Fixes:
* Various special cases around junctions on pins and dragging.
* Some rotations of endpoints resulting in a 45 degree rotate.
* Some cases where it was possible to get a line with neither
endpoint selected, and also substractive unselecting only one of two
selected endpoints unselecting both.
* Use line midpoint for sorting. Start and endpoints aren't
consistent in the order they appear on the X or Y axis. So,
we need to use the midpoint for our position for consistent
sorting when dragging groups of parallel lines where some
have the start and end reversed.
Other:
* Rename TEMP_SELECTED TO SELECTED_BY_DRAG. This is the actual meaning
of the flag, and should reduce confusion as
to when it should be used.
* Move usage of TEMP_SELECTED as an algorithmic mark to CANDIDATE
instead.
* Fix mistaken clearing of START_POINT and ENDPOINT.
* Move endpoint setting and clearing out of narrowSelection, and into
selectPoint and selectMultiple.
* Don't show dangling end warnings on new lines
In symbols, a polyline descr is already a true polyline / polygon descr.
In schematic, a polyline descr was restricted to only 2 points (a line).
A true polyline / polygon descr is now allowed in schematic that support already
polygons.
For compatibility reason, a 2 points polygon (SCH_SHAPE) is converted to a SCH_LINE.
Also fixes a bug where the auto-start-wire stuff was messing up the seleciton
when the selection tool wasn't at the top of the tool stack.
Fixes https://gitlab.com/kicad/code/kicad/issues/5960
dynamic_cast could not resolve the cast chain leading to a null undo
point. Since we know the item to be LIB_ITEM, we can use static_cast
anyway and avoid the overhead.
Fixes#3771 | https://gitlab.com/kicad/code/kicad/issues/3771
* Ensure the lib edit undo checks for pointer validity
* Assert that the frames are the correct type (satisfies coverity)
* Convert C casts to C++ casts