retopo in blender 2.5

[michaelw]

this is a brief tutorial about re-topologising in blender...

it's not step by step, but might be of use.... I'll expand depending on peoples needs...

1: First export your model as an obj from sculptris

2: import obj into blender 2.5.

2.5 these days should work by default for both, but 2.49 will require non default import options:
NB the defaults are fine UNLESS you have mapping data from paint mode... if you do you MUST enable objects and groups...

3: add another object that will be the basis for our new topology (a plane will be fine)

4: with that object selected enter edit mode (via the 3d view header or hit "tab")

5: enable snapping, face mode and projecting onto the background geometry in the 3d view header bar:



in the above illustration you can see the finished "cage object"

This was built by selecting edges of the original plane object and extruding them over the surface of the model... the "snap" mode conforms those edges to the background model.

that was pretty much it barring some pulling vertices around and making some faces by selecting two edges and hitting "f"

that's all really!

you'll need to know what constitutes "good" animation geometry, edge loop theory etc etc...

I suggest checking out the subdivision modeling website:
www.subdivisionmodeling.com/forums/

and the primer:
web.archive.org/web/20061118062010/www.subdivisionmodeling.com/wiki/tiki-index.php

Whilst doing the above it's a good idea to be able to check how well the cage will work subdivided, also if the model is symmetrical a "mirror modifier" will help.

so

6: in the "properties" region go to the "modifier" tab.... add a "multires" modifier ("a subsurf" modifier will work too, but multires will allow further sculpting in blender's own "sculpt mode").
Enable "optimal draw" and subdivide a few times... You'll probably want to use the "preview" slider a lot to toggle up and down subdivision levels in object mode as you go.

7: if the model is symmetrical add a "mirror" modifier.... the "clip" button makes the mirror plane sticky and stops penetrating the other side



8: to make the generated subdivisions "stick" to the underlying geometry add a "shrinkwrap" modifier... The target should be the obj object that you imported.....
change the mode from "nearest surface point" to "project" and "enable" direction to negative and positive....

the right hand column shows the base cage and all the modifiers....


now, you can "tab" back and forth from edit mode to object mode and see exactly how good your retopo is!

subdivided once with multires....




subdivided twice... note how the generated loops fit to teh target mesh with shrinkwrap



keep going until all the detail from your sculptris mesh is "captured"


you may want to go the " object" tab and enable "wire" to draw over your cage model... if you've selected "optimal display" in your "multires modifier" you should get a clear view of the edge loops and whether they follow your topology nicely or not


finally, when happy, you *should* be able to "apply" the shrinkwrap modifier to your object and turn off all teh snapping... from here on it's as if you sculpted it natively in blender and you can subdivide it some more, detail up with blender sculpt whatever....

... or just add an armature and rig it up to animate!

I know this probably requires a lot of advanced knowledge of blender and what good topology is, but maybe it helps! let me know and I'll endeavor to improve this tutorial!


I can do a follow up for transferring mapping and sculptris bump and colour maps to the new model too if anyone's interested.

[wasa]

I think a follow up would be excellent ;D

[michaelw]

Ha, give me a few days and I'll sort it out!

[sanc]

Awesome, i only knew the basics of the retopo on 2.49b that i applied one some sculptures already and had no idea how usefull the shrinkwrap would be.
Thanks a lot, it will clarify some points for me.

[denny]

This is awesome, I'm going to work more with Blender in the future and will definitely try this out for my sculpts.

[marvolo]

Could you keep the first (lowpoly) mesh and bake the normals from the sculpt? How good would the results be?

[sanc]

In Blender you can bake normals from the sculpture into the retopo.

My retopology of a sculptris model next to each other :



And the retopo with the baked normals from the sculpture , next to the sculpture itself :

[wikkidwidgets]

Very nice gentlemen!

[nezumi]

michaelw - thx a lot for that retopo in Blender explanation. Exactly what I was looking for and works like a dream.
OK, so now is time for little follow up, if you please..

[michaelw]

Jun 16, 2010 23:49:12 GMT 1 marvolo said:

Could you keep the first (lowpoly) mesh and bake the normals from the sculpt? How good would the results be?

my really low model doesn't quite have enough of a silhouette for that... for a video game I'd probably add a few more loops around the shoulders for example, or just use it subdivided once (though that's slightly heavy still....even with todays game budgets!) as you can see by SANC's post if the silhouette has enough detail, the normal map is good for rendering the details.

an alternative workflow for pre-rendered would be to use a subdivision surface modifier in combination with a displacement modifier to get the silhouette right and forget shrinkwrap.... then use either bump or normal maps for the higher frequency details.

this is the approach I usually take when a model is completed.... but the work-flow I described above in the original post is good if you want to "tweak" your sculpt in blender sculpt mode.

This should also be covered in a follow up!

Wikkidwidgets, I'll make a PDF when done with teh Q and A, but it sounds like there's lots still to cover!

[michaelw]

ps, sanc, that's cool, but your topology around hips and shoulders will probably not deform too well! (but mine has issues in the arm pits!)

[thwak]

Thanks a bunch for this!

[sanc]

Jun 17, 2010 5:57:37 GMT 1 michaelw said:

ps, sanc, that's cool, but your topology around hips and shoulders will probably not deform too well! (but mine has issues in the arm pits!)

Yes, i noticed when i tried to rig it

But that was my first retopo after reading a simple tutorial, it was bound to have beginner mistakes as i was not really knowing what i was doing in term of edge flow and junctions.

Fortunately, those mistakes served very well for a learning session as it allowed me to understand better how to build better the body junctions to avoid horrible deformation for animating.
That's why i like Blender, as it makes it easy to edit your topology after rigging and posing, and then see the impact of of your model modification on a pose in real time.

It helps a lot in figuring it what topology works better for the body junctions (hip/shoulder/neck/fingers/etc..)

Additionally, all those mistakes on the retopologized model helped a lot to understand better how weight painting could be tweaked to "help" the deformation to become smoother.

originally, with all the badly thought edge flow, posing it was leading in those kind of shoulders problem, as you pointed it would be :


After tweaking the topology and weight painting on the fly while learning from those mistakes, i was able to get it a bit better for the shoulders


For me it was a very interesting learning session, as those mistakes allowed to learn some other Blender tools in a different way.

[michaelw]

Sanc, Awesome progress! It's like one of those "body building" ads.... here's me after just 4 weeks on xbrand protein shakes! with a face palm thrown in!

[markjoel60]

Not to hijack the thread (which is really useful -- THANKS Michael!) but there are many different approaches to getting tricky areas like the shoulders right. Good edge flow cannot be over stated, but you can also correct it with blend shapes (Shape keys in blender). There are some great scripts in Blender to facilitate this. You can sculpt the mesh the way you want it -- to correct the edge flow -- and then create a shapekey for it. Then you can have that shape key applied automatically as an IPO driver.

Here is a great resource for modeling for articulation. The author is a TD at Pixar... so he knows a thing or two about this subject!

www.hippydrome.com/