Hi,

On Tuesday 17 November 2009, Paul Martz wrote:
> OK, final flip-flop: I really did encounter a NULL viewport problem. It
> occurs on a single GPU dual-head Win32 configuration. The viewport comes
> back NULL in this case, and the app crashes. Oddly, if I just pass in
> zero for the width and height, the app works for the most part. Seems to
> have some flicker in this case though. I've attached my code, which
> might still require some modification in the NULL viewport case.
>
> The attached code also contains the compile fix for Windows math routines.
Ok, I will see how I can initially get the right screen size.

So, since you appear to get the correct picture even if the initial size is 
(0,0), I assume that you get an osg resize event in the event visitor when 
the window is created?

I do not get that on X11, if this is sent on Win32, we probably should also 
send that on X11.

This would actually solve this issue, since I do only need the initial size. 
On a resize, the  event visitor resizes the textures ...

> And I also changed the clear color to white, so you might want to change
> that back. I noticed the clear color is hard-coded, so I assume this is
> unfinished code that you're going to modify anyway?
Well, there is some room here. But the Clear color for the pre render cameras 
should have 0 alpha. The color does not matter. For the compositing step, the 
clear color is set to the osg default.

> Thanks for posting this and letting me look at it, very informative.
Well, this is by far not the only possible implementation.
If you have a better one, I am interrested too.

Things to consider is to do that in a CullCallback without the need of a 
static amount of cameras.
Also, I would wish that osg's cameras/rendering backend would provide some 
hooks for such image based stuff so that we can have a camera that 
automatically renders into a screen sized texture and a compositing step that 
automatically sets up texture coordinate lookup for the screen sized stuff 
(texture rectangle, nearest interpolation, etc ...).
Once I have a better picture of what is needed here and could be reused ...

Greetings

Mathias

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