Re: [Algorithms] Scaling Models

[Davide P. <da...@pr...>]

> If you set a scaling matrix as part of the transformation pipeline what
> happens to the normals?
> I currently use D3D\OpenGL to do the transformation but use my own
lighting
> code. If I set a scaling factor to each of the 3 axes the angles of most
of
> the faces in the model will change (unless the scaling factor is the same
> for all three axes). An extreme example is when XSc=ZSc=1.0f; YSc=0.0f;
All
> normals will either become 0,0,0 (for triangles with a normal
perpendicular
> to the Yaxis) or 0,1,0 for all other normals.
>
> Rebuilding the normal list is not an option as the models are shared
> multiple times with different scalings.
>
> Anybody else encountered this problem? And how does D3D\OpenGL cater for
> this?

There is a very nice doc on opengl site called :

Avoiding 19 Common OpenGL Pitfalls

oglpitfall.pdf

Written by Mark J. Kilgard that cover this topic.


Davide Pirola
www.prograph.it
www.protonic.net