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 04:09:25 GMT
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Viewed:
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320 times
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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
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Message has 1 Reply:
 | | Re: Parts as volumes (instead of surfaces)
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| (...) 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, (...) (22 years ago, 9-Apr-02, to lugnet.cad.dev.org.ldraw)
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Message is in Reply To:
| | Parts as volumes (instead of surfaces)
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| 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 (...) (22 years ago, 6-Apr-02, to lugnet.cad.dev.org.ldraw)
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