imagerotate() oddities.

[Balthazar]

Hey all, bout time I finally registered around here, been lurking long enough.

Anyhow, I have come up against a very....unusual, issue with PHP+GD.

I'm running 4.3.1 with the included GD php-gd rpm on Mandrake 9.0.

I have written an image gallery script and one function I wished to add was the ability to rotate images.

This is one of many itterations of code I used to rotate the image:

$src_img = ImageCreateFromJPEG($filename);
$rotated = ImageRotate($src_img,$degrees,0);
ImageJPEG($rotated, $filename, 85);

As long as $degrees is negative, it works fine, BUT, it only works once, try to rotate the image again to the right (or left) and it cuts the image off.

Now when I try rotating to the LEFT, that code wont work, I had to use this:

$src_img = ImageCreateFromJPEG($filename);
$preRotate = ImageRotate($src_img,"-90",0);
$rotated = ImageRotate($preRotate,"-180",0);
ImageJPEG($rotated, $filename, 85);

Now thats a simple enough workaround, but I STILL cannot rotate more than once on a given image.
And I dont understand WHY a negative value would work, but positive wont?
And I am 100% at a loss as to why I cannot rotate an image more than once. Nearest I can guess imagerotate() does something to the image that messes it up when rotating again, but how could that be? If it sees JPEG and it sees the right width/height it should work.

Anyway, if anyone can shed some light on these issues I would be VERY appreciative, nothing worse that having to tell users "um, yeah, don't rotate the image more than once....and I dont know why".

Thanks a bunch for any help guys!
Now I'm off to see if I cant actually contribute for a change 🙂

[tekky]

imagerotate() functions on the canvas level.... (if you are familiar with photoshop) not the image level....

it will rotate the data on the canvas... but not modify the image H/W so its not in essence rotating the IMAGE itself, only the data in the IMAGE...

so if you have a hxw of 20x5 and rotate it 90 degrees... you would hope to have a 5x20 image on its side... instead you have a 20x5 image still with a 20 pixel wide strip of data showing around the middle of the image surrounded by a black or some other color background on either side....

in order for imagerotate() to fully display an image, you need to take into the account the new dimensions of the rotated image... (I'm fairly certain either here or on php.net there is a snippet of code that illustrates and "fixes" it -- infact I think I pasted that snippet on here somewhere about a month ago... if you want to try searching image and my username)

[Balthazar]

Yeah, I was reading the documentation sans user comments. But even the snippet of code I found there didn't work. So I just wrote my own. For anyone who cares (or wants to critique) here it is:

$filename = $GET[target];
$degrees = $GET[angle];
$imagesize = getimagesize($filename);

$x = $imagesize[0];
$y = $imagesize[1];

if($x >= $y)
{
if($degrees == "-90")
{
$src_img = ImageCreateFromJPEG($filename);
$rotated = ImageRotate($src_img,"-90",0);
ImageJPEG($rotated, $filename, 85);
}
else
{
$src_img = ImageCreateFromJPEG($filename);
$preRotate = ImageRotate($src_img,"-90",0);
$rotated = ImageRotate($preRotate,"-180",0);
ImageJPEG($rotated, $filename, 85);
}
}
else
{
if($degrees == "-90")
{
$src_img = ImageCreateFromJPEG($filename);
$a = $y / 2;
$b = $x / 2;
$pos = $a - $b;

$placeholder = imagecreatetruecolor($y, $y);
imagecopy($placeholder, $src_img, $pos, "0", "0", "0", $x, $y);
$rotated = imagerotate($placeholder, "-90", 0);
$newImage = imagecreatetruecolor($y, $x);
imagecopy($newImage, $rotated, 0, 0, 0, $pos, $y, $x);
imagejpeg($newImage, $filename, "90");
}
else
{
$src_img = ImageCreateFromJPEG($filename);
$a = $y / 2;
$b = $x / 2;
$pos = $a - $b;

$placeholder = imagecreatetruecolor($y, $y);
imagecopy($placeholder, $src_img, $pos, "0", "0", "0", $x, $y);
$rotated = imagerotate($placeholder, "90", 0);
$newImage = imagecreatetruecolor($y, $x);
imagecopy($newImage, $rotated, 0, 0, 0, $pos, $y, $x);
imagejpeg($newImage, $filename, "90");
}
}

[tekky]

resource imagerotate ( resource src_im, float angle, int bgd_color)

note you are supplying ANGLE as a string which could end up being interpretted by PHP as something other than -90....

try using just -90 not "-90"