While there is a style "background color", the idea of a "widget
background color" is completely bogus, the widget background can be a
gradient or whatever.
- Get rid of "background" in GimpViewable's preview API, only leave the
"foreground color" there for things like brushes or fonts.
- In GimpViewRenderer, add the background types to be used to class and
instance, so each renderer type can choose what it needs.
- Render all previews to alpha surfaces, and do the background
for all renderers generically in gimp_view_renderer_real_draw(),
then render the preview surface on top of it.
This also depends on the same settings to render brushes with theme
colors, because this is data, not user interface. Therefore following
theme colors is not necessarily what creators would expect.
Previous code was using the correct background color from the theme, but
the foreground color was always either white or black (depending on GUI
config color scheme). Instead, just use the foreground color from theme.
Since core/ doesn't have access to GTK, hence the theme, we had to
update GimpViewable's get_preview() and get_pixbuf() abstract methods to
have a color argument for recoloring previews (when relevant, which for
most types of viewables is not).
We don't try anymore to convert early from a pickable color to another
format/space. Now we are able to get a GeglColor and move it around,
doing only last-second (when needed) conversions.
Replaces GimpPickableInterface's pixel_to_srgb () functions with
pixel_to_rgb(). Now GimpRGB's values should be in the correct
image color space from the beginning of the process.
In GimpImageProxy, implement GimpColorManaged by forwarding the
functions to the underlying GimpImage, and forwarding the signals
in the other direction. This fixes color-managed view in the
Navigation dockable.
In GimpImageProxy, implement the GimpPickable interface, so that
the proxy can be used as both a viewable and a pickable for the
image projection, with direct control over the show-all mode. This
will allow us to use a GimpImageProxy as input for a GimpLineArt.
