[Gnu3dkit-discuss] Sharing geometry

[Brent Gulanowski]

Is it better to have multiple shapes sharing one geometry or multiple 
groups sharing one shape? It appears the G3DGeometryBackend is designed on 
a 1:1 between shape and geometry. Can multiple groups reference the same 
shape easily enough?

What if there was a kind of thing, say a spaceship of a certain type, and 
instead of the parts being separate shape it had been optimized down into 
one shape with one geometry mesh (I think its called). Now you want to 
have fifty of these spaceships. So we have a single geometry object and a 
single shape to manage it. It is counter-intuitive to then make a group 
object with a single spaceship shape in it, but it seems like it would 
work fine. It's just a bit inefficient because then the individual 
spaceship representations have to talk to the shared shape through the 
intermediary of an array holding only one object.

I do see problems with shared geometry in a detailed simulation, but I 
think that the memory savings would be worth the effort to solve them.

For example, frame-based animations: Different world entities may be of 
the same type and use the same geometry, but they would not all be in 
synch for their animations. Quake 2 character models are a typical example.
 Except in Quake games, you might have five or six character entities 
using the same model, so you may as well not bother sharing. In a 
simulation of hundreds of entities or more (flocks of birds, fish, an army,
 cars on a freeway) duplicating the geometry would be unsustainable. A 
couple hundred sparrows wouldn't flap in unison, but the same flapping 
motions out of synch would be acceptable.

In my game I might have a couple dozen enemy robots with very simple 
frame-based animations: spinning antennae, waving pincers, whatever, just 
for looks. It would be nice to have animated textures, too, in the future.
 So there would be a small set of fixed meshes, and each robot would worry 
about when to start a particular animation sequence. Some frequently 
occurring entities won't have any animations at all. So should I make a 
new GraphNode for non-animated shared-shape entities, and a new Group 
object for animated shared-shapes entities?

For speed I'll probably want the various geometry objects that are part of 
an animated sequence to return the same min/max values and avoid 
triggering a recalculation of the bounding box every frame for every 
object -- that would be very expensive.

Thanks,

Brent
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