Retopology for games

Yerus

I wonder how to make a pretty good retopo for games, and I see that peolple use a lot of triangulation for optimization, but handicrafted in specific and proper areas. Take a look at this image for instance. How can one achieve this result? What’s the workflow to find where and how to build those tris?

Klunk

sorry but you need to explain it better, is this a picture of an in game retopology or the sort of model you'd like to to retopologize ?

musashidan

It's simply a matter of experience. Practical knowledge of silhouette/topology/deformation/shading/baking/optimisation. You learn to understand how all of this works together by building assets. There's no secret to it.

Mark Dygert

When you say retopologize, I think you mean modeling?

Retopo implies that you have a mesh that isn't ready to go into a game engine, usually you have a high poly-ish version that needs to be optimized and needs to deform well.

Really all you are doing when you retop is modeling over the top of an existing mesh. So there are tons of modeling tutorials all over the place.

Your main goals are:

• Accurately capturing the silhouette
• topology that supports smoothing and baking textures
• Topo that isn't grossly wasting tris while still being able to properly deform the mesh, which is largely dependent on the actions the character needs to take and their importance to camera/player.

So how you model that? It depends on what your goal is.
Are you modeling a base mesh to take it into a sculpting app like zBrush?
Are you skipping the baking process and going straight to game with hand drawn textures?
Factors outside of the modeling pipeline play a huge role also...
Is it for a mobile RTS, or a cinematic driven FPS on PC?
Will there be facial animation? Joints, morphs or both?
Does the rig have twist bones? How about secondary motion on hangy bits and pouches?
What is the tech budget of the game? Do environments take center stage? How many characters are on the screen? Is this a hero character or a throw away background NPC?
Can the character be customized? To what level? 

There are a ton of factors that weigh in on how you build a character and really retopo is just modeling. SOMETIMES you can get a way with an automated solution but that usually works best on static objects that don't deform, characters usually require more care and control.

Alex_J

 I think it's good to start by making traditional block modeled characters so you can learn these techniques first, rather than making a mess in zbrush and then trying to figure out how to clean it up.

These courses cover most of the tools you'd use to the do the work.:

https://www.pluralsight.com/paths/maya-character-modeling

Yerus

I already know how to retopologize, but not a animated game character.
So it's been said that there is an automatic way to build the tris, but it's only good applied
to static assets, othewise the triangles are built by handicraft only? 

My question was more about how the tris behave, and where should they be. And also
how (what angles, what placement, what order). If the answer is 'it varies', then it
depends on what? Can I build a huge tri upon a patch of quads almost without respecting
the vertices placement?

Neox

if you analyize your turntable up top, you will notice, that the tris are not random. they occur when larger / simpler surfaces need to be denser in order to have a smoother silhouette. there are areas where normalmaps easily can do the job and others where you need the geometry to build a denser surface. the tris here are just in the transitioning zones.

musashidan

What I touched on above, Mark Dygert explained in more depth. These are the key elements. All of these things have to work together:

Topology supports correct surface shading and baked shading

Topology is optimised and captures the silhouette.

Topology supports deformation when animated.

As mentioned, you must keep all of these things in mind when modeling and you can use any combination of tris and quads that support and compliment the guidelines above.

Your gif above has some good examples of strategically placed tris that capture the silhouette and optimise the vert count. Try and find more wireframes like this and study why the topology is the way it is, or rip meshes from games or UE4 samples and study them.

Yerus

All right then, thanks yall 4 the help! 
I think sometimes  (not the case of the gif) tris can be formed by the function of a denser mesh with a simpler one,
for instance the neck and the head, or by core edge loops/unarticulated area.
Cheers!