Add support for built-in property aliases and rename `color` to
`background` - in preparation for it also changing to type brush.
Right now the alias is silent, a deprecation and overall change
will come in a subsequent change.
This intends to provide a configurable rectangular "drop shadow". The
API is modeled after CSS/HTML5 Canvas where the element can be "bound"
to an existing rectangular shape (geometry and radius), the offset can
be used to place the shadow and color and blur configure the shadow.
The shadow's color fades into transparent.
TODO (in subsequent changes):
* Documentation
* Qt implementation
Fold CharacterInput into KeyPressed/KeyReleased and store the "key" as a string.
Also, instead of exposing the KeyCode we're encoding special characters
into the string.
For all other items the default is the empty size.
This also required three fixes for the HTML image loading:
* The upload_pending property value was inverted, it needs to start
out as true (pending yes) and be set to false when it finished
loading (not pending anymore)
* Mark the upload_pending property as dirty before scheduling the
redraw, in case it's sync
* Pass the item rendering cache to the image_size function to ensure
that the Rc<CachedImage> is not only weak inside the image_cache
of the GLRendererData but also strong on the item.
This means going back to an immutable renderer reference and interior
mutability for the canvas and the gpu cache. This is because while
traversing the item tree for rendering we may end up destroying
other items due to the lazyness of the models.
This is the start of a different rendering abstraction, the result of a
separate discussion.
The objective is to provide a better backend encapsulation, that will
make it easier to implement other backends and let the backend decide
what to cache and what not. This is done by passing the struct with the
Property<> fields directly to the backend, so that it can decide what
the cache and what to use every time.
This allows implementing another sliding puzzle theme feature, the
boldness of the tile number text in the simple theme when the tile is in
the correct position. For the other themes the weight is constant and
it's bold.
More cleanup to follow later: unify the font handle and FontCacheKey
handling, improve the API to allow for the use of symbolic constants
(normal, bold, etc.) instead of the CSS number values.
Group all fields we need to determine a physical font into one FontRequest
structure and use that throughout.
That way adding more fields will require less changes.
To make adding of more font related properties easier in the future, and
to simplify the text code a little, define a HasFont trait and implement
it for Pin<&Text|&TextInput> so that we can more easily get an Rc<Font>.
