Editor: in a View editor, support multiple frame selection

[ivan-mogilko]

This is a repeating user request from old times until today: let select multiple frames in a View editor, which would allow to set property values for all of them at once. Usually people want to set same delay or same Flipped value for a loop, or multiple loops at once.

Properties grid already supports editing multiple objects at once, you may see how this is done for Sprites.

So the main problem here, it seems, to add multiple frame selection.

My proposal is to add classic controls, where:

• Ctrl+Click would select another individual frame,
• Shift+Click would select all frames between last selected one and clicked. I suppose that this should select even multiple loops: e.g. if user selected a frame 0 in loop 0, then Shift+Clicks on a frame 10 in loop 10, then all the frames in all the loops in the middle will also get selected.

UPD
About the code, the View preview pane (ViewEditor class) is constructed of multiple Loop preview panes (ViewLoopEditor class), each controlling its loop. Selection handling is shared between the Loop preview class and View pane class.

EDIT: also, there are methods in ViewLoopEditor working exclusively with "selected frame", instead of accepting a frame as a parameter. This all has to be refactored.

[ivan-mogilko]

I might try doing this, from the first glance this looks like mostly a matter of reorganizing code between two ui classes.