[vtkusers] vtkTriangleStrip and empty vtkSTLWriter output

[Ben Boeckel]

On Wed, Oct 14, 2015 at 22:34:25 -0400, David Cole via vtkusers wrote:
> Shouldn't the STL writer detect that its input contains non-triangles, and
> **automatically** insert a triangle filter to produce correct output? Or,
> at the very least, spit out an error message saying "here, insert this code
> before calling Update/Write, and it will work like you want it to" ... ?

Well, it used to drop vertices past the third on the floor (silently),
but now it should be erroring out about non-triangles at least:

    commit 9a00db82900bd15442cc471143c4e5dd1ac09a2d
    Author: Ben Boeckel <ben.boeckel at kitware.com>
    Date:   Tue Feb 25 17:16:58 2014 -0500

        STLWriter: Raise an error for non-triangles

        The STL format only supports triangles and previously, it just
        truncated polygons silently. Cause an error to occur when this
        happens so that users know.

        Change-Id: I9c2f96d887074943130a8442d6796cb0c2ce1bbf

The commit is in VTK 6.2.0.

> (Similarly for rendering crappy polydata using the polydata mapper: it
> requires up-to-date normals to render with proper lighting and shading, and
> seems like the perfect candidate for **automatically** inserting a polydata
> normals filter. This might be harder to detect that the normals are not up
> to date, but sure would have saved my team some time recently...)

It should error out like the STL writer for bad input at the least.

> Would these types of improvements be welcome additions to VTK, or am I
> missing some case where you would NOT want this type of behavior?

As long as it lets you know that your data is bad and that (and how) it
is being fixed is warned about, I don't see any reason why such an
auto-fixer filter couldn't exist (whether it is named vtkSTLWriter or
something else is a different question I don't have enough feel too
strongly about).

--Ben