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⌂ ∞ ▽ Elite on the BBC Micro and NES

Dashboard: COMPAS

[BBC Master version]

       Name: COMPAS                                                  [Show more]
       Type: Subroutine
   Category: Dashboard
    Summary: Update the compass

    Context: See this subroutine in context in the source code
 Variations: See code variations for this subroutine in the different versions
 References: This subroutine is called as follows:
             * DIALS (Part 4 of 4) calls COMPAS




.COMPAS

 JSR DOT                \ Call DOT to redraw (i.e. remove) the current compass
                        \ dot

 LDA SSPR               \ If we are inside the space station safe zone, jump to
 BNE SP1                \ SP1 to draw the space station on the compass

 JSR SPS1               \ Otherwise we need to draw the planet on the compass,
                        \ so first call SPS1 to calculate the vector to the
                        \ planet and store it in XX15

 JMP SP2                \ Jump to SP2 to draw XX15 on the compass, returning
                        \ from the subroutine using a tail call