"Smooth" cursor scrolling #2371
Description
As proposed here: #2046 (comment)
Current Behavior:
AlphaTab supports two scrolling modes: Continuous and OffScreen. Meaning it only scrolls abrupt when the respective condition applies (out of screen, or "next bar/system").
New Behavior:
It would be nice if alphaTab can scroll more continuously. As the song is playing, bringing a smooth experience to the UI.
For horizontal layouts we would change the "animate cursor" to an "animate music sheet" scrolling. The cursor would stay rather fixed and the music sheet scrolls. The cursor placement might need to be configurable (left, center, maybe a percentual x-offset).
For vertical layouts we could estimate how long the cursor will last within the current system (row) and do a slow-but-steady scrolling upwards so that the next system is again centered/top-aligned when we would normally scroll rapidly at the end. Obviously the currently played system should never become invisible while still playing. Again we might want to choose whether the "current scroll" is top-aligned, centered or a custom percentual y-offset. To ensure the current system is always visible we might need to do a special calculation and still do a "fast" scroll at the end to avoid the system scrolling out-of-viewport.