Flight model: ProcessLanding (Part 3 of 7)

       Name: ProcessLanding (Part 3 of 7)                            [Show more]
       Type: Subroutine
   Category: Flight model
    Summary: If we are taxiing, restrict the plane's vertical movement and roll
  Deep dive: Take-offs and landings
    Context: See this subroutine in context in the source code
 References: No direct references to this subroutine in this source file


 This part checks whether we are in the process of landing, and if so we jump
 to part 6. Otherwise we have already landed and are taxiing, so we set the
 plane's height, vertical velocity and roll accordingly.


                        \ If we get here then the plane is close enough to the
                        \ ground to be touching down

 LDX L                  \ Fetch the current value of onGround

 BEQ clan10             \ If L is zero then we are not on the ground, so jump
                        \ to clan10 to skip to part 6

                        \ If we get here then we are already on the ground, so
                        \ we are in the process of landing

 STA yPlaneLo           \ Set the low byte of the plane's y-coordinate to A,
                        \ which contains the value of yLandingGear, so this sets
                        \ the plane's height to the correct value for taxiing,
                        \ i.e. the distance between the cockpit and the lowest
                        \ part of the plane

 LDX yVelocityTop       \ If the top byte of the plane's vertical velocity is
 BPL clan5              \ positive, skip the following

 LDX #&8A               \ We are on the ground and the plane's vertical velocity
 JSR ResetVariable      \ is negative, so set (yVelocityTop yVelocityHi) = 0 as
                        \ the plane can't travel down into the ground

.clan5

 LDX #&EC               \ Set (zRotationHi zRotationLo) = 0 to set the plane to
 JSR ResetVariable      \ the horizontal position (i.e. zero roll angle)

 LDX #&02               \ Set (zTurnTop zTurnHi) = 0 to stop the plane turning
 JSR ResetVariable      \ around the z-axis (i.e. stop the plane rolling)

 LDX ucStatus           \ If ucStatus is non-zero then the undercarriage is
 BNE clan9              \ down, so jump to clan9