Extra tracks: HookJoystick (Part 1 of 3)

       Name: HookJoystick (Part 1 of 3)                              [Show more]
       Type: Subroutine
   Category: Extra tracks
    Summary: Apply enhanced joystick steering to specific track sections
  Deep dive: Secrets of the extra tracks
             Code hooks in the extra tracks
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * newContentHi calls HookJoystick
             * newContentLo calls HookJoystick


 This routine is called from ProcessDrivingKeys to zero the playerDrift flag
 when the player is in one of the specified track sections, which has the
 effect of cancelling drift:

   * Section 2: if the player is in segment 0 or 1, cancel drift

   * Section 21: cancel drift

 In addition, scale the steering in the following sections to make it easier
 to steer when using a joystick:

   * Section 2: scale the steering by 1.48

   * Section 20: scale the steering by 1.16

   * Section 21: scale the steering by 1.16

 Specifically, the scaling is applied as follows:

   (A T) = scale_factor * x-axis ^ 2

 which replaces this existing code in ProcessDrivingKeys:

   (A T) = x-axis^2


 Arguments:

   U                    The joystick x-axis high byte


.HookJoystick

 LDY currentPlayer      \ Set A to the track section number * 8 for the current
 LDA objTrackSection,Y  \ player

 CMP #40                \ If the track section <> 16 (i.e. section 2), jump to
 BNE joys2              \ joys2 to keep checking

 LDA objSectionSegmt,Y  \ Set A = objSectionSegmt, which keeps track of the
                        \ player's segment number in the current track section

 CMP #2                 \ If A < 2, jump to joys1
 BCC joys1

 LSR playerDrift        \ A = 0 or 1, which means the player is in one of the
                        \ first two segments in the section so clear bit 7 of
                        \ playerDrift to denote that the player is not drifting
                        \ sideways (i.e. cancel any drift)

.joys1

 LDY #220               \ Set Y = 220 so we scale the steering by 1.48

 JMP joys6              \ Jump to part 3 to scale the steering

.joys2

 JMP joys3              \ Jump to part 2

 EQUB &4C, &1B          \ These bytes appear to be unused
 EQUB &46