incorrect undo of roll specific model

[Elaine Meng]

The attached session square-assembly.cxs has two models #2.1 and #2.2 making up a square assembly. The session restore position is a view named "middle". Session made/tested in UCSF ChimeraX version: 0.92 (2020-02-20)

All of the following commands undo perfectly, as can be assessed by executing them, and then "undo", and then "view middle" (which should not cause any change).

turn y 90
roll y 90 1
turn y 90 models #2.1

However, this one does not undo back to the previous position:

roll y 90 1 models #2.1

After the "undo" the square is not square, and "view middle" changes noticeably to get you back to the square.

Maybe the difference is not roll vs. turn but the inclusion of a frame argument?

[Conrad Huang]

Fixed in 49f498967.

Make multi-frame turns use the same cofr instead of recomputing each frame, which causes the rotation to precess if only some models/atoms are rotated.