Re: your mail

[Atool Varma <varmaa@kenyon.edu>]

On Wed, 22 Sep 1999, fakhreddin mohtasham wrote:

> Hi D3DRM programmers,
> 
> as we know many attractive new games are written with pre-rendered
> images as backgrounds,I really confused in some scenes in 3D,for
> example how a real 3D charactercan be hide behind a wall while the wall has 
> been rendered before andthere is no mesh for the wall in the scene.

	I think this could be done with z-buffer compositing, but it's
just a guess.  That is, the 3d rendering program (3D Studio MAX, etc)
could pre-render the image with the alpha channel layer being indicative
of the z-buffer (i.e. how far away the pixel is from the camera).  Then in
the actual game, the code could blit the image directly to the framebuffer
and the alpha channel information directly to the z-buffer, and then
render the rest of the polygons as normal.  That way if there was a wall
in the pre-rendered image and there was a polygon character behind it,
when the polygons of the character are rasterized, some of the pixels
would be occluded by the wall because the z-buffer values of those pixels
would show that the wall pixels are closer to the camera than the
polygon pixels.

	This would be easy to do with a software renderer, but I don't
know if it's possible to write directly to a hardware z-buffer, since I've
never done any hardware-accelerated 3D rendering before.

		Atul

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