Why Video Game Breasts Physics Can Go Wrong
“Mechanically, breasts anchor off the pectoral but loop up and connect at the shoulder, so they get pulled back when the clavicles move,” Tim Dawson, an indie developer that has previously worked on games like LA Noire, told me.
Once breasts are rigged, developers can add breast physics in a couple of ways. Breast movement might be dictated by a simulation system that lets developers add “springs” to breasts. These springs take motion and use it to determine how much something should move after, say, a character jumps up and down.
Springs help make it so that breasts can continue to move even after a character becomes still. If a character has two springs, one might be used to determine how far a breast bone is distanced from the sternum, and a second spring might control how much the breast deviates from its starting point. Then, on top of all of that, developers can add a dampening effect that determines how long it takes for the breasts to settle down.
“Imagine the character standing up,” Dawson said. “The sudden movement would pitch the breast bones downwards. Then when the character reaches their standing height, the bones catch up, pitching upwards slightly, then back down and come to a rest. This would be a procedural breast bounce and settle. The rest just comes from thinking it through: how much heft are [the breasts] likely to have, how well-supported are they?”