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Access to OpenGL Depth buffer

Started by Seyedof Jul 23, 2001 at 3:48 PM 5 replies 1.7k views

Original Post

Jul 23, 2001 at 3:48 PM

Is this scenario possible? I have written a terrain engine which renders to a standard windows DIB surface, it has its own depth buffer (eg an array of floats). No i want to add some guys and monsters to my engine and render them via opengl , is it possible to tell the opengl to do its rendering on my DIB? i wanna first draw the land by my own rendering engine and then draw the other stuff like objects onto it, is it also possible to tell opengl to use my depth buffer and draw the stuff againt it ?? Thanks

Krippy2k

Jul 24, 2001 at 12:59 PM

Hmmmm. Check this out:

http://trant.sgi.com/opengl/examples/win32_tutorial/simpledib.c

Seeya
Krippy

Krippy2k

Jul 25, 2001 at 10:53 AM

Yeah, well he wanted a way to render to his DIB and that will do it just fine and will do it pretty fast

Copying his DIB back to the front buffer is another issue. That code was only meant to represent a way to render to the DIB and did not bog down on device copying algorithms. There are much faster means available than BitBlt.

Loading your own depth buffer is not real difficult and is pretty well documented.

But I agree that generally anything with the words Device and Independent in the definition of the acronym are destined to snaildome in the scope of a real 3D game. But perhaps he just wants to see if he can do it and not necessarily be concerned about the speed issues.

Better him than me. lol

Seeya
Krippy

Seyedof

Jul 27, 2001 at 11:59 PM

Thanks to all you guys, im used to write my engines in DIB, coz it is easier to start an engine and also easier to debug.
Ill convert them to DX or OpenGL after the development phase, and god damn it im a software rendering kid

Sometimes it is necessary to do everything via GDI specially in Non-Game applications...

OpenGL neither DX and none of the accelerators out there are capable to do voxels and you should do it via software, polygons really suck ( Delta Force3 is poly != Delta Force2 is voxel ).

BitBlt is not that slow, but StretchDIBits is real slow thing but if you choose a dib pixel format which is the same as your video mode depth blitting becomes much faster coz no color depth conversion is needed to blit your dib to the screen (done by GDI)

Well i got the answer to the first question, but for the second one :

I''ll clear the GLs depth buffer, draw my landscape on the DIB as well as updating the GLs depth buffer by z values from my landscape renderer, then i draw both objects and their depth buffer with GL, this way it will render objects against the depth of landscape.
ReadPixels seems to be slow, is there any way to get a pointer to depth buffer?

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