.uind20 \ If we get here then the indicator number in X is 7 LDY #0 \ Set Y = 0, to use as an argument to ArtificialHorizon STY K \ Set K = 0, to use as an argument to ArtificialHorizon STY R \ Set R = 0, to use as the first guess for the direction \ of the horizon line (we will change it below if \ required) JSR ArtificialHorizon \ Call ArtificialHorizon with K = 0, Y = 0 to calculate \ the x-coordinate of the line's starting point in A CLC \ Clear the C flag (this appears to have no effect) STA S \ Set H = S, so this sets the x-coordinate of the line's \ starting point LDY #3 \ Set Y = 3 JSR ArtificialHorizon \ Call ArtificialHorizon with K = 0, Y = 3 to calculate \ the y-coordinate of the line's starting point in A STA H \ Set H = A, so this sets the y-coordinate of the line's \ starting point LDY #0 \ Set Y = 0, to use as an argument to ArtificialHorizon LDA #1 \ Set K = 1, to use as an argument to ArtificialHorizon STA K JSR ArtificialHorizon \ Call ArtificialHorizon with K = 1, Y = 0 to calculate \ the x-delta of the line SEC \ Set A = A - S SBC S \ = A - x-coordinate of start BPL uind21 \ If A is positive, the sign of the x-delta is correct, \ so jump to uind21 STA T \ The returned x-delta is negative, so store it in T so \ we can negate it below LDA #%10000000 \ Set bit 7 of R to indicate that the x-delta for the STA R \ line is negative and the y-delta is positive LDA #0 \ Set A = 0 - T SEC \ SBC T \ so the x-delta in A is now positive .uind21 CLC \ Set W = A + 1 ADC #1 \ STA W \ so this sets the line's x-delta, making sure the line \ is at least one pixel wide LDY #3 \ Set Y = 3, to use as an argument to ArtificialHorizon JSR ArtificialHorizon \ Call ArtificialHorizon with K = 1, Y = 3 to calculate \ the y-delta of the line SEC \ Set A = A - H SBC H \ = A - y-coordinate of start BPL uind22 \ If A is positive, the sign of the y-delta is correct, \ so jump to uind22 STA T \ The returned y-delta is negative, so store it in T so \ we can negate it below LDA #%01000000 \ Set bit 6 of R to indicate that the y-delta is ORA R \ negative, making sure to leave bit 7 as it is STA R LDA #0 \ Set A = A - T SEC \ SBC T \ so the y-delta in A is now positive .uind22 CLC \ Set G = A + 1 ADC #1 \ STA G \ so this sets the line's y-delta, making sure the line \ is at least 1 pixel tall LDA S \ Set S = S + 53 CLC \ ADC #53 \ so the start x-coordinate is moved to be relative to STA S \ the centre of the artificial horizon indicator, which \ is at (53, 160 + 29) LDA H \ Set H = H - 29 CLC \ ADC #227 \ so the start y-coordinate is moved to be relative to STA H \ the centre of the artificial horizon indicator, which \ is at (53, 160 + 29) JMP DrawIndicatorLine \ Draw the new artificial horizon, returning from the \ subroutine using a tail callName: UpdateIndicator (Part 11 of 15) [Show more] Type: Subroutine Category: Dashboard Summary: Calculations for the artificial horizon (indicator 7)Context: See this subroutine in context in the source code References: No direct references to this subroutine in this source file
Calculations for the artificial horizon's line vector are all performed in the ArtificialHorizon routine, which calculates the starting coordinates and deltas for the vector line. This routine simply takes those results, sets the direction bits for the line, and moves the starting point so the line is centred on the artificial horizon indicator.
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Subroutine ArtificialHorizon (category: Dashboard)
Vector line calculation for the artificial horizon on indicator 7
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Subroutine DrawIndicatorLine (category: Drawing lines)
Draw a line on indicators 0 to 7, i.e. a dial hand (0-6) or an artificial horizon (7)
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Label uind21 is local to this routine
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Label uind22 is local to this routine