Joystick support

[maximilien-noal]

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[maximilien-noal]

See #222

[maximilien-noal]

I now know why I could not implement Gamepad support for Dune / generic Joystick support.

DOSBox IO dispatcher class runs the emulation loop and passes I/O port read writes through AL (and takes care of saving/restoring it). In the emulation loop, if the PIC runs its queue (meaning it had hardware interrupts pending), the emulation loop returns.

We don't do that. Thing is, I really want to avoid to do that!

But this is also how the keyboard controller works. The IRQ1 hardware interrupt handler (INTH 09) is supposed to get/read data through keyboard ports (and therefore via CPU register AL) and be interruptable by programs which can inspect AL.

See INT 15 C - KEYBOARD - KEYBOARD INTERCEPT in the RBIL.

[maximilien-noal]

Dune joystick support can be done now, especially when one compares the current architecture and input logic and emulation loop and emulation loop scheduler vs dosbox staging.

Only missing pieces:

A faithful port of the relevant parts of SDL2 ( https://github.com/libsdl-org/SDL see SDL2 branch) to C# for all platforms (Windows desktop, Linux desktop, mac deskttop)

A faithful emulation part from dosbox staging

A Joystick UI will have to be provided, with feedback. Both for feedback when using a modern XInput controller on the host, and as AvaloniaUI level keyboard driven emulation of a joystick when one does not have an actual controller.

Considerations:

Emulation of the soundblaster gameport will have to be complete and faithful.
Take into account the relevant sections for configuration of the emulated hardware (see dosbox conf file)
We don't care about remapping and the dosbox mapper layer. This is a mess we don't want to import.