MD 4 Quads

[VulpesVulpes666]

I am wondering if someone could explain me the advantages of using quads over tris in mesh rigging,weighting or baking processes,other words what can you do with quads that you can't with tris?

[Cathy Foil]

There are many benefits to using quads over triangles.  MD or Marvelous Designer triangles are in a very random pattern.  The quad conversion in MD 4 is not all that much of an improvement because it doesn't have that good of edge flow.

I tested MD 4 extensively during the beta tests.  I was most interested in how well the new quad conversion or triangulation feature worked.  I was pretty disappointed.  I was hoping I wouldn't have to continue to retopo MD mesh in Maya.

OK think of the random triangular pattern like clothes being made out of aluminum foil.  When the mesh bends at the joints it doesn't bend that well.  When quad mesh bends, provided it has good edge flow, it bends much more naturally because the edge flow creates creases there they would naturally be in real clothes.  Plus if you look closely at MD mesh in SL that is straight from MD and still triangles the light reflects off the surface with sort of a mottled pattern.  That is because the Normals are all sort of random because of the random pattern verses the nice grid like pattern of quads that have a good edge flow.

As for rigging quads, with good edge flow, are easier to adjust the weights.  Each vertex on say a horizontal edge loop will be weighted more or less the same or at least in an easier to figure out weight pattern than the random pattern of MD random triangles.  Think of it this way.  Which surface would it be easier to paint a nice even perfectly symmetrical checkerboard pattern on.  A grid made up of random triangles or a nice evenly spaced quad grid pattern?  The quad pattern of course.

Lastly quads, with good edge flow, are just so much more efficient than the random triangle pattern from MD or even their new quadrangulation conversion.  When I retopo MD triangles into quads with Maya my quad version is usually about half or just over half  the number of vertices as the original MD mesh of random triangles.

To sum it up quads are:

1. The mesh bends at the joints better.
2. Light reflect off quads better because of nice even normal distribution.
3. Easier to rig and adjust the weights because of the even grid like pattern they make.
4. More efficient because you can use few vertices and still have the mesh look as good as the MD triangles.
5. Almost forgot because you end up using fewer vertices you have fewer vertices you have to rig and adjust the weights of.

I have a couple of YouTube videos I made on how to retopo MD mesh into quads using Maya.  So I am very familiar with MD and the benefits of quads.

I hope the helps.
Cathy

 

[VulpesVulpes666]

Thank you for the explanation,now i totally understand:matte-motes-nerdy:

[Nalates Urriah]

When you import a mesh to Second Life, the SL system will turn quads into triangles. Press Ctrl-Shift-R to see the mesh layout within SL.

To have control over how the quad is broken into triangles, you need to create your triangles before uploading to SL. You don't have to do every quad in the item. Just those where you need to control how the mesh bends at joints.

[Cathy Foil]

Nalates is right.  Upon uploading your DAE file to SL if you have not already triangulated your quad mesh it will automatically be triangulated.  She is also correct in that when you retopo a MD or any random triangular mesh created in other programs such as Zbrush or 3D Coat into quads the entire new retopo mesh dosen't have to be entirely made of quads.  It is just best to keep the triangles to a minimum.

When you triangulate a quad mesh an edge is inserted between two opposite corners of  the quad making two triangles.  These two new triangles tend to be more coplanar than random triangles created in MD and other programs.  Copanar means two faces lying on the same plane.

Most of the time I find that I don't need to triangulate my mesh before I upload it to SL.  But there are times when you want and need to triangulate your mesh first.

Say you made a mesh shirt and an you want both sides to be perfect mirrors of  each other so they move and bend in the exact same way.  What you would want to end up with is the quads on each half being into triangles in different directions.  Say on the left half of the shirt you want the quads split from bottom right vertex to top left and the right half of the shirt quads split from bottom left to top right.

Here is an excellent page on why model with quads: http://blog.digitaltutors.com/modeling-quads-triangles-use/

[Jake Koronikov]

Below another example about how to use tris. This is a quite low-poly shirt kind of a model. With both sides visible, the model has 792 faces (1580 tris).

There are two small triangles on the shoulder area (only the front tri is visible in the photo below, the back tri is at the same location behind the body). The purpose of those little tris is to "sub-divide" only the very shoulder area quads. This  helps to reduce blockiness in the final user experience. We do not need to subdivide the whole edge loop around the body, only a short distance between shoulder front and shoulder back.

The illustration below clarifies this.

Other advantages of quads in this case:

* Very easy to UV-unwrap

* Very easy weight painting process due to natural edge flow (almost like human muscles)

* Very smooth final appearance inworld.

This model could be made even with a lot less faces, but to achieve good fitted-mesh results, we need some extra edgeloops on belly, arms and so on.