						$pocet = $suffix;
						$Data .= fread($f,$pocet);
						$pocetb += $pocet;
						if($pocetb%2 == 1)
						{
							freadbyte($f);
							$pocetb++;
						}
					}
					if($prefix > 0)
					{
						$pocet = $prefix;
						for($r=0; $r<$pocet; $r++)
						{
							$Data.=chr($suffix);
						}
					}
					$prefix = freadbyte($f);
					$suffix = freadbyte($f);
					$pocetb += 2;
					if($echoit)
					{
						echo "Prefix: $prefix Suffix: $suffix<BR>";
					}
				}
				for($x=0; $x<strlen($Data); $x++)
				{
					imagesetpixel($img,$x,$y,$Palette[ord($Data[$x])]);
				}
				$Data="";
			}
		}
		if($RLECompression == 2)
		{
			$y = $Height;
			$pocetb = 0;
			while(true)
			{
				$y--;
				$prefix = freadbyte($f);
				$suffix = freadbyte($f);
				$pocetb += 2;
				$echoit = false;
				if($echoit)
				{
					echo "Prefix: $prefix Suffix: $suffix<BR>";
				}
				if(($prefix == 0) && ($suffix==1))
				{
					break;
				}
				if(feof($f))
				{
					break;
				}
				while(!(($prefix == 0) && ($suffix == 0)))
				{
					if($prefix == 0)
					{
						$pocet = $suffix;
						$CurrentBit = 0;
						for($h=0; $h<$pocet; $h++)
						{
							$Data.=chr(freadbits($f,4));
						}
						if($CurrentBit != 0)
						{
							freadbits($f,4);
						}
						$pocetb += ceil(($pocet/2));
						if($pocetb%2 == 1)
						{
							freadbyte($f);
							$pocetb++;
						}
					}
					if($prefix > 0)
					{
						$pocet = $prefix;
						$i = 0;
						for($r=0; $r<$pocet; $r++)
						{
							if($i%2 == 0)
							{
								$Data .= chr($suffix%16);
							}
							else
							{
								$Data .= chr(floor($suffix/16));
							}
							$i++;
						}
					}
					$prefix = freadbyte($f);
					$suffix = freadbyte($f);
					$pocetb += 2;
					if($echoit)
					{
						echo "Prefix: $prefix Suffix: $suffix<BR>";
					}
				}
				for($x=0; $x<strlen($Data); $x++)
				{
					imagesetpixel($img, $x, $y, $Palette[ord($Data[$x])]);
				}
				$Data="";
			}
		}
		if($biBitCount == 24)
		{
			$img = imagecreatetruecolor($Width, $Height);
			$Zbytek = $Width%4;
			for($y=$Height-1; $y>=0; $y--)
			{
				for($x=0; $x<$Width; $x++)
				{
					$B = freadbyte($f);
					$G = freadbyte($f);
					$R = freadbyte($f);
					$color = imagecolorexact($img, $R, $G, $B);
					if($color==-1)
					{
						$color=imagecolorallocate($img, $R, $G, $B);
					}
					imagesetpixel($img, $x, $y, $color);
				}
				for($z=0; $z<$Zbytek; $z++)
				{
					freadbyte($f);
				}
			}
		}
		return $img;
	}
	fclose($f);
}

function freadbyte($f)
{
	return ord(fread($f, 1));
}

function freadword($f)
{
	$b1 = freadbyte($f);
	$b2 = freadbyte($f);
	return $b2*256 + $b1;
}

function freaddword($f)
{
	$b1 = freadword($f);
	$b2 = freadword($f);
	return $b2*65536 + $b1;
}