Add the ability to drag and drop Doodads onto the level. The Doodad
buttons on the palette now trigger a Drag/Drop behavior when clicked,
and a "blueprint colored" version of the Doodad follows your cursor,
centered on it.
Actors are assigned a random UUID ID when they are placed into a level.
The Canvas gained a MaskColor property that forces all pixels in the
drawing to render as the same color. This is a visual-only effect, and
is used when dragging Doodads in so they render as "blueprints" instead
of their actual colors until they are dropped.
Fix the chunk bitmap cache system so it saves in the $XDG_CACHE_FOLDER
instead of /tmp and has better names. They go into
`~/.config/doodle/chunks/` and have UUID file names -- but they
disappear quickly! As soon as they are cached into SDL2 they are removed
from disk.
Other changes:
- UI: Add Hovering() method that returns the widgets that are beneath
a point (your cursor) and those that are not, for easy querying
for event propagation.
- UI: Add ability to return an ErrStopPropagation to tell the master
Scene (outside the UI) not to continue sending events to other
parts of the code, so that you don't draw pixels during a drag
event.
Adds the first features to Edit Mode to support creation of Doodad
files! The "New Doodad" button pops up a prompt for a Doodad size
(default 100px) and configures the Canvas widget and makes a Doodad
struct instead of a Level to manage.
* Move the custom Canvas widget from `level.Canvas` to `uix.Canvas`
(the uix package is for our custom UI widgets now)
* Rename the `doodads.Doodad` interface (for runtime instances of
Doodads) to `doodads.Actor` and make `doodads.Doodad` describe the
file format and JSON schema instead.
* Rename the `EditLevel()` method to `EditDrawing()` and it inspects the
file extension to know whether to launch the Edit Mode for a Level or
for a Doodad drawing.
* Doodads can be edited by using the `-edit` CLI flag or using the
in-game file open features (including `edit` command of dev console).
* Add a `Scrollable` boolean to uix.Canvas to restrict the keyboard
being able to scroll the level, for editing Doodads which have a fixed
size.
