Quad to triangles - Polyloop

pavroza · 30th December 2006, 23:14

Hi All,

I've just downloaded Hexagon 2.1 and giving it a try. It looks very nice by the way.

My question is:

Can I convert a FLAT quad into 2 triangles? ONLY TWO triangles I mean.

In the "Vertex Modelling" tools:
I've found the "Diamond tesselation" that converts quads to diamonds...
I've found the "Triangle tesselation" that converts quads to 4 triangles, NOT 2 triangles...aghh...

And in the "Utilities" section:
I've found a tool to "Triangulate non planar facets"...NOT MY CASE!!
and another one to "Triangulate n-gons" , that triangulates facets with
5 or more vertices, but NOT quads

The tools I've mentioned before create lots of triangles I don't need to
convert simple 3D models to triangles and use then in real time programs.

Thanks in advance,

Couerl · 31st December 2006, 07:48

I'm curious, why woud you want to convert all your nice clean quads into triangles?

The obvious way to me would be to export as an .obj and import it to whatever you are going to import it to? :|

Piem · 31st December 2006, 10:06

There is at least one reason ..Maxwell-Render. (it doesn't support real quads..too bad

)

It could be nice to export tris, at leisure.

And also, it could be nice to export dxf as quads, because those particular quads are read as tris by Maxwell

are · 31st December 2006, 10:57

Try the decimate tool in utilities tab but set for 1.00 - my quick tests show that it appears to work ?

pavroza · 31st December 2006, 12:53

Hi, thank you for your replies.

Yes, it looks like "decimantion" with 1.0 values could do that task. It makes
triangles for all quads in an object. I would prefer all the triangles to be generated the same way for all quads (always from the upper left corner to the lower right corner of the quad or from the upper right corner to the lower left corner) but it could be ok. Thanks again!

As regards the previous question about why I wanted triangles and not
quads:

I want my models to use triangles because I want to make 3D models for
real-time applications (mostly video-games and simulation).
Quads are a "compact" way of transferring information to the video card but they also have a big problem: many 3D engines need triangles.

Non-flat quads (when the 4 points are not located into a single plane) ,
or concave quads (when two edges make angles bigger than 180) coud generate visualization artifacts wrong colour distribution or not be seen at all (low level APIs like OpenGL require to tesselate non-convex shapes)

And finally...what's the best shape to approximate the shape of a triangle??
a quad? or a triangle?

hehehee (just joking).
Triangles are equivalent to pixels in 2D, the minimal shape from what you
can build every object you can imagine.

Perhaps my needs are a bit specific, I don't make nice organic models with
subdivision surfaces

Well, thanks again to everybody!

Thomas · 31st December 2006, 13:17

Quote:

Originally Posted by pavroza

I would prefer all the triangles to be generated the same way for all quads (always from the upper left corner to the lower right corner of the quad or from the upper right corner to the lower left corner) but it could be ok.

Yes, all the cut should be in the same way, you are true, but to answer to your comment about the '"upper left corner to the lower right corner" : how the software can know where is the first corner to start (I mean upper left corner). your eyes are seeing it, but the software don't have eyes are us ;)
Then, all of this to tell that having all the triangulation in the same way is easy, but always in the same direction is almost impossible

pavroza · 31st December 2006, 14:41

Yes, you're right, a computer has no "eyes" to see what's "up" or "down", although I don't know if the inner data structures of hexagon order the vertices in a consistent way that would allow to "classify" the vertices and make a coherent quad to triangles decomposition.

To reply that question we should be able to take a look at the source code of Hexagon (but Hexagon is not open source...so....) hehehehe...

A developer of hexagon could give a good answer. Sure!.

I've seen programs that have options to "flip" the triangle decomposition of quads too, perhaps that's an option for future Hexagon's versions (if any).

Non-coherent quad to triangle decomposition is good in some cases,
when you want to get nicer images under certain conditions.
See the book "Real Time Rendering" pages 269-274, 1st Edition by Tomas Moller and Eric Haines . ISBN 1-56881-101-2 , published by AK Peters.

Coherent quad to triangle decompositions is good in other like storing the
information in a compact way to render it extremly fast.

medeamajic · 1st January 2007, 03:49

Great info guys. I found this thread to be intersting. I did not know games needed to have trianlges. I want to get into gaming but it will have to wait until next year sometime. It looks like Hexagon should work for gaming.

Have any of you made any video games? Did you use Carrara, Hexagon, Lightwave, 3DS Max or Maya?

pavroza · 1st January 2007, 06:05

Yes, I have worked some years ago for Ubi Soft, as videogames programmer.
Now I work making the visual software of simulators (military and non military) and software tools to help to program this kind of software.

As regards videogames and simulators (or any kind of real-time 3d graphics)
triangles are the basic primitive for all kind of models. Quads too if your
3D engine can use them and you take care of non-flat and non-convex quads.

But perhaps this subject falls out of the original subject of this thread, and we should start a new one to talk about that, and not drive the users of the forum crazy

hehehehe.

LoneGunman · 1st January 2007, 06:19

Quote:

Originally Posted by pavroza

...I've seen programs that have options to "flip" the triangle decomposition of quads too, perhaps that's an option for future Hexagon's versions (if any)...

Hmmm, I was under impression that any 3D modeling software can do just that, if you do not like direction, just flip normals, triangulate, and then flip normals again, beauty of it you can do it for entire object or selected part of the mesh...

But, again, I might be wrong (been there before)

Shonner · 1st January 2007, 11:54

Quote:

Originally Posted by pavroza

Can I convert a FLAT quad into 2 triangles? ONLY TWO triangles I mean.

Export your model in 3DS format.

pavroza · 1st January 2007, 14:02

Thank you for all your advices

are · 1st January 2007, 16:39

I know silo has a "spin edge" function which might be worth looking at ?

after the decimation you can always (backspace) delete any edges that you wish to flow in the other direction and then connect the correct points (hotkey x). Might take too long though ?

laughingnome · 2nd January 2007, 19:30

Silo 2 also has subdivide which converts quads to tris

stu

30th December 2006, 23:14	#1 (permalink)
pavroza Vertex Join Date: Dec 2006 Posts: 5	Quad to triangles Hi All, I've just downloaded Hexagon 2.1 and giving it a try. It looks very nice by the way. My question is: Can I convert a FLAT quad into 2 triangles? ONLY TWO triangles I mean. In the "Vertex Modelling" tools: I've found the "Diamond tesselation" that converts quads to diamonds... I've found the "Triangle tesselation" that converts quads to 4 triangles, NOT 2 triangles...aghh... And in the "Utilities" section: I've found a tool to "Triangulate non planar facets"...NOT MY CASE!! and another one to "Triangulate n-gons" , that triangulates facets with 5 or more vertices, but NOT quads The tools I've mentioned before create lots of triangles I don't need to convert simple 3D models to triangles and use then in real time programs. Thanks in advance,

31st December 2006, 10:06	#3 (permalink)
Piem Booh! Join Date: May 2003 Location: Rennes/fr Posts: 6,644	There is at least one reason ..Maxwell-Render. (it doesn't support real quads..too bad ) It could be nice to export tris, at leisure. And also, it could be nice to export dxf as quads, because those particular quads are read as tris by Maxwell __________________ - Sheik Yerbouti - Let love the Noise technimesh.com Last edited by Piem; 31st December 2006 at 12:16. Reason: Sig

31st December 2006, 10:57	#4 (permalink)
are AKA RamPackWobble Join Date: Dec 2005 Location: Anglesey, North Wales, UK Posts: 216	Try the decimate tool in utilities tab but set for 1.00 - my quick tests show that it appears to work ? Attached Thumbnails Last edited by are; 31st December 2006 at 11:06. Reason: added picture

2nd January 2007, 19:30	#14 (permalink)
laughingnome stu Join Date: Mar 2004 Posts: 909	Silo 2 also has subdivide which converts quads to tris stu __________________ just trying to cut down the pain threshold AMD2.4 dualcore 4 gig ram, 9400GT ,WinXP Home

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31st December 2006, 07:48	#2 (permalink)
Couerl Polygurbs Join Date: Jul 2005 Location: Denver Posts: 1,301	I'm curious, why woud you want to convert all your nice clean quads into triangles? The obvious way to me would be to export as an .obj and import it to whatever you are going to import it to? :\|

31st December 2006, 12:53	#5 (permalink)
pavroza Vertex Join Date: Dec 2006 Posts: 5	Hi, thank you for your replies. Yes, it looks like "decimantion" with 1.0 values could do that task. It makes triangles for all quads in an object. I would prefer all the triangles to be generated the same way for all quads (always from the upper left corner to the lower right corner of the quad or from the upper right corner to the lower left corner) but it could be ok. Thanks again! As regards the previous question about why I wanted triangles and not quads: I want my models to use triangles because I want to make 3D models for real-time applications (mostly video-games and simulation). Quads are a "compact" way of transferring information to the video card but they also have a big problem: many 3D engines need triangles. Non-flat quads (when the 4 points are not located into a single plane) , or concave quads (when two edges make angles bigger than 180) coud generate visualization artifacts wrong colour distribution or not be seen at all (low level APIs like OpenGL require to tesselate non-convex shapes) And finally...what's the best shape to approximate the shape of a triangle?? a quad? or a triangle? hehehee (just joking). Triangles are equivalent to pixels in 2D, the minimal shape from what you can build every object you can imagine. Perhaps my needs are a bit specific, I don't make nice organic models with subdivision surfaces Well, thanks again to everybody!

31st December 2006, 14:41	#7 (permalink)
pavroza Vertex Join Date: Dec 2006 Posts: 5	Yes, you're right, a computer has no "eyes" to see what's "up" or "down", although I don't know if the inner data structures of hexagon order the vertices in a consistent way that would allow to "classify" the vertices and make a coherent quad to triangles decomposition. To reply that question we should be able to take a look at the source code of Hexagon (but Hexagon is not open source...so....) hehehehe... A developer of hexagon could give a good answer. Sure!. I've seen programs that have options to "flip" the triangle decomposition of quads too, perhaps that's an option for future Hexagon's versions (if any). Non-coherent quad to triangle decomposition is good in some cases, when you want to get nicer images under certain conditions. See the book "Real Time Rendering" pages 269-274, 1st Edition by Tomas Moller and Eric Haines . ISBN 1-56881-101-2 , published by AK Peters. Coherent quad to triangle decompositions is good in other like storing the information in a compact way to render it extremly fast.

1st January 2007, 03:49	#8 (permalink)
medeamajic Now, I learn animation Join Date: Sep 2005 Posts: 1,028	Great info guys. I found this thread to be intersting. I did not know games needed to have trianlges. I want to get into gaming but it will have to wait until next year sometime. It looks like Hexagon should work for gaming. Have any of you made any video games? Did you use Carrara, Hexagon, Lightwave, 3DS Max or Maya?

1st January 2007, 06:05	#9 (permalink)
pavroza Vertex Join Date: Dec 2006 Posts: 5	Yes, I have worked some years ago for Ubi Soft, as videogames programmer. Now I work making the visual software of simulators (military and non military) and software tools to help to program this kind of software. As regards videogames and simulators (or any kind of real-time 3d graphics) triangles are the basic primitive for all kind of models. Quads too if your 3D engine can use them and you take care of non-flat and non-convex quads. But perhaps this subject falls out of the original subject of this thread, and we should start a new one to talk about that, and not drive the users of the forum crazy hehehehe.

1st January 2007, 14:02	#12 (permalink)
pavroza Vertex Join Date: Dec 2006 Posts: 5	Thank you for all your advices

1st January 2007, 16:39	#13 (permalink)
are AKA RamPackWobble Join Date: Dec 2005 Location: Anglesey, North Wales, UK Posts: 216	I know silo has a "spin edge" function which might be worth looking at ? after the decimation you can always (backspace) delete any edges that you wish to flow in the other direction and then connect the correct points (hotkey x). Might take too long though ?