volume from silhouette

The third model decision is made and the volume feature is real. The engine now carries a third pinned model, a segmentation pass, plus a working body sculpt: feed it a reference shape and the character’s hip, waist, chest, and thigh widths move to match it, skeleton provably untouched.

Getting there meant benchmarking five real candidate models on real hardware, checksums, speed, and accuracy each, rejecting six other families with the evidence written down. Funniest catch: the model built specifically for segmenting people was completely blind to the test case, zero accuracy, while the general-purpose model saw it fine and ran cheaper too. The mechanism authors real shape keys per body region, so the adjustable sliders are the solved math directly, and every pose/animation path downstream sees a completely unchanged skeleton.

The real fight was realizing the first passing test was a lie. A whole-frame comparison technically passed on a completely unsculpted body, since the measurement was too insensitive to tell a correctly sculpted shape from an untouched one. Fixed by scoping comparisons to the actual body regions with no model in the loop, publishing a baseline next to every result so a cheating pass can’t hide again. Smaller lessons banked too: a slider silently defaulting to zero killed half its usable range, one rig type needed its math in a different coordinate space entirely or it silently did nothing, leftover scene state poisoned later measurements, and naive bone-weight assignment broke the hip region specifically.

Numbers came out solid: worst-case regional accuracy clears the bar across every test case, width delivery lands exact to four decimal places, solved values track intended targets within about 3% through the real model, and resetting a sculpt restores the original mesh almost exactly.

Next: wire both sculpts into the real user-facing flow, and prove the sculpt survives animation, set once, then animate, and the widths hold.