How to dynmically draw picture in php gd - php

Question

Hi I have searched the web for 2 days but did not accomplish what I am looking for.
I have an apache server which will be accessed by 146 students. the user picks an angle from dropdown lets say 45 degress, then user clicks CALCULATE button. Then user clicks DIAGRAM button to see how the sine graph looks like.
Works like charm when i write the image to a file e.g: imagepng($img,"diagram.png");
Now the problem is that the diagram.png will always get overwritten by the last user. So for example if another user logs in and calculates the Sin 135. Both users will see Sine 135 because filename is hardcoded since there is conflict of filename.
I have searched the web on how to create the image dynamically instead of writing to a file and then reading the file. I have come across the following but not working:
base64_encode and decode
What would I have to do to my code of imagepng(...., ...) mentioned above to make use of base64 so I can actually draw the picture of already processed data. Let assume if I comment out the imagepng(..) code, then what do I replace it with. I hope I don't have to change my code a whole lot.
Please help
thanks
Amit

Answer 1

The filename argument to imagepng is optional. From the manual:
filename
The path to save the file to. If not set or NULL, the raw image stream will be outputted directly.
You would just need to send a png header at the top of the script and you would get the image as output for that script.

Answer 2

It's hard to tell without seeing you code how it is structured
but if once the user submits the form all you do is show the image by itself, then you can do something like this.
// make sure nothing else is out put before this otherwise it will stuff up the header
header('Content-Type: image/png);
imagepng($img);
If you embed the image into an html page as the result, then your best best would be to change the url of the image on the success page to something like this.
<img src="/path/to/file.php?deg=45" />
Then in the file.php
$deg = $_GET['deg'] + 0; // make sure it is a number
$img= function_render_graph($deg);
// make sure nothing else is out put before this otherwise it will stuff up the header
header('Content-Type: image/png);
imagepng($img);
By using a GET request, rather then a POST request then the image will likely be cached by the browser, so it doesn't need to be rendered each time. (Given that you have a drop list of angles, there must be a limited number of graphs that can actually be drawn)

Answer 3

Draw_Resultant_Prism_Graph (parameters)
{
$img = imagecreatetruecolor(800,750);
....
....
...
the following lines captures the data from output buffer and displays on same screen
***some version of IE have some issues mostly the dumb terminals where IE update is ADMIN
***restricted
ob_start();
header("Content-type: image/jpeg");
imagepng($img);
$output = ob_get_contents();
ob_end_clean();
imagedestroy($img);
echo img src="data:image/jpeg;base64,'.base64_encode($output).'"
user tags around img above and semicolon af
}