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Revs on the BBC Micro

Track geometry: MultiplyHeight

Name: MultiplyHeight [Show more] Type: Subroutine Category: Track geometry Summary: Multiply the height above ground of a specified track segment by A
Context: See this subroutine in context in the source code References: This subroutine is called as follows: * ApplyElevation (Part 3 of 5) calls MultiplyHeight * ApplyElevation (Part 5 of 5) calls MultiplyHeight

For segment vector Y, calculate: A = A * yTrackSegmentI flipping the sign if we are facing backwards. Arguments: A The number to multiply the height by Y Index of the segment vector to multiply Returns: N flag Set according to the result in A
.MultiplyHeight STA U \ Set U to the multiplication factor in A LDA yTrackSegmentI,Y \ Store the sign of the height * directionFacing on EOR directionFacing \ the stack PHP LDA yTrackSegmentI,Y \ Set A to the track height in the Y-th yTrackSegmentI JSR Absolute8Bit \ Set A = |A| \ = |yTrackSegmentI| JSR Multiply8x8 \ Set (A T) = A * U \ = U * |yTrackSegmentI| PLP \ Set the N flag to the sign of yTrackSegmentI * \ directionFacing, so this will be set if the height \ sign is different to bit 7 of directionFacing, clear \ if the height sign matches bit 7 of directionFacing JSR Absolute8Bit \ Give A the sign in the N flag RTS \ Return from the subroutine