The main advantage of this change is that heavy-weight filters do not
lock up the GUI anymore.
This first cut has several flaws:
- We do not account for modification of the referenced images while the
filter is running. Depending on the exact filter behavior this might
have all sorts of weird effects. A simple fix would be to show a
progress dialog to the user, preventing them from performing other
modifications in the meantime.
- We do not use the image processor for previews. Preview behavior has a
couple of other considerations that are intentionally not addressed in
this commit or pull request.
The ImageProcessor singleton is intended to be used by all sorts of
image processing which might take some time to complete; or other
background actions. We're not using BackgroundTask here because this
system is specifically designed to work with task queues and PixelPaint
interaction; e.g. it provides common image processing tasks such as
filter application.
