From Paul Pantera at Sun:
> GeometryInfo does a lot in the background. If you put your geometry
> into it as POLYGON_ARRAY and then immediately call getGeometryArray(),
> it will create a default triangulator and triangulate your data, then
> unindexify it, and then create the GeometryArray and pass it back.
> There's no other choice because you can't put polygons into a
> GeometryArray. The word "polygon" is never used anywhere in Java 3D
> except in GeometryInfo and the triangulator.
>
> To further expand this, the NormalGenerator and Stripifier only work on
> indexed triangles. Therefore, no matter what format your data is in,
> it will be converted to indexed triangles if you call the
> NormalGenerator or Stripfier. This is hidden from the user. If you
> send in quads and call the stripfier, you will get triangle strips out,
> and you won't know that your quads were converted to indexed triangles
> in the interim.
>
> If you send quads (or fans or strips) to the NormalGenerator, they get
> converted to indexed triangles before Normals are calculated. If you
> then call getGeometryArray(), the triangles are converted back to the
> original primitive in the most intelligent way possible. If it was
> originally fans or strips, it will attempt to stitch them back
> together, but it may have to break a strip in two if there was a hard
> edge in the middle of the strip. It does the same thing for quads.
> (There can't be a hard edge in the middle of a quad because the same
> facet normal is used by both sub-triangles of the quad).
>
> This probably rarely happens because most people aren't going to
> generate normals and then call getGeometryArray(), they're going to
> call the stripifier first. In that case, the data is left as indexed
> triangles and sent immediately to the stripifier. It's never converted
> back to the original primitive type.
>
> Keeping all that in mind, POLYGON_ARRAY is treated just like any other
> primitive by GeometryInfo. Before it can be sent to the
> NormalGenerator or Stripifier, it must first be converted to
> triangles. It uses the triangulator utility to do this. Where it
> differs from the other primitives is when you don't call the
> Stripifyer. If you call getGeometryArray() on POLYGON_ARRAY data
> without calling the stripifier, you will always get back individual
> triangles.
>
> So the answer to your question is yes, you don't need to call the
> triangulator explicitly (unless you want to specify the earOrder)
> because it gets called automatically when POLYGON_ARRAY data is used.
> Does it hurt to call it explicitly? Not much. The triangulator
> is smart enough to do nothing if the input data is already
> triangles.
>
> Homework:
>
> 1) If I put Quad data into GeometryInfo and call the NormalGenerator
> followed by getGeometryArray(), what will be the primitive of the
> returned data?
>
> 2) If I put Triangle Fan data into GeometryInfo and call the
> Stripifier followed by getGeometryArray(), what will be the
> primitive of the returned data?
>
> 3) If I put Polygon data into GeometryInfo and call the
> NormalGenerator then the Stripifier then getGeometryArray(),
> what will be the primitive of the returned data?
>
> 4) If I put Quad data into GeometryInfo and call the
> Stripifier then the NormalGenerator then getGeometryArray(),
> what will be the primitive of the returned data?
>
>
> Answers:
>
> 1) Quad. The quads get taken apart to calculate the normals,
> then they get put back together.
>
> 2) Triangle Strip. The input primitive type doesn't matter
> because you called the Stripifier.
>
> 3) Triangle Strip. Same as #2.
>
> 4) Don't do this! When you call the Stripifier, GeometryInfo
> will convert your data into triangles, and then the
> Stripifier will turn it into strips. Then GeometryInfo
> has to turn it back into triangles before it can call
> the NormalGenerator! Then, after calculating the normals,
> it will attempt to stitch the strips back together. Don't
> do this! You are doing tons of extra work and
> your strips aren't as long as they would have been.
> Always call the NormalGenerator before calling the
> Stripifier.
>
> -Paul
>
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