DepthOfFieldSettings class final

Depth of field, from a lens rather than from a ramp — gfx-34n.

Every number here is one a photographer already knows. A focus distance, a focal length and an f-number are what a lens is described by, and the circle of confusion that follows from them is the thin-lens formula rather than a curve chosen because it looked right. Open aperture and the background softens by an amount somebody can predict from the three numbers, which a strength slider between zero and one cannot offer.

The depth comes from the surface buffer's alpha, which carries distance along the view axis in metres. That is the same channel the shafts read, and the reason the engine keeps it rather than depending on a sampleable depth attachment: the formula wants a real distance, and a window depth would make the same blur mean different things near and far.

Off by default, with defaults that are a no-op if it is switched on blind — focusDistance is far enough and aperture narrow enough that nothing in an ordinary scene leaves focus until somebody says so.