BorlandTalk.com Borland discussion newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Sorting 3d triangle points around normal to be anticlockwise          BorlandTalk.com Forum Index -> Delphi Graphics View previous topic :: View next topic   Author Message Paul Nicholls Guest Posted: Wed Apr 21, 2004 3:02 am    Post subject: Sorting 3d triangle points around normal to be anticlockwise Hi all, I was wondering how I can sort the vertices of a 3d triangle relative to a normal so they are anticlockwise around the normal? I have tried googling, but no luck so far... Thanks in advance, Paul Nicholls (Delphi 5/6 Professional) "See No Evil, Hear No Evil, EMail No Evil !" - Paul Nicholls [email]paul-nicholls (AT) hotmail (DOT) com[/email] Replace '-' with '_' to reply Back to top Eric Grange Guest Posted: Wed Apr 21, 2004 7:48 am    Post subject: Re: Sorting 3d triangle points around normal to be anticlock Quote: Hi all, I was wondering how I can sort the vertices of a 3d triangle relative to a normal so they are anticlockwise around the normal? Compute the triangle's plane normal with a cross product, then compute the dot product of that normal vs your reference normal, if the result is negative, you have to invert the order of the vertices. Eric Back to top Paul Nicholls Guest Posted: Thu Apr 22, 2004 12:21 am    Post subject: Re: Sorting 3d triangle points around normal to be anticlock Thanks Eric, I came up with this myself last night! <G> Thanks though :-) Cheers, Paul. "Eric Grange" <egrange (AT) glscene (DOT) org> wrote Quote: Hi all, I was wondering how I can sort the vertices of a 3d triangle relative to a normal so they are anticlockwise around the normal? Compute the triangle's plane normal with a cross product, then compute the dot product of that normal vs your reference normal, if the result is negative, you have to invert the order of the vertices. Eric Back to top Emi Guest Posted: Thu Apr 22, 2004 3:49 pm    Post subject: Re: Sorting 3d triangle points around normal to be anticlock i had the same trouble a few months ago, opening DXF files with wrong normals. i'm curious.. was this the case? "Paul Nicholls" <.> wrote Quote: Thanks Eric, I came up with this myself last night! <G Thanks though :-) Cheers, Paul. "Eric Grange" news:40862686$1 (AT) newsgroups (DOT) borland.com... Hi all, I was wondering how I can sort the vertices of a 3d triangle relative to a normal so they are anticlockwise around the normal? Compute the triangle's plane normal with a cross product, then compute the dot product of that normal vs your reference normal, if the result is negative, you have to invert the order of the vertices. Eric Back to top Paul Nicholls Guest Posted: Thu Apr 22, 2004 11:07 pm    Post subject: Re: Sorting 3d triangle points around normal to be anticlock No, I'm trianglulating points in 3d space and I had normals of triangles that should have been facing in the opposite direction so I had to check and sort the points if necessary... "Emi" <emisosa_dot_hotmail_dot_com> wrote Quote: i had the same trouble a few months ago, opening DXF files with wrong normals. i'm curious.. was this the case? "Paul Nicholls" <.> wrote Thanks Eric, I came up with this myself last night! <G Thanks though :-) Cheers, Paul. "Eric Grange" news:40862686$1 (AT) newsgroups (DOT) borland.com... Hi all, I was wondering how I can sort the vertices of a 3d triangle relative to a normal so they are anticlockwise around the normal? Compute the triangle's plane normal with a cross product, then compute the dot product of that normal vs your reference normal, if the result is negative, you have to invert the order of the vertices. 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