[Gmsh] Bug Report Involving Surface Normals

[Christophe Geuzaine]

> Layne Wright wrote:
> 
> Greetings All!
> 
> When exploring the geometry options in Gmsh, I stumbled upon a problem
> with display
> surface normals. I was using tutorial file 't2.geo' at the time.
> 
> With 'Points/Curve/Surfaces' enabled, I entered a non-zero value in
> the normals field. Upon clicking OK,
> the message window comes up with the message 'Fatal Error: Wrong list
> index (read)' repeating until
> one clicks the CANCEL button. At this point, Gmsh is no longer
> responding to buttons, and the task
> manager must be used to shut the program down. NT recovers gracefully
> from this crash, but Windows 98
> subsequently given 'Out of Memory' errors when trying to run other
> programs, and can't be shut down using
> the 'Start' bar; one must use 'RESET' to exit Windows (a pretty hard
> crash).
> 
> I did notice some window transparency issues in the NT crash, but I
> did follow the installation instructions
> regarding 'opengl32.dll' in the readme file. Included at the end
> of this email is a excerpt from the gmsh error log.
> 
> Subsequent explorations of this bug reveals that a normal display can
> be had if one turns on the corresponding
> number displays for points, curves, and surfaces. The normals do
> change length with the value entered in the
> NORMAL field, but the directions assigned the normals does'nt appear
> to follow any rule corresponding to the
> sense given when defining plane surfaces. Gmsh will crash again,
> however, if one then reloads the '.geo' file.
> 

Thanks for the feedback! I corrected the bug in my version, so it will
be fixed in the next public release. This option is not very useful,
though: as you found out, the direction reflects the internal
representation of the surface by Gmsh, which can be different from the
definition you made in the .geo file. So this option is mostly useful
for debugging purposes (for us :-).

Christophe

-- 
Christophe Geuzaine

Tel: (626) 395-4552    http://www.geuz.org
Fax: (626) 578-0124    mailto:geuzaine at acm.caltech.edu