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View Full Version : Triangles: why are they so bad?


dreadpyrat
06-27-2005, 03:19 AM
I've jsut started my foray into high end 3d modeling for film and keep hearing that I should avoid having triangles at all costs. They seem unavoidable! I mean, there is only so much you can do to get rid of them...I always seem to end up with a few.

My question is: why are they so bad? Everyone tells me to not have them but no one sys why. Why is it such a sin to have them in high end meshes? Do they yield wierd rendering results?

Can someone explain this to me and further, some techniques for avoiding them? Thanks!

Rob

kuui
06-27-2005, 06:08 AM
first, all the smoothing stuff (let's called it subD's even if they're not real ones) doesnt work very well with triangles, they produce a bumpy and unclean surface. also triangles don't deform like you would expect while posing or animating.

on the other hand if you need small bumps on a surface, for example ellbow bones on a character arm, triangles could be your best friend. it's ok tu use them there.

models like cars on the other side require a perfect clean mesh, or you'll get realy ugly und wavy reflections and surface.

gjpetch
06-27-2005, 06:48 AM
The only way to get rid of a triangle is to feed it off (by creating or removing an edge) to another triangle, or a face with odd number of sides, or to an open edge.

So essentially two triangles can cancel each other out, once you've got that worked out its not so hard to stick to quads.

valoukh
06-28-2005, 03:50 PM
I have a couple of questions on this:

1) Would you ever slap a vertex along an edge just so there were enough around a hole for you to weld another object into it. E.g. a hole with 4 verts and an object with 5 verts? And if you did, would it be better to make the adjoining edge visible (spawning a triangle) or leave it hovering on the edge?

2) Do you tend to have edges going all the way around model, like the contours of a sphere? I.e. could you trace one line all the way around a human head, or does the mesh break up at, say, the nose?

Thanks,
-valoukh

Blikkie
06-28-2005, 11:03 PM
Why quads are good (using my WIP):

Quads:
http://druan.student.utwente.nl/%7Eremco/DoubleBodyStage1View10.jpg

Tri's:
http://druan.student.utwente.nl/%7Eremco/DoubleBodyStage1View11.jpg

Both models are effectively six times subdivided in Blender.

valoukh
06-29-2005, 08:16 AM
Eerr!

I heard someone say that it's advisable to have 99% quads. Would you consider it acceptible to have 1% triangles? In the past I've come across annoying little bits of a mesh where it's difficult to make a quad, and in these situations triangles are the only way out without rebuilding the entire thing. I've learned to model knowing to avoid the holocaust that is the 5-sided polygon, but sometimes it seems unavoidable to have triangles, especially with a symmetrical object. What do you think?

-valoukh

Blikkie
06-29-2005, 11:10 AM
If a triangle here and there is unavoidable, well, screw it guys and keep them. Usually it is quite possible to stuff them away in an easily overlooked corner and that is perfectly alright.

To quote a dutch song: wat je niet ziet bestaat niet.

Wiro
06-29-2005, 03:54 PM
It's no sin not to have all quads if it doesn't disrupt the smoothing. But try to avoid tris and let loops terminate to 5-sided polys instead. Just make sure you tuck it away somewhere safe.

valoukh:
1)
Leave it hovering but if you can, stretch the loop a bit further into the object with the 4 vert hole. If the loop terminates just where the two objects are welded together the sharp change of direction will smooth badly.

2)
If it doesn't clutter the mesh, yes all the way around. Otherwise try to change it's direction and lead the loop into a place that needs it. If all else fails, lead it to a neutral place and terminate it (making a 5 sided poly, not a 4 sided and a tri)

Wiro

PizzasRgooD
06-29-2005, 05:17 PM
If the triangle is on a flat part of the mesh then it doesn't make a difference, can't see any bumps then.

valoukh
06-29-2005, 07:58 PM
Wiro what do you means by "loops"? Is this poly-talk? I model with meshes! :(

-valoukh

yosri
06-30-2005, 06:05 AM
first, all the smoothing stuff (let's called it subD's even if they're not real ones) doesnt work very well with triangles, they produce a bumpy and unclean surface. also triangles don't deform like you would expect while posing or animating.

on the other hand if you need small bumps on a surface, for example ellbow bones on a character arm, triangles could be your best friend. it's ok tu use them there.

models like cars on the other side require a perfect clean mesh, or you'll get realy ugly und wavy reflections and surface.
this ok

thanks

Wiro
06-30-2005, 09:38 AM
Wiro what do you means by "loops"? Is this poly-talk? I model with meshes! :(

It's become a popular term to call a continuous line of edges a loop, even if it's not closed

Wiro

valoukh
06-30-2005, 09:42 AM
Oh, that's good to know. :)

Thanks Wiro.
-valoukh

StephanD
06-30-2005, 11:16 AM
first, all the smoothing stuff (let's called it subD's even if they're not real ones) doesnt work very well with triangles, they produce a bumpy and unclean surface. also triangles don't deform like you would expect while posing or animating.

I don't agree,triangles and n-gons are good,embrace them!


"Rules" state otherwise,but I don't like rules when I'm creating plus triangles and n-gons can in fact help you get a completely quaded-mesh output in the end,heheh.


Take for example,the said rules.

Triangles DO deform badly as their flat surface is only made of three points in space,that doesn't mean we can't use them efficiently,same wih N-gons.


A mesh that has triangles and n-gons and which respects "some" level of rules can easily be Subdivided with CC SdS and will become a full quad mesh,with poles no greaterthan 5 vertice.

I'm talking physically subdividing,not an SDS preview.

The usual rules would be not to have poles that exceeds 5 vertice/edges/polygons.

With that in mind,you just have to be careful not to let two n-gons next to each other or next to a triangle,same thing for the latter.After subdivision,you'll only end up with "politically correct" poles.

EDIT:Sorry,forgot one important rule for this...Never,ever subdivide an n-gon greater than 5 faces,it would result in a 6+ vertice pole.

Hope this helps

JuddWack
06-30-2005, 05:13 PM
Whats better to have:

Triangle
or
A vert that connects 5 quads

Shonner
07-04-2005, 06:56 AM
I got into the habit of modeling with quads. Then I found out that Vue 5 Infinite doesn't support quads.

OptimusDinkus
07-04-2005, 09:12 AM
the thing about quads is there nice to solidify forms such as the meat of muscles, but tendons and other things like creases and such tri's can be very helpfull. I just depends on what looks right in the end as usual

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