Fixed bug in second order mesh of closed curves

New options to enable/desable all default post-processing/solver plugins

add error check in Oriente()

add point with 'e', too

proof of concept for unproject (e.g. to add points with the mouse)

fix gcc warning + add "cancel" button to make the dialog look like
the other ones

- make the rotation matrix a matrix of doubles (instead of floats)

- store the modelview and the projection matrices in CTX

- new unproject() routine to transform window coordinates to model
  coordinates

- cleaned up all the static variables in the Opengl_Window class

- small fix to reduce normal clamping when zooming

Say we didn't find any solver plugins if GMSHPLUGINSHOME is not defined.

This is not perfect, but it allows us to *not* display the annoying
popups for "regular" users, while still registering JF's solver plugin...

'External data source' -> 'Data source'

if we have no geometry and no mesh, use the max of all view bounding boxes
(instead of the bounding box of the last view only)

typo

small cleanup + better error detection

allow x,y,z in expressions

init mesh fails for very thin regions

forgot to update help strings

The new "External data source" option makes the "Vector type->Raised
view" unnecessary. Just select "Vector type->Displacement" and choose
the data source from any other view in the list--including "Self"!

added small option to color the arrows representing a vector field
according to the data from another view

new option to draw the arrows with a fixed size

added a call to GUI::check() to make the GUI more responsive

add note on tensor field display

2nd order view example from JF

new solver options: SocketCommand and NameCommand (patch by
<C.Stott@surrey.ac.uk>)

fixed small syntax mistakes (missing semi-colons, etc.)

- added a couple of entries in the FAQ
- inluded the FAQ in the texinfo manual
- merged README.gui in the texinfo manual

shorter Draw_TensorElement routine

make displacement drawing code much shorter

Generalized "Raised scalar view" vector type: one can now also raise
vector and tensor views. (It's now simply called "Raised view".)

small fixes for last commit:

- only delete view.adaptive if we really delete the view (we might want to
  use the adaptive data in a duplicate view)

- add missing opt_view_global_zoom in update_view()

- don't even try to open StructuralSolver's data files if GMSHPLUGINSHOME
  is not defined

New high order interpolation.

JFR

minor fix: don't change xyzv::eps permanently in smooth()

fix minimum height of the solver window (was a bit too small)