Subject:
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Re: Why Type 5 Lines?
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Newsgroups:
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lugnet.cad.dev
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Date:
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Wed, 17 Apr 2002 19:40:36 GMT
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Viewed:
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386 times
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In lugnet.cad.dev, Kyle McDonald writes:
> Fredrik Glöckner wrote:
> > On the contrary, I think that type-5 lines are very useful, and an
> > interesting solution. They are a nice way to make sure that rounded
> > objects are outlined with a contrasting colour, no matter where the
> > viewpoint is. The rendering of cylinders and spheres is greatly
> > enhanced byt type-5 lines, I think. You can try yourself to view
> > objects with or without type-5 lines in L3Lab. Use the menu under
> > "View".
>
> I believe that there are other ways to put these lines in, as long
> as you are *only* planning on using them to show the 'visible' edge
> of a curved surface. This is actually a question I've been meaning
> to ask around here, Have type5 lines been used in 'other' ways in
> the Ldraw library? I don't know what other special effects you could
> achieve, but it wouldn't surprise me if there were some? Does anyone
> know?
>
> > By the way, is the "type-5" solution a common one in the CAD world, or
> > was it sort of invented by Jessiman? I don't know enough about CAD to
> > answer this myself.
>
> I don't know if something similiar might ahve been used early on,
> but I don't remember seeing anything like it lately. This may be because
> OpenGL and other libraries have other ways of achieving the same effect.
>
> In order to get OpenGL to do this for you though you need to have the
> polygons that represent the curved surface tied together in a 'strip'.
> If you can do that, then you can have OpenGL render them once a solid
> faces, and again as a wireframe. In my experience, when OpenGL renders
> strips and fans as wireframes, it will only draw the edges required to
> show where the curved surface disappears from view.
Tell more about this. I just tweaked a version of ldview to display
type 5 lines, but only for surfaces that haven't been replaced by
quad strips. It looks good with primitive substitution turned off, but
with this automagic wireframing of strips it could have the best of
both worlds.
> This is the main reason why I'm trying to automate 'stripifying' the
> LDraw polygons. The Rendering Library I use has no way for me to tell
> it wether to draw a line or not at final render time. It would be pretty
> hard for me to even go through ahead of time an figure out each type5
> line based on the view point, but that maybe possible. Instead though,
> I'm putting my trust in this 'feature' of how strips and fans are drawn
> so that I can get the same (or close) drawings, and just ignore the
> type5 lines during loading.
That would be fantastic, but I have my doubts. I suspect you'll end
up with lines that you don't want where various strips join. Now if
you can somehow turn everything between the type 2 lines into a single
strip you might have something.
> Of course if they've been used for other things as I asked above then
> I may have to make other arangements - Or just live with the differences
> in the output. :(
I'm pretty sure outlining curved surfaces is their only use.
Don
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Message has 1 Reply:
 | | Re: Why Type 5 Lines?
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| (...) I'm curious to. Everything I know about how OpenGL works says that drawing the strip as a wireframe after drawing it solidly would either produce Z Buffer noise, no wireframe at all, or wireframe all over. However, it may be that there is some (...) (22 years ago, 17-Apr-02, to lugnet.cad.dev)
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Message is in Reply To:
| | Re: Why Type 5 Lines?
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| (...) I believe that there are other ways to put these lines in, as long as you are *only* planning on using them to show the 'visible' edge of a curved surface. This is actually a question I've been meaning to ask around here, Have type5 lines been (...) (22 years ago, 17-Apr-02, to lugnet.cad.dev)
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