Dashboard: UpdateIndicator (Part 13 of 15)

       Name: UpdateIndicator (Part 13 of 15)                         [Show more]
       Type: Subroutine
   Category: Dashboard
    Summary: Calculations for the rudder indicator (indicator 9)
    Context: See this subroutine in context in the source code
 References: No direct references to this subroutine in this source file


 This section takes the rudder position from rudderPosition and reduces it to
 the range -8 to +8, before passing it to DrawIndicatorBar to update the rudder
 indicator.


.uind24

                        \ If we get here then the indicator number in X is 9

 LDX #1                 \ Set X = 1 so the current value of the indicator gets
                        \ stored in yJoyCoord+1 in DrawIndicatorBar

 LDA #128               \ Set S = 128, to denote that when we fall through into
 STA S                  \ DrawIndicatorBar below, joyCoord is the y-coordinate,
                        \ so we draw the indicator's vertical bar from point
                        \ (H + W, joyCoord)

 LDA #80                \ Set W = 80 to use as the centre y-coordinate for the
 STA W                  \ rudder indicator (i.e. the centre bar)

 LDA rudderPosition     \ Set A = rudderPosition

 SEC                    \ Set the C flag so the following call to ScaleSigned
                        \ divides the rudder value by 16

 JSR ScaleSigned        \ Scale the value in A down by a factor of 16, retaining
                        \ the sign and being sensitive to small values

 STA H                  \ Store the scaled value in H, which has now been
                        \ reduced from the range -128 to 127 down to -8 to +8,
                        \ to use as the x-coordinate offset from the centre of
                        \ the indicator in DrawIndicatorBar

 LDY #163               \ Set Y = 163 to use as the y-coordinate of the top of
                        \ the vertical bar

 LDA #11                \ Set A = 11 to set the height of the vertical bar at 11
                        \ pixels

 BNE DrawIndicatorBar   \ Jump to DrawIndicatorBar to update indicator 9 by
                        \ drawing a vertical bar of height 11 pixels with
                        \ the top at (80 + H, 163)