Synchronized scrolling of multiple tree views

[westram]

Applies only if multiple views are visible/shown.

Each view should be assignable to a master-view. Doing so will make the view a slave-view.

Master-views do

• collect a list of all species displayed inside viewport (during refresh of canvas)
• flag collected species
• trigger a sync-jump in all associated slave-views (only if list of visible species did change)

Slave-views can perform a sync-jump:

1. draw (onto size device?) and collect positions of flagged species
2. find part of containing most flagged species
   1. search in Y-range for dendro- and IRS-view
   2. also change zoom for radial- and circular-view
3. scroll there (explicit scrolling needs to be delayed until all slave-views of the currently triggering master-view performed their sync-jump; otherwise flags would be overridden)

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Notes:

• a master may also be a slave (deny looped chaining)
• a master may have multiple slaves (but not vv.)
• during a sync-jump one of the unused ​DB-flags may be used to flag which species are visible in master-view
• code triggered by the JUMP button might be related

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Umbrella ticket: #444

[westram]

by [15340]

still TODO adjust zoom for radial view