Re: Anyone use edges in TriMeshes?

[Roger H. <rog...@mi...>]

On 2 Feb, 2007, at 16:54, James W. Walker wrote:

>> If the old renderer is continuing to be supported then fine, but if
>> the
>> new renderer is going to become a replacement then I would like
>> TriMesh edges supported at least when the Fill Style is
>> kQ3FillStyleEdges.
>>
>> Much less important, but it would be nice if vertices could still be
>> supported when Fill Style is kQ3FillStylePoints.
>
> I'm not sure we're on the same wavelength.  Of course
> kQ3FillStyleEdges and kQ3FillStylePoints will be supported.  I'm
> talking about the edges that can be specified explicitly in
> TQ3TriMeshData.

This is my wavelength:

In the caching code everything gets reduced to either markers,
points, lines, trinagles or trimeshes. Most things become trimeshes.
Trimeshes have explicit edges. There are no implicit edges.
We use kQ3FillStyleEdges to give the users a wire frame view,
and we also use an embeded kQ3FillStyleEdges to show
a wire frame on top of a geometry when editing certain geometries
so the user can see the edges and vertices he can move. This
is done in a view where all the other geometries  are drawn
solid. If you do not implement edges in Trimeshes, none of
this will work with your new renderer and I will have to use the
old one, which is fine as long as it is still supported.

Trimeshes have three collections of objects: vertices, edges
and triangles. The triangles themselves do themselves
generate lines, otherwise as most triangles abut other
triangles, for each edge it would get drawn twice, once
for each triangle either side of it. This would I think
double the size of the data passed to OpenGL when
doing a wire frame render, though of course this is
quite fast anyway, but when a cube is cached as a
trimesh, it SHOULD (though not currently) generate
edges for the twelve edges of the cube and should
generate twelve triangles, but it should not generate
edges along the split of each square face of the cube.
Currently it generates nothing and cube actually
disappear on wire frame, which is something we have
been apologising for for the last few years. We try
to get our users not use the cuboid data structure
for this reason and use a group of six polygons instead.

Similarly, in wire frame, do you really want to see the
tesselation of a polygon or just the edges?

Roger.