Added "fake inputs" for pressure and barrel rotation. Now you can make on-the-fly expressive adjustments to your brush even while using a mouse! Change pressure with alt+shift+(a,s) and change the "twist" with alt+shift+(d,f).
To try the barrel rotation, please try out this special brush pack to see how it works. If you have a fancy stylus like a Wacom Art Pen that supports real barrel rotation only Linux seems to have this support from the GTK libraries at the moment. Look for new preferences (in settings.json) that affect barrel rotation offsets and to disable it if necessary.
Merging layers is improved, but some work to do still for groups. If your merge a pigment layer down the result will remain as a pigment layer instead of switching to Normal additive, and vice versa.
Spectral Paint/Pigment layer and brush mode
Linear blending for non-pigment layers and brush modes
Smudge enhancements
Layer "views"
Fullscreen improvements
Python3 compatibility
Art Pen/ Barrel rotation input
Fake inputs for pressure and Barrel Rotation- use your keyboard!
A bunch of other stuff!
Please note, old files will composite layers in a linear "more physically correct" way. This might look different, better, or perhaps worse. We could add legacy modes but it is probably better to move on if possible, or render old files with an older version of MyPaint if necessary (or even Gimp/Krita).
The pigment mode is default for all brushes and new layers. If for some reason you don't like it, or it is too slow, you can slide the "Pigment" slider to off (from the tool options panel), and change the layer mode to Normal. This will go back to a linear RGB blend mode (but not non-linear like the old MyPaint).
Highly recommend my brush pack ("Dieterle", included in AppImage and Windows) to see many new features in action.
special thanks to @aferrero2707 for the appimage build setup