Nothing on this scope is drawn where it stands; every point is where the constraints leave it.
Made of
The sack is a closed ring of 29 points with two corner points on springs, held by distance constraints (edges that bunch but do not stretch, minimum-distance struts across the body), a fold limit at every vertex, one AREA constraint and a depth-weighted pressure that makes the flour pool at the bottom. The tower is 48 blocks welded into a frustum on a hinge, the knife is one line on a cutting path, the penny is one point, and tower, falling blocks, grains, pile and the sack's area target are one ledger of flour that sums to a constant.
Moved by
A relaxation solver runs 6 substeps per frame, warm-started from the previous frame, projecting the constraints until the largest residual is under 2×10-4 or 24 iterations pass; floor contact sticks unless dragged past a threshold, and contact with the tower is shared between sack and tower (tower weight 0.22) and may only cancel the lean the tower is adding, so the cloth stops the tipping but cannot right it. The sack is never placed: its inputs are two light-pen goals (seam centroid, and a base held level) and the corner-spring angle, keyed in time up to 24.5 s; during the gather the seam goal's height and x are computed from the fill fraction (flour taken in over flour still to take), not keyed. The knife's path, the tower's lean drive and the order in which welds are deleted are the authored world; at the fourth cut every weld goes and the penny falls from rest under gravity with air drag (terminal speed 0.20 m/s) until it touches the seam.