README.stefan

Modifications to CQ3A to support reflection mapping
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I implemented reflection mapping for Cave Quake III
Arena by Paul Rajlich.

Sphere environment mapping was very simple to implement,
but looked awful in stereo, particularly for all the
reflective health spheres sprinkled over the levels.
Sphere mapping looks sort of OK for more irregular
objects and monoscopic views, but not in CQ3A.

Instead, I implemented (with some effort) a variant of
dual paraboloid environment mapping. On platforms which
support cube environment maps or the Nvidia extension
GL_NV_texgen_reflection, this is fully hardware accelerated.
Hardware accelerated environment maps are activated by
default.

To support hardware platforms where an appropriate texgen
extension is not available (for example the SGI Onyx2),
I also implemented a software workaround. It uses some
CPU power to calculate the reflection vectors in software.
This it is not significantly slower unless too many
objects in the scene are reflection mapped, and if you
have an Onyx2, you can probably spare the CPU cycles.
This mode will work on all OpenGL 1.1 implementations,
without any special extensions.

The software workaround is visually very close to what
was used in the original game, so if you want the original
Q3A look to the maps, use this mode.
Compiling with -DSW_REFLECTION activates the software-assisted
reflection mapping. It looks a little better, but requires
some additional CPU power.

Strictly speaking, neither the hardware nor the software
reflection maps are dual paraboloid maps. Because of a
limitation in the current CQ3A multi-texturing code, the
hardware version performs only one pass where two are needed,
so it is actually "single paraboloid mapping". Also, since the
original game uses a software method for reflection mapping,
there is no alpha map on the Q3A environment textures, so
that would have to be patched in afterwards to make true
dual paraboloid maps possible.
To get a better look to the single pass paraboloid mapping,
I chose to orient the environment map differently from in
the original game: the pinch for the "back-facing" reflection
directions points downwards in order to hide it better from
common view angles. The software reflections are oriented
like in the original game, though.

BUGS:
Texture coordinate animation on environment mapped shaders,
like the ones on golden and mega health spheres, look wrong.
I tried to fix that, but I have no solution yet.


Stefan Gustavson, ITN-LiTH (stegu@itn.liu.se) 2001-08-28