php & gd...outputting image problem

[devassocx]

Hi:

Have an application that is an endless loop structured something like this:

                    initialize
                        |
                        |
                    start loopa (infinite)
                        |
                        |
                    start loopb (infinite and conditional)
                        |
                        |
                       If event occurs terminate loopb
                          else redo loopb
                        |
                        |
                      imagepng($image);
                      imagedestroy($image);
                        |
                        |
                     redo loopa (forever)

The application executes properly. What does not happen however, is that the
graphics image is never displayed. If instead of making loopa an infinite loop
and execution is allowed to terminate and the ?> tag is executed then the graphics
image is displayed.

This same structure, if instead of attempting to output a graphics image, outputs
an echo (or similar) statement then it works as expected.

I have tried many different things to try to coax the graphics image to output
but so far have not found any resolution and I have also failed to find anything
on the web about this.

At this point, I am using apache2 webserver, php 4.3 in local mode with firefox and i.e.
browsers and windows op system.

Since the application depends on continous operation within the loop structures
rather than just a simple single pass I am soliciting assistance from those
more versed in this area.

Thanks in advance,

Bob Downs

[_theworks]

Could You post you actual code then some1 might actually be able to help...

[devassocx]

Here is about the minimim amount of code that should help
describe the problem....

<?php
// the initialization block of code is omitted...
// |
// |
// outer loop
for ($loopa = $rsetloop; $loopa <= $loopamax; $loopa++)
{
ob_start();
// inner loop
for ($loopb = $rsetloop; $loopb <= $loopbmax; $loopb++)
{
// bunch of code here to determine the event trigger...
}
// bunch of code here to get some data from a file, get an array
// from another file, update the array with new data
// |
// |
// |
// this is the final code section...this is where the graph output should happen
header('Expires: Sat, 01 January 2000 05:00:00 GMT');
header('Last-Modified: ' . gmdate('D, d M Y H:i:s') . 'GMT');
header('Cache-Control: no-cache, must-revalidate');
header('Pragma: no-cache');
header("Content-type: image/png");
// Output graph and clear image from memory
imagepng($image);
imagedestroy($image);
$loopa = 0; // this resets the loop index to make it infinite
flush(); // this & next line added, but makes no difference
ob_flush();
} // end of the outer loop
?>

[Weedpacket]

So you're generating a bunch of images, and then trying to put them all on one page with http headers in between? That's not going to work: one image per http response. If you want a bunch of images in a page you'll have to either (1) make one big image with all of the smaller images in it, or (2) write a page with <img> elements, each one requesting a single image.

That's assuming you don't mind leaving IE users out in the cold: otherwise it could be done using data: URLs.

[Nugen]

Above poster is correct - 1 image per call, no multi-images - that isn't how GDlib or using PHP files to generate dynamic images works.

header('Expires: Sat, 01 January 2000 05:00:00 GMT');
header('Last-Modified: ' . gmdate('D, d M Y H:i:s') . 'GMT');
header('Cache-Control: no-cache, must-revalidate');
header('Pragma: no-cache');

these headers also need to be removed. as soon as you set them its going to mime to PHP/html/text etc. These headers are not in the image standard.

[Weedpacket]

No, those headers are fine; they're there to ensure that the browser doesn't try to cache the image (and so mistakenly display one that's out of date). Those headers aren't in the image standard, true, but they're not in the HTML standard either - they are in the http standard, though.

[devassocx]

Thanks for everybody's input.

I think that for whatever reason, the function imagepng($image) only outputs to the buffer and not to the browser. Browser output only occurs at the conclusion of page load. This is unlike the action of echo or print_r which do output to the browser.

So I was forced to restructure the code to use the html refresh tag. Not quite what I wanted to to but I guess it will work in this specific application.

So unless there is some new info regarding this I think this will be the final answer as they say on that tv show.

Thanks again to everyone for their suggestions. The value of this type of
resource on the web is immense.

Bob Downs