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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Fri, 19 Apr 2002 21:50:39 GMT
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Viewed:
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671 times
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In lugnet.cad.dev, Travis Cobbs writes:
>
> I understand what you are saying, but it won't happen that way if Z buffer
> writing is enabled during the drawing of the transparent surfaces. The
> transparent surfaces aren't really transparent. They're just blended with
> whatever is behind them. (This is why you get interesting effects if you
> don't sort them.) They look like they are transparent, but if they really
> were transparent, then you wouldn't have to sort; you could just draw them
> in any order and they would look correct. The reason they have to be sorted
> is that the blending only occurs with whatever is drawn before them.
>
> So, if you turn on Z buffer writing while drawing the transparent surfaces,
> then the back sides of the wireframe won't show up as long as Z buffer test
> is enabled when drawing the wireframes. The back-facing wireframe is drawn
> after the filled transparent surfaces. The edges will still show up because
> those particular lines will pass the Z test. (Polygon offset will still
> probably be needed to get clean lines.) This is actually exactly the same
> thing that happens with the opaque surfaces. The key reason it will work
> with transparent surfaces also is the fact that they aren't really
> transparent; they're just blended with whatever is there before them.
>
> Normally you don't bother to enable Z buffer writing when drawing the
> transparent surfaces, because they are the last thing drawn, and it won't
> matter. However, it doesn't hurt anything to enable it, other than slowing
> it down a little. And if you want to use this algorithm, it has to be enabled.
Thanks for that explanation, however I think we still need to include type 5
lines in parts, so that programs which don't implement this technique (eg
ldraw) can still display the curved edges correctly. Programs which do
implement it can simply ignore the type 5's
ROSCO
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Message has 1 Reply:
 | | Re: Why Type 5 Lines?
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| (...) Sorry, I never intended to imply that it should replace type 5 lines. In addition to the problem of backwards compatibility, this will only work for BFC-certified parts. --Travis Cobbs (tcobbs@REMOVE.halibut.com) (22 years ago, 19-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 understand what you are saying, but it won't happen that way if Z buffer writing is enabled during the drawing of the transparent surfaces. The transparent surfaces aren't really transparent. They're just blended with whatever is behind (...) (22 years ago, 19-Apr-02, to lugnet.cad.dev)
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