While ideally this should be implemented by the OS and tablet
driver, some applications implement their own tablet pressure
curve support. This allows tweaking based on task, and work-
arounds for missing OS-level options.
A full custom curve like in Krita is probably overkill for
Blender, so this adds two simple options:
- Pressure required to achieve full brush intensity.
- Softness control, using a gamma curve internally.
The important one is the max pressure setting, because it is
critical for ergonomics, but the Linux Wacom driver lacks it.