`GdkPaintable` is a simple interface used by GTK to represent content that can be painted.
The content of a `GdkPaintable` can be painted anywhere at any size without requiring any sort of layout. The interface is inspired by
similar concepts elsewhere, such as
ClutterContent, [HTML/CSS Paint Sources](https://www.w3.org/TR/css-images-4/paint-source), or
SVG Paint Servers.
A `GdkPaintable` can be snapshot at any time and size using [[email protected]]. How the paintable interprets that size and if it scales or centers itself into the given rectangle is implementation defined, though if you are implementing a `GdkPaintable` and don't know what to do, it is suggested that you scale your paintable ignoring any potential aspect ratio.
The contents that a `GdkPaintable` produces may depend on the [class@GdkSnapshot] passed to it. For example, paintables may decide to use more detailed images on higher resolution screens or when OpenGL is available. A `GdkPaintable` will however always produce the same output for the same snapshot.
A `GdkPaintable` may change its contents, meaning that it will now produce a different output with the same snapshot. Once that happens,
it will call [[email protected]_contents] which will emit the [signal@GdkPaintable:GdkPaintable:invalidate-contents
s] signal. If a paintable is known to never change its contents, it will set the
gdk_paintable_static_contents flag. If a consumer cannot deal with changing contents, it may call [
[email protected]_current_image] which will return a static paintable and use that.
A paintable can report an intrinsic (or preferred) size or aspect ratio it wishes to be rendered at, though it doesn't have to. Consumers
of the interface can use this information to layout thepaintable appropriately. Just like the contents, the size of a paintable can
change. A paintable will indicate this by calling [[email protected]_size] which will emit the [signal@GdkPaintable:
GdkPaintable:invalidate-size] signal. And just like for contents, if a paintable is known to never change its size, it will set
the gdk_paintable_static_size flag.
Besides API for applications, there are some functions that are only useful for implementing subclasses and should not be used by applications: [[email protected]_contents], [[email protected]_size], [[email protected]_empty].