Re: [Dri-devel] TCL/SW lighting differences

[Brian P. <br...@tu...>]

Felix K=FChling wrote:
> Hi,
>=20
> I made a small programme to illustrate the TCL/SW lighting differences.
> It displays a square consisting of 10x10 quads which is lit by one
> lightsource. The distance between the lightsource and the square is
> changed periodically. With TCL this has the desired effect, with
> software lighting it doesn't have any effect at all. This looks like an
> optimization that assumes lightsources to be at infinite distance. I
> attached the programme. With a macro you can switch between diffuse and
> specular lighting.
>=20
> So the lighting problem described with FlightGear could actually be a
> bug in FlightGear that just isn't visible with software lighting.
>=20

There's a bug in your program.  The GL light position is a homogeneous
coordinate (4 components) but you're only providing 3 components:

     GLfloat lightpos[3] =3D {0.0, 10.0, 0.0};

The 4th coordinate is effectively random.  Changing this to:

     GLfloat lightpos[4] =3D {0.0, 10.0, 0.0, 1.0};

Fixes the problem.

-Brian