a few issues with qwtplot3d

[Gerard V. <ger...@gr...>]

Hi Micha,

In the process of making Python bindings for QwtPlot3D, I have found the
following (minor) problems:

- your simpleplot program has a problem (which may only show up on X):
  part of the axes frame and the whole title do not show up, until I
  resize the simpleplot widget manually.  I am pretty sure that it is
  some initialization problem, because if I comment the statement
  plot.resize(800, 600) from main(), everything looks OK.
  (strange that the surface does not get chopped off).

- it took me some time to see that for you a tab means 2 spaces (all my tools
  on Linux interpret a tab as 8 spaces and display only 80 characters per
  line, so your code is pretty hard to read -- viewcvs also is confused:
http://cvs.sourceforge.net/viewcvs.py/qwtplot3d/qwtplot3d/include/qwt3d_plot.h?rev=1.17&view=auto )
  Uwe and I have the policy *not* to use tabs in Qwt (sometimes it happens,
  though).

- SurfacePlot::createNormals() is declared in the headers, but not defined.

- I do not like your definition of DataRows which leads to a lot of
  allocations or double[3].  I would define DataRow as:
  typedef DataRow std::vector<Triple>;
  and abuse the fact that sizeof(Triple) == sizeof(double[3]).
  IMO, it is not only more efficient but would also lead to cleaner code
  in qwt3d_gridplot.cpp (if you like, I can send a patch).
  (I am aware that GL vertices can be triplets or quadruplets, but that
   is maybe something for the future).

Just a few other ideas, since my problem of 3D plots on a 2D screen is that I cannot read
off coordinates of a point on a surface:
- Would it be possible to implement some cursor which moves on the surface (ctrl-x or ctrl-y
  for positive x or y direction and alt-x or alt-y for negative x or y direction)?
- Another type of "cursor" would be a plane parallel to the z-direction which cuts the
  surface. The plane can have a direction parallel to any vector in the x-y plane and
  have an offset with respect to the origin of the axes.

Gerard

PS: OpenGL is new for me.  I am quite impressed with how snappy QwtPlot3D behaves
with respect to Vtk and its Python bindings.