Extra tracks: HookJoystick (Part 1 of 2)

       Name: HookJoystick (Part 1 of 2)                              [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 scale the steering in the
 following sections to make it easier to steer when using a joystick:

   * Section 8: scale the steering by 1.28

   * Section 11: scale the steering by 1.37

   * Section 26: scale the steering by 1.25

 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

   A                    The joystick x-axis high byte

   Z flag               Set if A= 0


.HookJoystick

 PHP                    \ Store the status flags and A on the stack, so we can
 PHA                    \ use them in the steering calculation

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

 LDY #181               \ Set Y= 181 so by default we scale the steering by
                        \ 1.00

 CMP #88                \ If the track section <> 88 (i.e. section 11), jump to
 BNE joys1              \ joys1 to keep checking

 LDY #212               \ Set Y= 212 so we scale the steering by 1.37

.joys1

 CMP #64                \ If the track section <> 64 (i.e. section 8), jump to
 BNE joys2              \ joys2 to keep checking

 LDY #205               \ Set Y= 205 so we scale the steering by 1.28

.joys2

 CMP #208               \ If the track section <> 208 (i.e. section 26), jump to
 BNE joys3              \ joys3 to keep checking

 LDY #202               \ Set Y= 202 so we scale the steering by 1.25

.joys3

 TYA                    \ Set A= Y
                        \
                        \ So A is 181, 202, 205 or 212

 JMP joys4              \ Jump to part 2 to scale the steering

 EQUB &B5, &B8          \ These bytes appear to be unused