Enable mouse input via gamepad + various mouse improvements

[jdgleaver]

At present, it is impossible to play mouse enabled games with this core on devices that do not have a physical mouse or touchscreen. This PR adds support for controlling mouse input via a gamepad, with the following new core options:

• Pointer Device:

  • Mouse: Uses physical mouse for input
  • Touchscreen (Pointer API): Uses pointer API
  • Left Analog: Cursor is controlled using the left analog stick of the gamepad in port 1
  • Right Analog: Cursor is controlled using the right analog stick of the gamepad in port 1
  • D-Pad: Cursor is controlled using the d-pad of the gamepad in port 1 (disables normal d-pad input)

• Pointer Speed: Allows the relative speed of cursor movement to be controlled for all input modes other than Touchscreen (Pointer API). Cursor position is determined with sub-pixel precision

• Gamepad Analog Deadzone: Sets the analog stick deadzone (e.g. X360 pads typically need a deadzone of 15% to prevent drift)

Additional gamepad inputs for port 1 are mapped as follows:

• RetroPad R2: Mouse left click
• RetroPad L2: Mouse right click
• RetroPad L: Slows the mouse cursor (for fine control) when using Left Analog, Right Analog or D-Pad for cursor movement

The PR also adds a Mouse Cursor Color option, and fixes 2 mouse-related bugs:

• The mouse cursor can no longer go off screen, or 'wrap around' from one screen edge to another
• There is no longer an erroneous offset between the mouse cursor position and the values registered by games

[RobLoach]

Thanks for the addition, @jdgleaver! Reminds me of ScummVM's emulated mouse pointer. I also really like the use of the enum instead of strings. Nice work!

It looks like this fork is out of sync with libretro:
nesbox/TIC-80@master...libretro:master

Any plans on pushing these changes upstream? There are also changes in TIC-80 that should likely be brought down, like some memory slot fixes. Optimal solution would be to use the original source, but 🤷 ..... Thanks! 👍

[jdgleaver]

Yes, the repos should be synced. I have a couple of other things I need to look at, and I'm supposed to be on holiday this week (so I'm in trouble with the family if I spend too much time alone on the computer!), but I shall certainly add this to my TODO list - hopefully should be fairly straightforward :)