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Subject: 
Re: Hidden surface removal, and vertex order in part/primitive DAT files
Newsgroups: 
lugnet.cad.dev
Date: 
Sun, 3 Oct 1999 02:42:50 GMT
Viewed: 
613 times
  
Jean-Pierre PARIS wrote in message <37F660FB.1EC77AC9@wanadoo.fr>...
For example, if you take a 'bad' box made of 6 faces that have holes
beween them, your algorithm can lit an inside face. And in some parts,
such a situation exists. Thus my first too that tries to suppres these
holes, which came after rounding coordinates numbers


I see where you're coming from now.  You're right.

Assuming (after all close vertices are matched up) that no polygons have
zero neighbors, after determining the orientation of one polygon, you • could
visit each neighboring polygon (somewhat like a flood fill algorithm) and
determine its orientation easily.  Only one ray would be needed in the
entire process.

I have coded this flood fill algo. The main problem has be mentioned
above: for some reason, all parts are not made with matching edges. For
example, the studs primitive simply sits on the box5. In other parts,
one can encouter rounding pbs...


It's starting to sound like user intervention would be needed in most, if
not all, cases.

Maybe it would be simpler to just manually set the vertex order of the first
polygon, let the program fix that polygon's neighbors and its neighbors'
neighbors, and if any polygons are left then ask the user to set the vertex
order of one of those remaining, and repeat the process.

There are only 1600+ part files, after all...we could use a group of
volunteers to divide the task, and get every part fixed in a week's time. :)

-Gary



Message has 1 Reply:
  Re: Hidden surface removal, and vertex order in part/primitive DAT files
 
(...) I really don't like programs that need user interactions for such job! Thus I tried to cast enough rays so that all the faces are being oriented correctly. Now all the std bricks are OK, without any assumption about the fact that they are (...) (25 years ago, 3-Oct-99, to lugnet.cad.dev)

Message is in Reply To:
  Re: Hidden surface removal, and vertex order in part/primitive DAT files
 
(...) Sorry, but I think that the even/odd algorithm only work on 'correct' solids. For example, if you take a 'bad' box made of 6 faces that have holes beween them, your algorithm can lit an inside face. And in some parts, such a situation exists. (...) (25 years ago, 2-Oct-99, to lugnet.cad.dev)

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