PHP仿GD打开BMP图片

/**
 * 类似GD库打开图片, 打开bmp格式图片
 * $file : 图片路径
*/
function imagecreatefrombmp($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;
}