SixtyPical/include/c64/joystick.60p

byte joy2 @ $dc00

word delta

// Read the joystick and compute the delta it represents
// in a row-based 40-column grid like the C64's screen.

define read_stick routine
  inputs joy2
  outputs delta
  trashes a, x, z, n
{
    ld x, joy2
    ld a, x
    and a, 1                   // up
    if z {
        copy $ffd8, delta      // -40
    } else {
        ld a, x
        and a, 2               // down
        if z {
            copy word 40, delta
        } else {
            ld a, x
            and a, 4               // left
            if z {
                copy $ffff, delta  // -1
            } else {
                ld a, x
                and a, 8           // right
                if z {
                    copy word 1, delta
                } else {
                    copy word 0, delta
                }
            }
        }
    }
}

// You can repeatedly (i.e. as part of actor logic or an IRQ handler)
// call this routine.
// Upon return, if carry is set, the button was pressed then released.

define check_button routine
  inputs joy2
  outputs c
  trashes a, z, n
  static byte button_down : 0
{
    ld a, button_down
    if z {
        ld a, joy2
        and a, $10
        if z {
            ld a, 1
            st a, button_down
        }
        st off, c
    } else {
        ld a, joy2
        and a, $10
        if not z {
            ld a, 0
            st a, button_down
            st on, c
        } else {
            st off, c
        }
    }
}