Subject:
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Re: Parts as volumes (instead of surfaces)
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Newsgroups:
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lugnet.cad.dev.org.ldraw
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Date:
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Tue, 9 Apr 2002 21:28:07 GMT
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Viewed:
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252 times
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In lugnet.cad.dev.org.ldraw, Paul Gyugyi writes:
> If you're interested, take a look at my old Rayshade
> libraries that made the bricks from scratch using CSG.
> I'm especially fond of the L3G0 40-tooth technic gear.
>
> I've thought it would be nice to have "bounding boxes" for
> the bricks, for collision detection. Some tools for rendering
> dat files compute a bounding box on-the-fly as the brick is
> loaded, but this is not accurate enough to do collision detection,
> although could help to limit the number of bricks that need
> searched for potential collisions. I once did a rendering of
> a snow scene consisting of a pile of 1x1 and 1x2 white plates
> leaning on each other. I used bounding boxes and a physics
> modelling program to determine the shape.
>
> The BFC stuff can be useful for other things. The nVidia developer
> CD has a rendering program that highlights a spaceship by creating
> a halo effect. The halo is formed by taking each triangle in the
> model, making it a fuzzy transparent yellow color, and displacing
> it by a fixed amount in the direction of the normal (which we can
> find out easily if the part is BFC-certified).
>
>
> -gyug
>
> In lugnet.cad.dev.org.ldraw, Damien Guichard writes:
> > It has been said that, with ldraw parts, we have the geometry of TLG bricks.
> > This is rather optimistic. Because geometry would be CSG descriptions that
> > allow much more (although slower) than quads and triangles. CSG descriptions
> > allow part collision detection.
> >
> > Thinking about BFC statements I realised they also allow collision detection.
> > The prerequisite is having convex parts. Each polygon defines a tangent
> > plane, an "exterior" half-space and an "interior" half-space. A part is
> > defined by the intersection of these interior halve-spaces that are
> > organized in a BSP tree. I guess collision detection is then a standard
> > procedure on BSP trees. Or may be I am wrong and this is actually a much
> > more complex problem.
> >
> > Anyway, the remaining problem is that most (if not all, including Brick 2 x
> > 4) ldraw parts are not convex but concave. Is there any simply mean to
> > extend BFC with metacommands that split ldraw parts in convex subpart? Does
> > the topic deserve the effort? Any interest at all? Just an idea to see what
> > reply.
> >
> > Damien
I like the idea of CSG. Unfortunately I can not invest time in Rayshade and
alternate ray-tracers. I know they can have attractive features but I am
more a POV user. I must impose some limit to my (already too high)
diversification.
Of course, whatever how the volume is defined, "bounding boxes" or "bounding
spheres" is the best way to easily reject many costly collision checks.
Bounding boxes may be better than bounding spheres. However bounding volumes
is a secondary question, the primary question remains the actual volume. Is
it possible to just use current polygons? Switch to polyhedrons? Or switch
to CSG ? What is your opinion ?
I am also happy one can imagine creative effects using BFC. Would be too bad
if BFC is limited to display speed enhancement.
The SubSpace-Police-Outpost is one of the best MOC on the net,
Regards,
Damien
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Message is in Reply To:
 | | Re: Parts as volumes (instead of surfaces)
|
| If you're interested, take a look at my old Rayshade libraries that made the bricks from scratch using CSG. I'm especially fond of the L3G0 40-tooth technic gear. I've thought it would be nice to have "bounding boxes" for the bricks, for collision (...) (22 years ago, 9-Apr-02, to lugnet.cad.dev.org.ldraw)
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