* Adds Window Manager support to the Supervisor, so that Window widgets
can be dragged by their title bar, clicked to focus, etc.
* Create a ui.Window as normal, but instead of Packing or Placing it
into a parent container as before, you call .Supervise() and give it
your Supervisor. The window registers itself to be managed and drawn
by the Supervisor itself.
* Supervisor manages the focused window order using a doubly linked
list. When a window takes focus it moves to the top of the list.
Widgets in the active window take event priority.
* Extended DragDrop API to support holding a widget pointer in the drag
operation.
* Changed widget event Handle functions to return an error: so that they
could return ErrStopPropagation to prevent events going to more
widgets once handled (for important events).
Some bugs remain around overlapping windows and event propagation.
* Tooltip can be added to any target widget (e.g. Button) and pop up on
mouse over.
* Refactor the event system. Instead of passing a render.Point to all
event handlers, pass an EventData struct which can hold the Point or
the render.Engine.
* Add event types Computed and Present, so a widget can set a handler on
whenever its Computed or Present method is called.
* Button: do not call MoveTo inside of Compute().
* Label: do not call MoveTo inside of Compute().
* MainWindow: add OnLoop callback function support so you can run custom code
each loop and react to the event.State before the UI updates.
* Supervisor: locate widgets using AbsolutePosition() instead of w.Point()
to play nice with Frame and Window packed widgets.
* Widget interface: rename Adopt() to SetParent() which makes more sense for
what the function actually does.
* Window: set itself as the parent of the body Frame so that the Supervisor
can locate widgets anywhere inside a window's frames.
Frame packing fixes:
* Widgets with Expand:true grow their space with ResizeAuto to preserve the
FixedSize() boolean, instead of being hard-resized to fill the Frame.
* Widgets that Fill their space are resized with ResizeAuto too.
Outstanding bugs:
* Labels don't expand (window title bars, etc.)
* Initial WebAssembly build target for Doodle in the wasm/ folder.
* Add a new render.Engine implementation, lib/render/canvas that uses
the HTML 5 Canvas API instead of SDL2 for the WebAssembly target.
* Ported the basic DrawLine(), DrawBox() etc. functions from SDL2 to
Canvas context2d API.
* Fonts are handled with CSS embedded fonts named after the font
filename and defined in wasm/index.html
* `make wasm` builds the WASM program, and `make wasm-serve` runs a dev
Go server that hosts the WASM file for development. The server also
watches the dev tree for *.go files and rebuilds the WASM binary
automatically on change.
* This build "basically" runs the game. UI and fonts all work and mouse
movements and clicks are detected. No wallpaper support yet or texture
caching (which will crash the game as soon as you click and draw a
pixel in your map!)
* MainWindow is ideal for apps that just want a UI and
don't manage their own SDL windows.
* The example app will grow into a series of demos that
test the UI toolkit to help fix bugs and grow features.
