Hi all,
I have been working on my uDG project, and I've been playing around a bit with jumping in 3d- though I've been playing video games a lot time, it's become a lot more obvious to me that it really helps to have a shadow to see where you are.

Now, I'm a graphics person myself, so I know a bunch of expensive ways to do shadows (shadow volumes, shadow buffers, shadow maps) though what I would like to do for uDG is a really simple, cheap way to do shadows that is mainly functional, but doesn't look too bad.

What comes most obviously to mind is just using a black circular texture, and just running a multiple pass on the geometry (or use multi-texturing.) The slowest way to do this would just render the entire visible part of the scenery (not going to bother with object->object shadows) again for each object I want to shadow. You could then speed this up by making some more geometry-ish trees so that you only draw the polys that the shadow will appear on and so forth, though again I am trying to do something simple so I get done in time.

You could do some tricks with the stencil buffer as well I think, though I would like to avoid using it, as I'm not sure how wide the hardware support for it is.

Anyone have any thoughts/ideas about doing cheap shadows that don't look too bad?

If the number of planes the shadow is going to be projected on is limited, you can setup a projection matrix ( in the mathematical sense ) and simply draw the object casting the shadow another time in black. IIRC, the Red Book even has the complete equation for that matrix in one of the later chapters.

Well, it is easiest to play when you have the shadow directly underneath you, as opposed to casting it at some angle. And when it is underneath you it doesn't need to be much more than a darkened circle. But that probably doesn't help you at all :-)

No time for more than a bit of code I wrote a while ago; probably has various dependencies on other files, and is Obj-C++, but should be reasonably helpful. IIRC it loads a heightmap from a TIFF and lets you add shadows and splatters which get drawn over the land. Probably not dreadfully efficient, and I'd certainly do some things differently if I was writing it now, but it might be helpful:

http://www.alexanderatwater.com/wibble/floors.zip