[SOLVED] Loop problem in GD

[AV1611]

Can anyone tell me why this image quits drawing after 255 lines?

 

<?php
header("Content-type: image/png");
$im = @imagecreate(255, 512)
    or die("Cannot Initialize new GD image stream");
$background_color = imagecolorallocate($im, 255, 255, 255);
$q=rand(1,3);
$a=0;
$b=0;
$c=0;
$i=0;

while($i <= 511){
if($q==1){$color=imagecolorallocate($im,$b,$c,$a);}	
if($q==2){$color=imagecolorallocate($im,$a,$b,$c);}	
if($q==3){$color=imagecolorallocate($im,$c,$a,$b);}	
imageline($im, 0, $i, 254, $i, $color);
if($i < 255)
	{$a++;}
$i++;
}
imagepng($im);
imagedestroy($im);
?> 

[BlueSkyIS]

because the image is only 255 pixels wide?

[AV1611]

Unless I'm just blind, $i is on the Y axis, and that is set to 512...

 

Or am I really confused :/

[BlueSkyIS]

of-the-top guess. here is the result i get:

 

http://www.blueskyis.com/test.php

 

is that right, or what are you seeing?

[AV1611]

That yields a 255x255 box.  It should be 255 wide x 512 high

Why is it not drawing after the 255th line?

[Yesideez]

Just had a play, see if this works:

 

<?php
  header("Content-type: image/png");
  $im=@imagecreate(255, 512) or die("Cannot Initialize new GD image stream");
  $background_color = imagecolorallocate($im, 255, 255, 255);
  $q=rand(1,3);
  $a=0;
  $b=0;
  $c=0;
  for ($i=0;$i<512;$i++) {
    if ($q==1) {$color=imagecolorallocate($im,$b,$c,$a);}	
    if ($q==2) {$color=imagecolorallocate($im,$a,$b,$c);}	
    if ($q==3) {$color=imagecolorallocate($im,$c,$a,$b);}	
    imageline($im, 0, $i, 254, $i, $color);
    if ($i < 255) {$a++;}
  }
  imagepng($im);
  imagedestroy($im);
?>

[GingerRobot]

Well, with a quick test of moving the call to imagecolorallocate() outside the loop, it appears that there might be a limit on the number of times you can allocate a colour.

 

I've looked at using imagecolordeallocate(), but i can't get it to work.

[AV1611]

Same problem.

 

Box is 255x255 not 255x512

 

Funny thing is, this is 255x512... is this a bug?

 

<?php
header("Content-type: image/png");
$im = @imagecreate(255,512)
    or die("Cannot Initialize new GD image stream");
$background_color = imagecolorallocate($im, 255, 255, 255);
$q=rand(1,3);
$a=50;
$b=50;
$c=50;
$i=0;
$color=imagecolorallocate($im,$b,$c,$a);	
while ($i<=512){
imageline($im, 0, $i, 254, $i, $color);
$i++;
}
imagepng($im);
imagedestroy($im);
?> 

[BlueSkyIS]

Well, with a quick test of moving the call to imagecolorallocate() outside the loop, it appears that there might be a limit on the number of times you can allocate a colour.

 

I've looked at using imagecolordeallocate(), but i can't get it to work.

 

that's what i'm seeing here, too. very odd. could be a bug.

[GingerRobot]

Indeed. A google search confirms thats the problem, and you can get round it by using imagecreatetruecolor() rather than imagecreate().

[Yesideez]

I copied the image and pasted into MSPaint and I can see that a 255x512 image is being made just that the bottom half is remaining empty. Just for debugging purposes, change the background color to something contrasting like 255,0,255.

[AV1611]

Well,

I got it to work. I change from imagecreate()

to imagecreatetruecolor()

and it works.  Even though I am only using 256 colors, I think it gets mad if you call a color more than 256 times... it treats each as a color on the pallet maybe?  Dunno, but either way, that's one to remember...

[Barand]

If I run your original posted code I get a completely filled image 255x512 with a gradient from black to blue (or red or green) for the whole of the image; black at top, blue (or red or green) at bottom.

[BlueSkyIS]

odd, what version of PHP and GD are you running?

[Barand]

PHP : 5.1.2

GD  : 2.0.28

 

[BlueSkyIS]

hm, i'm at PHP 5.2.0, GD 2.0.28 and it doesn't work for me. i am curious...

[Barand]

I get same (correct) result with PHP 4.3.9, GD 2.0.28

[Barand]

Resulting output attached

 

[attachment deleted by admin]

[BlueSkyIS]

i get correct ouput in 4, but not 5, same GD version. oh well, i can live with it, but it's good to know in case i see anything similar happen elsewhere.