The ResetRadar subroutine - Aviator on the BBC Micro

       Name: ResetRadar                                              [Show more]
       Type: Subroutine
   Category: Dashboard
    Summary: Reset the radar display
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * ScoreHitPoints calls ResetRadar


.ResetRadar

 LDA #80                \ Set xPointLo = 80, so we don't draw a new alien on the
 STA xPointLo           \ radar (as this coordinate is off the radar)

 LDA #1                 \ Set alien = 1, so we remove the alien from the radar
 STA alien              \ rather than the runway when we call DrawRadarBlip

 STA xPointHi           \ Set xPointHi = 1, so the value in xPointLo is treated
                        \ as positive

 JSR DrawRadarBlip      \ Remove the current dot from the radar, but don't draw
                        \ a new one, as xPointLo is off-radar

 LDY #33                \ Reset object 33's coordinates (the flying alien) to
 JSR SetObjectToOrigin  \ (0, 0, 0)

 RTS                    \ Return from the subroutine

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Subroutine DrawRadarBlip (category: Dashboard)

Draw a blip on the radar (runway or alien)

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Subroutine SetObjectToOrigin (category: 3D geometry)

Set an object's coordinates to (0, 0, 0)

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Variable alien in workspace Main variable workspace

Temporary storage, used as a flag to indicate the alien when updating the radar (shares a memory location with the objCount variable)

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Variable xPointHi (category: 3D geometry)

High byte of the x-coordinate for a point

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Variable xPointLo in workspace Main variable workspace

The low byte of the x-coordinate for the point with ID X is at xPointLo,X