Allow selecting through holes in mesh surface

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Begin forwarded message:

From: Tristan Croll
Subject: Suggestion: split mouse selection mode into "atoms", "maps" or "all"
Date: December 6, 2016 at 4:29:10 AM PST
To: Tom Goddard

Hi Tom,

This is a suggestion I've been meaning to bring up for a while. The way mouse picking works at the moment (get the first object under the pointer for ctrl-click, or everything under the rectangle for ctrl-click-and-drag) becomes quite problematic when working with atom-map combinations, I find. For example, when trying to select an atom in an ISOLDE sim to do something with in the menu, if the atom is inside the map contour then the only way I can select it is by ctrl-click-and-drag (which risks bringing in background atoms for the ride) or first hiding the map. I know most (all?) crystallographers are used to the map being essentially a constant field rather than a tangible object that can be selected and moved, so only atoms will interact with the mouse. Conversely, in situations where you *do* want to select map(s) or fragments thereof, I imagine it's most common to only really want to work on the maps and not the atoms. I can of course easily set up a custom mouse mode to work that way in ISOLDE, but I think it would make a lot of sense to provide the choice of selection modes in ChimeraX itself.

Cheers,

Tristan

[Tom Ferrin]

See #503.