Skip to navigation

⌂ ∞ ▽ Revs on the BBC Micro

Maths (Geometry): AddCoords

       Name: AddCoords                                               [Show more]
       Type: Subroutine
   Category: Maths (Geometry)
    Summary: Add to a specified coordinate variable

    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * MultiplyCoords calls AddCoords
             * SubtractCoords calls AddCoords




 This routine adds (U T) to the specified 16-bit variable.



 Arguments:

   Y                    Offset of the variable to update:

                          * 3 = xAcceleration

                          * 4 = zAcceleration

                          * 6 = xPlayerAccel

                          * 9 = zVelocity

                          * 12 = zTyreForceNose

                          * 14 = xSteeringForce



.AddCoords

 LDA xPlayerSpeedHi,Y   \ Add (U T) to (xPlayerSpeedTop xPlayerSpeedHi)
 CLC                    \
 ADC T                  \ starting with the low bytes
 STA xPlayerSpeedHi,Y

 LDA xPlayerSpeedTop,Y  \ And then the high bytes
 ADC U
 STA xPlayerSpeedTop,Y

 RTS                    \ Return from the subroutine