[Gmsh] Reclassify 2D does not work

[Martin Vymazal]

Dear prof. Geuzaine,

 unfortunately I never tried to use fltk or vtk myself as a library and I 
don't know their internals. I can only provide some observations as a user of 
both.

 I'm wondering what happens in gmsh for example when a user is trying to 
rotate a large 3D mesh with both surface and volume elements. Since you don't 
'see' the underlying volume elements, you only need to redraw the surface. 
When I switch off all volumes explicitly in visibility window, gmsh is 
suddenly more responsive. I guess vtk can do this automatically, but I wonder 
what's the level of sophistication of such algorithm which decides what (not) 
to draw as the view angle changes.
 
 Gmsh is also very slow when you decide to delete a few elements from the mesh 
through the gui. You select an element, confirm your choice and have to wait 
for some seconds before you actually see it disappear from the screen.

 I wonder if some of these issues are directly related to fltk, because for 
the Reclassify2D problem, just waiting for the reclassify dialog to pop up is 
very long. When you want to move the dialog on the screen (without actually 
manipulating the mesh), you again have to wait (easily 5-10 seconds depending 
on how big is the mesh).

The gui of gmsh built from source usually behaves better than a pre-built 
binary. Gmsh is more responsive in my linux laptop with nvidia card and closed 
source drivers than in my office computer, which has cheap on-board intel GPU, 
but faster cpu and twice as much ram (8Gb).

Please don't take this as criticism, I don't know myself what is the cause of 
these problems or how to solve them. This is as much as I can say about the 
speed issues paraview vs. gmsh from user point of view.

Best regards,

  Martin Vymazal


> > 
> > It's hard to process meshes with one opensource package, I usually use the
> > combination Gmsh-Paraview-Meshlab. I like gmsh, but its gui becomes
> > extremely slow with large meshes (say ~ 10^6 elements). ParaView is much
> > more responsive.
> Hi Martin - do you know how Paraview achieves this? Does it display the same
> amount of information?
> > Best regards,