Subject:
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Re: Bricksmith 2.4: Faster. Much Faster.
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Newsgroups:
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lugnet.cad.dev
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Date:
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Wed, 16 Jun 2010 19:09:03 GMT
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Viewed:
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37318 times
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In lugnet.cad.dev.mac, Don Heyse wrote:
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In lugnet.cad.dev.mac, Don Heyse wrote:
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In lugnet.cad.dev.mac, Don Heyse wrote:
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In lugnet.cad.dev.mac, Remi Gagne wrote:
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In lugnet.cad.dev.mac, Allen Smith wrote:
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By the way, Bricksmith does not render conditional lines. I consider
shading to be a sufficient substitute, and conditional lines sound
difficult to optimize.
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Heh, you hit that problem too? I’ve played around writing an OpenGL LDraw
renderer based exclusively on display lists, but I can’t for the life of
me figure out how to handle conditional lines in this setup. Has anyone
else solved this peculiarly specific problem?
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You can ignore the conditional lines and achieve the same effect with
display lists using the stencil buffer techniques presented here:
http://www.opengl.org/resources/code/samples/sig99/advanced99/notes/node108.html
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And here’s a silhouette technique using BFC:
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.71.8503&rep=rep1&type=pdf
This technique and the conditional lines both target the same edges lines
where the front facing polygons meet the back facing polygons, so the
results should be quite similar.
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And another thing...
The BFC technique actually has an advantage over conditional lines
because it works on the entire scene after it’s been assembled. Whereas
the conditional lines at the edges of the primitives are created in
advance, and must predict what they’re going to butt up against when the
entire scene has been assembled. This prediction may not always be
right, resulting in missing conditional lines and some visible where
they should not be.
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So finally this brings us to a technique that combines the predictive
abilities of the conditional lines with the runtime advantages of the
stencil and BFC algorithms.
Think of the conditional line as a pair of triangles with a shared edge
line. You can ensure the two triangles are wound the same way by going
through the shared edge line in the opposite direction in the two
triangles. This means if we try to draw both triangles in a scene where
the conditional line should show then one of the triangles can be culled
by BFC. So we take advantage of this by drawing the conditional line
triangles (edges only) into the stencil buffer. Then we redraw only
the conditional lines and use the stencil buffer to pass only the
conditional lines that were drawn once. Conditional lines that were
drawn 0 times, or more than 1 time do not pass.
I think it could work. What do you think?
Enjoy,
Don
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Message has 1 Reply:
 | | Re: Bricksmith 2.4: Faster. Much Faster.
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| (...) Interesting, but complicated IMO :-) Shaders offer a much easier implementation, and (I suspect) a faster one. Geometry-shaders for preference, but the algorithm can be implemented using vertex-shaders or even ARB vertex-programs to support (...) (14 years ago, 16-Jun-10, to lugnet.cad.dev, FTX)
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Message is in Reply To:
| | Re: Bricksmith 2.4: Faster. Much Faster.
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| (...) And another thing... The BFC technique actually has an advantage over conditional lines because it works on the entire scene after it's been assembled. Whereas the conditional lines at the edges of the primitives are created in advance, and (...) (14 years ago, 16-Jun-10, to lugnet.cad.dev.mac, lugnet.cad.dev, FTX)
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