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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Thu, 18 Apr 2002 01:21:28 GMT
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Viewed:
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486 times
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In lugnet.cad.dev, Kyle McDonald writes:
> Well, I believe that there is something called a 'Z offset' that can
> be used not to actually move the geometry, but to make sure the lines
> appear 'on top' of the faces.
That sounds like glPolygonOffset which would be part of the solution
because it allows the edges to look clean. We all use that already.
> I have some Java3D code, and sample pics that were done using
> this technique. I can mail them to anyone interested, but I don't
> think it would be nice to send them to the whole mailing list. The
> object in the pics is basically one large mesh (array of strips?)
> The pics show that the outlines are drawn on the fly for the shape as
> the viewing angle changes.
>
> I still don't have the geometry setup in strips and fans enough to
> try to see if this will work for me or not. I expect that it may
> remove some of the edges, but it may also prove impossible to stripify
> all the polgyons that need to be (without inlining them on the fly)
> and therefore we may end up with undesirable lines where a fan meets
> a strip, etc.
I can see how you might accomplish some of that by manipulating
glEdgeFlag when you define your strips, and then redrawing with
GL_POLYGON_MODE set to GL_LINE, but I still don't see how it
produces the equivalent of type 5 lines. Maybe if you get the
stencil buffer involved? Beats me...
Don
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Message has 2 Replies:
 | | Re: Why Type 5 Lines?
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| (...) Yeah, the stencil buffer, that's gotta be it. If you've got BFC working then you can use the stencil buffer to count how many times an edge is draw in GL_LINE mode. Edges on back facing triangles won't be drawn, so you'll only count one edge (...) (22 years ago, 18-Apr-02, to lugnet.cad.dev)
| | | Re: Why Type 5 Lines?
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| I was reading through this more, and while I still don't know exactly how it all works, I think I stumbled onto something. > I dont know how many of you have come across this technique before. I > remember finding an OpenGL demo that did this kind (...) (22 years ago, 18-Apr-02, to lugnet.cad.dev)
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Message is in Reply To:
| | Re: Why Type 5 Lines?
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| (...) Well, I believe that there is something called a 'Z offset' that can be used not to actually move the geometry, but to make sure the lines appear 'on top' of the faces. Before I go more into this I need to back up a bit. I currently use the (...) (22 years ago, 17-Apr-02, to lugnet.cad.dev)
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