I tested a few more programs from the
EnterMice wiki:
CM2000,
PASZIANS.COM,
SPEmu128 - these work fine in ep128emu with mouse input
PaintBox - works after loading MOUSE.XR and setting EnterMice mode with SET 189,4
SWAP - moving the pointer works, but the button does not because the game tests the state of the EXT1 fire buttons outside the 1500 us time the emulator allows for mouse I/O after the RTS bit changes. Pressing the actual EXT1 fire button does work, however
SymbOS - does not work, it expects mouse input on column J, which is not supported by ep128emu. Perhaps it can be configured somehow to use native EnterMice mode?
EGI - works after replacing the :VAR 189 0 with :VAR 189 4 in EXDOS.INI
EDC Windows - it works, but because of the low horizontal sensitivity, the pointer will frequently hit the left/right edges of the emulator screen
While FLTK does not support mouse grabbing and relative motion, I may try using native APIs (XWarpPointer() on Linux and SetCursorPos() on Windows) in the "fullscreen with no menu bar" mode to center the pointer whenever it gets too close to the edges.