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Distortion under arms

Hey everyone, I've been making assets for a mobile game but the style of clothes is relatively realistic. So what happens a lot is I'll bake from a high res onto the low and it looks fine in the baked pose. Then when I get to rigging/skinning I run into this issue where the stretched polys accentuate the waviness.

It gets baked in an A-pose but then forced into a T-pose for the engine. I understand waviness is a symptom of the game res mesh not faithfully matching the curvature of the seam under the arm - but I'm wondering if anyone else encounters this on the reg and what they do to mitigate it?

The polycount needs to be kept low so what I've been doing is cutting in geo just in this one area (and other areas like the crotch for pants) and then collapsing down the shoulder. Other than that though, are there improvements I can make? Design wise? Baking in a different pose? A mid-poly bake; I've tried this before but when the game-res has triangles (which it often does), these areas look much rougher.

I often look through other game models to study (I'm internet-taught) and I see the loops don't always match the curvature but when stretched, the problem doesn't seem as bad as on my models. Sometimes I'll have edgeloops go up to 22 whereas I've seen others have made 14/16 work. Perhaps the skinning is also to blame?

The below example is just something I quickly threw together to illustrate the issue. It doesn't look that bad here but some of the items for the game are much worse. I'd appreciate any input or tips on where I can improve. Thanks a lot!



Replies

  • pior
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    pior grand marshal polycounter

    The wavyness is not really caused by the high having more definition, but by the angle at which the rays are cast. A highres cylinder can be baked down perfectly cleanly to a 6-sided lowpoly as long as the rays are cast perfectly perpendicularly to the surface of the low, and catching the high as intended.

    You have the anser right there : making the stitch match the red seam perfectly, either by controlling the ray direction (plenty ways to do that : by splitting the meshes, and/or using a cage, and/or painting skew control in Toolbag...), or by doing some good old manual cleanup of the textures.

  • Retticle


    Thanks for your reply, appreciate you taking the time to read through my post.

    Would you mind elaborating on your suggestion of splitting the meshes? I tried painting skew quickly in Marmoset and while it did help somewhat, I found it difficult to control and ended up with a double seam. Maybe because the shift in angle is so great under the arm?

    Yeah, I guess manual cleanup is always an option - albeit one I was trying to avoid haha.

  • Kanni3d
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    Kanni3d ngon master

    Skew painting produces a (natural) artifact when painting along UV borders. I'd only paint skewing in that areas if the entire thing was a contiguous UV shell (which still would have a seam running along it laterally).


    You can temporarily split the mesh upon the highpoly seam/uv seam, then merge them together post-bake. Could also try baking with twice the amount of cylindrical segments for more ray casts, and then removing them post bake. Shading wouldn't be 100% identical so there may be a gradient artifact, but that may resolve the initial problem somewhat.

  • pior
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    pior grand marshal polycounter

    Well, splitting in and off itself woudn't solve the issue but it would give you some wiggle room - like the ability to finely control the ray direction on both sides of the seam, moving pieces apart to completely prevent any influence of one side over the other, and so on. At this point it is not so much about the tech itself and more about ways to force it to do what you want.

    Also it's important to keep in mind that even though the shading information comes from a highpoly sculpt that probably took hours, it being baked down to a normalmap accounts for (quite litterally) the most minor and tertiary surface information of the whole thing. Therefore and especially on such low-end models there should be no fear to break the rules so to speak, like with some manual cleanup or any other trickery.

    I'd suggest exploring other forms post-processing too - like for instance making sure that UV seams match garment seams so that they can then easily be detected in PS and have some global procedural bevel effect applied to them. It opens up a lot of possibilities, especially with very lowres textures.


  • Retticle

    @Kanni3d Oh I see, yeah definitely not contiguous as I usually try my best to cut a seam along the natural garment seams. I have experimented with using mid-poly bakes by subdividing w/ no smoothing on the uvs and it does help - but tends to mess up any parts of the mesh that contain triangles. I guess a solution could be to blend between two maps - a midpoly bake for areas like this and a regular bake for everywhere else.


    @pior Thanks for clearing that up. And yeah I find it difficult 'breaking the rules' mostly because I don't want anyone who has to make modifications after to have to suffer as I have - but I definitely see your point. And yes! I have been thinking perhaps it's best to leave out garment seams in the high poly all together esp in high stretch areas like this and just do them in post. Thanks to you both for all your help.

  • Kanni3d
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    Kanni3d ngon master

    Yeah adding UV seams upon natural garment seams is the way to go (especially helps skewing),

    You can just add the loops manually to make the cylinder twice as round, so it doesn't sub-divide the rest of your model where it isn't needed or necessary. Blending the two maps is just a destructive and cumbersome.

  • Retticle

    @Kanni3d Oh smart! I never thought of that. Thanks for the tip.

  • Retticle

    One other question I'll throw out there; I usually only notice stuff like this once the mesh has been skinned and placed in a different pose (as it looks fine at all angles in the bake pose). Is it common practice to do skinning tests as you texture to catch this stuff ahead of time - or are others just more vigilant/careful?

  • Kanni3d
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    Kanni3d ngon master

    Best to do this stage at the most neutral/relaxed state. T pose is not a natural/relaxed state which is largely why A-pose has been adopted.

  • Neox
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    Neox veteran polycounter

    What? No!

    The neutral us totally depending on the range of motion. If the character does an awful lot, yes the Tpose is the most neutral you can get.

    If all you character ever does is holding a gun with lowered arms and angled elbows, your neutral can be closer to this. But have fun once your designer decides the character has to throw grenades. You will get the worst stretching ever in the arm pit.

  • oglu
  • Kanni3d
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    Kanni3d ngon master

    Granted im no character artist 😅

    but i've always heard, and even feels like, that a t-pose is an extension/flexion. Everything's at 90 degrees, while A is 45, somewhere in the middle of the extremes. It takes energy/muscle activation to get your arms to that state, A-pose has much more relaxed, "neutral" muscles, wouldn't it?

    edit: but yes, if your character does tons of wild stuff with their arms, t-pose would be in the middle of the extremes

  • pior
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    pior grand marshal polycounter

    • A well made A-pose is great - it's also very, very difficult to get right, and is often the subject of endless discussions during preproduction with some people arguing outside of their actual field of expertise. And then it tends to result in a compromise that can have a negative impact throughout a project. A badly put together A-pose can even negatively affect the perception of the work during review because if it is ever so slightly off-balance the models will just all look weird.

    • A well made T-pose is not only just as great technically, it is also near impossible to screw up as even the most junior modelers will naturally get it right (legs straight down, horizontal arms, fingers perfectly aligned with the direction of the limbs, and so on).

    If anything I feel like the following is pretty good : the arms are at a strict 45 degrees, and everything else is just as straight as it can be. No so-called "relaxed" stance of the spine or fingers or anything of the sort. It's may seem a bit stiff of course, but it is very straightforward and gets things done.

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