Postwork: Challenge of dealing with cloth intersections
RenderPretender
Posts: 1,041
Hello -
I was wondering how folks here choose to address situations such as when a character is kneeling or sitting on a cloth item such as a blanket, towel, or sheet, and the folds or wrinkles in the latter intersect with the character in an unnatural way (intersection). I try to minimize that with posing/positioning, but ultimately end up having to clone and paint a more natural looking intersection in postwork, since morphing the sheet, etc., is not always possible.
I'm curious to know how others address this issue.
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A few ways:
- Turn on smoothing for the cloth and set collision item to the character. In params, increase the collision/smoothing iterations as needed.
- d-Formers (or the new Mesh Grabber product) can be used to move cloth areas that are a bit too deeply intersected for smoothing alone to handle.
- If either of the above get it close, I'll often hide the 'bone' of the character covered by the cloth to eliminate the possibility of poke thru.
- If hiding the bone is too drastic, I'll use geometry editor to select some faces of the character and hide them (note, this doesn't save with the scene so have to hide and render).
- Can also add a push modifier to the cloth, though I find this can be a problem if I 'push' too much since it affects the entire object, not just the part you want to fix.
- Can render twice. Once with character or bone hidden. Once without. Then merge in post by layering the two images and using eraser. I like this better than clone brush since it looks more natural.
These are excellent suggestions. Here are a couple additional refinements to make them even more powerful.
You can assign the selected faces to a Selection Set in the Geometry Editor. That Selection Set will be saved with the scene. When you reopen the scene later, use the Geometry Editor to select by Selection Set, choosing your saved set(s) and then hide the selected faces again. That way you can avoid having to figure out what individual faces to select again after reopening the scene.
Or, rather than just hide the selected faces the first time, you can delete them entirely. In older versions of DS you have to hide first and then delete hidden. In the latest version, you can directly delete selected faces. There is no undo for deleted geometry, so be sure. Don't delete geometry if you intend to dForce clothing over that area, or you think you might want to change clothing to something that might expose that area. Deletion of geometry is saved with the scene.
You can add a a Push Modifier Weight Node (on the Create menu) and use the Weight Brush Tool to paint a map of where to add the push. That way, you can be very selective and not push the entire object. You can add multiple push modifiers, each with its own weight map.
These are terrific suggestions! Thanks! I'll have to experiment with them when I get a chance. The Mesh Grabber product might have a lot of potential, especially!
Mesh grabber is really useful and convenient.
Update: In my very first/early test with adding SubD and smoothing to the sheet my character's kneeling on after setting her as the collision item, there is an immense improvement with smoothing and collision each at 20! In practice, though, how high should I need to go with those settings, maximum? Higher seems to be better in this case, though I'm not sure if there's merit in going above 20. Wonders so far, though, in terms of just having the sheet be "displaced" by her shins more naturally! I use smoothing all the time, but never thought of it for this scenario! Thanks for all the brillian suggestions!
Smoothing can be a blessing and a curse. Going too high can really slow down your viewport at times if you are doing a lot of adjustments in the scene. Watch out for that Interactive Update button! That is a viewport speed killer. Sometimes the smoothed item crosses the interference boundary in the wrong direction, like her knee cuts through the sheet instead of pushing it down. Each situation is unique and requires experimentation. 20 sounds reasonably high but not excessive. I wouldn't drag the slider to the max setting! I've never found a benefit from increasing the number of collisions.
I never use interactive update, so no worry there. I do a lot of glamour-oriented portraiture, and have always been plagued by floor sheets intersecting my characters' limbs, hands, etc,. rather than being naturally displaced by them. This may be just the ticket!
Have you ever experimented with dForce on the sheets? If the sheets are reasonably high poly at base resolution, that might work nicely to make natural interactions.
Actually, not yet, because I have had issues in the past with dForce items "falling through" planes and other geometry, but it's worth a try!
dForce only collides with mesh at its base resolution. Adding subd won't make it denser for the purpose of dForce collision. If your sheet is a plane with no or few divisions, if will be useless for dForce collision. A sheet is just a plane, more or less. You could create a primitive plane of any density you want, apply a shader and call it a sheet. You could create another dense plane for the collision floor. You can place that on top of your "real" floor and set the "fake" dense floor's visibility to Visible in Render OFF. Have you followed the dForce thread? It is incredibly inspirational and educational. It is full of helpful tips.
Edit: actually I might be wrong about that detail. I think the thing you are dForcing only uses base resolution for calculation of collision, but the thing you are colliding with might use SubD.
Whenever I buy clothing I seem to end up spending time in Blender using scuplt mode to fix poke through. Since dForce was introduced it has helped somewhat but I still need to get the basic fit right - especially for some of my unorthodox characters (morphed). Unlike many here, I found Mesh Grabber to be less convenient than exporting/importing morphs. At least I can save the morphs and I find the sculpt tools in Blender much more user friendly than the vertex pushing gizmo in Mesh Grabber. But each to her/his own.
What we really need, of course, is for dForce to include that feature that VWD and Marvelous Designer have - the ability to move the mesh while it is draping. You can just tug the cloth to fit over the difficult areas.
Another tip if you want to dForce a sheet with a floor and a person, is to use an animated simulation and start with the sheet above the floor and the person above the sheet. Let the sheet fall to the floor and lower the person onto it. (Don't apply dForce to the person!) You don't want anything colliding when you start the simulation.
I'm working on an image set now, and actually, smoothing and sub-D seem to be ironing out the major kinks, but I'm having to re-render some of the previously unsatisfactory images. I'll still have to experiment with dForce for future application if needed. Tons of tips here... thanks! I'm glad I posted about this.
Didn't realize you could use weight maps with push modifier. Nice.
As for deleting geometry, I hesitate since there's no Undo for it (and sometimes it can alter the shape of entire mesh, whereas just hiding faces always leaves mesh shape intact).
I tried the dForcs sheet idea. It works pretty well, but the downside is that you have little control the details of how it drapes onto the floor. You can fiddle with simulation surface parameters and angle and distance the sheet drops, when G8F interacts with it, etc. but then everything is out of your control during actual simulation. It might be interesting to try it in Marvelous Designer. I added subD to get nicer draped curves on the sheet but didn't need any smoothing between the sheet and G8F.
Wow! Worth trying! Thanks for this effort!
The sheet example confused me. You Sim the sheet to the floor then manually (I assume) lower the figure on top of it.
Did you re-start the Sim at this point? Is it even possible to re-start a sim (I thought it always re-ran from scratch). If you didn't re-start the sim, how did you get the sheet to conform to the person (e.g,. the sheet curving around the right hand in your image is more than mere smoothing).
The sheet is positioned above the floor and the posed G8F is positioned above the sheet. I used an animated simulation to drop the sheet and the character to the floor at the same time in the same simulation. When I get home,I'll attach an illustration.
Ohhh, the animation itself dropped the figure! Duh. Thanks for explaining!
Smoothing and Sub-D really work a treat, with some limitations, for instance, only being allowed one collision item per surface. I suppose there's no remedy for that?
Not really.
Sometimes tho, I'll just render twice, once with each collision item, then merge in post.
I suppose that might work in some instances. It's worth keeping in the bag of tricks.