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Hello, I'm still somewhat new to the world of 3d graphics and from many of the resources I've read, it suggests to model meshes with triangle polygons since most API's will convert quads and such to triangles anyways. However, my artist friend tells me its much easier to model using quads and some of the meshes I've seen are build from quads. Can anyone tell me the pros and cons of each and what the industry standard is? Also, would anyone know where I could find a polygon count and perhaps any other model info for character models for any modern commercial games (e.g. half-life 2, doom 3, world of warcraft... anything 3d) Thanks!

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I'm not terribly experienced, but I believe high poly work is usually done with quads to have subdivision work properly. For games and such, every triangle matters.

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EVERYTHING is rendered as triangles in realtime engines. Graphics cards only render triangles. Quads are rendered as two triangles like so:

*------*
| /|
| / |
| / |
*------*

If your friend was to export his mesh in a realtime-rendering friendly format, all of his quads would be converted to triangles before rendering.

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Everything may be exported as triangles in the end, but quad-based models look best and are easier to work with. Shading is a lot smoother and you get less jitter along the contours, for example when you rotate the model in realtime. Also, when skinning a triangular model you get unpredictable skin behaviour because the vertices are randomly aligned. This is also the problem when editing; edge- and vertex operations are harder to do and give unpleasing results. These problems get bigger as the polycount drops.

On a nearly finished model you could chip off some polygons by triangulizing small or obsolete quads, and sometimes a specific part of the mesh is better suited to be tris even. But in general you should always try to retain as much quads as you can. The amount of vertices you save by doing everything in triangles is neglectable and vertex count isn't big of a problem on graphics hardware anyway.

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Everything you throw at the graphics card will be converted to triangles.
Because a quad can be converted to 2 triangles in 2 ways your artist should do that conversion to make sure the result of the conversion is as expected. Your artist can still model the whole thing using quads and then convert it to triangles afterwards. After that conversion he should search the mesh for splits that just don´t fit and fix them.

The problem is, that a quad does not need to be planar. Just imagine a quad:
A-----B|     ||     ||     |D-----C

Now leave B and D on height 0 and pull up A and C (fold a piece of paper diagonally). Splitting that quad can result in two different shapes. If you split it along BD you will get some kind of \/ shape along that diagonal, splitting along AC will result in /\ shape. So in a case like that it´s obvious that controlling how the quad is split is a good thing (especially in rather detailed areas like a face or something like that). In case you wonder whether a player will notice anything like that on a character model: He will, because that difference can screw up the lighting quite badly as it also influences the interpolation of the normals between vertices.
If the quad is planar it doesn´t matter how it is split, the results should be the same, so your artist could just model with the restriction that every quad has to be planar and leave the mesh like that, but I think modelling with that restriction would be rather painful.

I got no proof what the industry standard for games is, but I would assume they´re using triangle meshes just for the above reason.

Don´t know if this is correct, but AFAIK Half-Life 2 uses something between 2500 and 7000 polygons for their character models.

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