Version analysis of WPLS

       Name: WPLS
       Type: Subroutine
   Category: Drawing suns
    Summary: Remove the sun from the screen
  Deep dive: Drawing the sun


 We do this by redrawing it using the lines stored in the sun line heap when
 the sun was originally drawn by the SUN routine.


 Arguments:

   SUNX(1 0)            The x-coordinate of the vertical centre axis of the sun

Cassette, Flight, Master
 Other entry points:

   WPLS-1               Contains an RTS

.WPLS

Cassette, Flight, Master
Docked
6502SP
 LDA LSX                \ If LSX < 0, the sun line heap is empty, so return from
 BMI WPLS-1             \ the subroutine (as WPLS-1 contains an RTS)
 LDA LSX                \ If LSX < 0, the sun line heap is empty, so return from
 BMI PL44               \ the subroutine (as PL44 contains a CLC and RTS)
 LDA LSX                \ If LSX < 0, the sun line heap is empty, so return from
 BMI WP1                \ the subroutine (as WP1 contains an RTS)

 LDA SUNX               \ Set YY(1 0) = SUNX(1 0), the x-coordinate of the
 STA YY                 \ vertical centre axis of the sun that's currently on
 LDA SUNX+1             \ screen
 STA YY+1

 LDY #2*Y-1             \ #Y is the y-coordinate of the centre of the space
                        \ view, so this sets Y as a counter for the number of
                        \ lines in the space view (i.e. 191), which is also the
                        \ number of lines in the LSO block

.WPL2

 LDA LSO,Y              \ Fetch the Y-th point from the sun line heap, which
                        \ gives us the half-width of the sun's line on this line
                        \ of the screen

 BEQ P%+5               \ If A = 0, skip the following call to HLOIN2 as there
                        \ is no sun line on this line of the screen

 JSR HLOIN2             \ Call HLOIN2 to draw a horizontal line on pixel line Y,
                        \ with centre point YY(1 0) and half-width A, and remove
                        \ the line from the sun line heap once done

 DEY                    \ Decrement the loop counter

 BNE WPL2               \ Loop back for the next line in the line heap until
                        \ we have gone through the entire heap

 DEY                    \ This sets Y to &FF, as we end the loop with Y = 0

 STY LSX                \ Set LSX to &FF to indicate the sun line heap is empty

Cassette, Flight, Docked, Master
6502SP
 RTS                    \ Return from the subroutine
 JMP HBFL               \ Call HBFL to send the contents of the horizontal line
                        \ buffer to the I/O processor for drawing on-screen,
                        \ returning from the subroutine using a tail call