camera-fit

Where a chase camera is allowed to be. Pure — distances and heights, no Babylon, no rays — so the rules can be tested without a scene.

Two problems that look unrelated and are the same problem:

• A wall between you and the camera. The camera sits behind the character; the character backs into a corner; now you are looking at the inside of a wall, or through it at nothing.
• The camera at a medium boundary. Half the frame should be underwater and is not, because fog is one value per frame (MEDIUM-DESIGN §6a).

Both are the camera is somewhere it should not be, and both are fixed by moving it — pull it in, or push it out of the band. Tonio, joining them up: "The same sort of correction could handle the medium boundary issue." So this module is a list of corrections applied to a desired position, rather than two features that each own a camera.

Snap IN, ease OUT — and that asymmetry is the whole feel

A wall arrives between you and the camera in one frame, and you must be inside it that frame: easing in means one or two frames of looking through geometry, which is the artifact every third-person camera is judged on.

Coming back out is the opposite. The ray that found the wall will flicker at its edge — a pillar, a doorway, a railing — and easing out is what stops the camera pumping in and out at 60Hz while you stand still. Different rates for the two directions is not a polish detail; it is the difference between a camera that works and one that makes people ill.

The band case IS the Manta flip

MEDIUM-DESIGN §6a records how Manta solved the waterline on an iPhone 3G: flip the camera from decidedly above to decidedly below, so the state never arises. Expressed here, that is one more constraint — stay out of this band — and it composes with the wall correction instead of being a second mode with its own camera code.

Which side it goes to is decided by the subject, not by the camera: if the swimmer is under, the camera goes under. A camera that picked the nearer side would cross the surface every time the character bobbed.