* Add initial Ellipse Tool to the Editor Mode. Currently there's
something wrong with the algorithm and the ellipses have a sort of
'lemon shape' to them.
* Refactor the IterLine/IterLine2 functions to be more consistent.
IterLine used to be the raw algorithm that took a bunch of coordinate
numbers and IterLine2 took two render.Point's and was the main one
used throughout the app. Now, IterLine takes the two Points and the
raw algorithm function removed.
* Implement Brush Sizes for drawtool.Stroke and add a UI to the tools panel
to control the brush size.
* Brush sizes: 1, 2, 4, 8, 16, 24, 32, 48, 64
* Add the Eraser Tool to editor mode. It uses a default brush size of 16
and a max size of 32 due to some performance issues.
* The Undo/Redo system now remembers the original color of pixels when
you change them, so that Undo will set them back how they were instead
of deleting the pixel entirely. Due to performance issues, this only
happens when your Brush Size is 0 (drawing single-pixel shapes).
* UI: Add an IntVariable option to ui.Label to bind showing the value of
an int reference.
Aforementioned performance issues:
* When we try to remember whole rects of pixels for drawing thick
shapes, it requires a ton of scanning for each step of the shape. Even
de-duplicating pixel checks, tons of extra reads are constantly
checked.
* The Eraser is the only tool that absolutely needs to be able to
remember wiped pixels AND have large brush sizes. The performance
sucks and lags a bit if you erase a lot all at once, but it's a
trade-off for now.
* So pixels aren't remembered when drawing lines in your level with
thick brushes, so the Undo action will simply delete your pixels and not
reset them. Only the Eraser can bring back pixels.
* Add new pkg/drawtool with utilities to abstract away drawing actions
into Strokes and track undo/redo History for them.
* The freehand Pencil tool in EditorMode has been refactored to create a
Stroke of Shape=Freehand and queue up its world pixels there instead
of directly modifying the level chunker in real time. When the mouse
button is released, the freehand Stroke is committed to the level
chunker and added to the UndoHistory.
* UndoHistory is (temporarily) stored with the level.Level so it can
survive trips to PlayScene and back, but is not stored as JSON on
disk.
* Ctrl-Z and Ctrl-Y in EditorMode for undo and redo, respectively.
