.. and simplify the implmentation of displayio_area_union
This _slightly_ changes the behavior of displayio_area_union:
Formerly, if one of the areas was empty, its coordinates were still
used in the min/max calculations.
Now, if one of the areas is empty, the result gets the other area's coords
In particular, taking the union of the empty area with coords (0,0,0,0)
with the non-empty area (x1,y1,x2,y2) would give the area (0,0,x2,y2)
before, and (x1,y1,x2,y2) after the change.
Different operations to the display tree have different costs. Be
aware of these costs when optimizing your code.
* Changing tiles indices in a TileGrid will update an area
covering them all.
* Changing a palette will refresh every object that references it.
* Moving a TileGrid will update both where it was and where it moved to.
* Adding something to a Group will refresh each individual area it
covers.
* Removing things from a Group will refresh one area that covers all
previous locations. (Not separate areas like add.)
* Setting a new top level Group will refresh the entire display.
Only TileGrid moves are optimized for overlap. All other overlaps
cause sending of duplicate pixels.
This also adds flip_x, flip_y and transpose_xy to TileGrid. They
change the direction of the pixels but not the location.
Fixes#1169. Fixes#1705. Fixes#1923.
This changes the displayio pixel computation from per-pixel to
per-area. This is precursor work to updating portions of the screen
(#1169). It should provide mild speedups because bounds checks are
done once per area rather than once per pixel. Filling by area also
allows TileGrid to maintain a row-associative fill pattern even when
the display's refresh is orthogonal to it.
Kevin Matocha
Jeff Epler
microDev
Dan Halbert
Scott Shawcroft