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BBC Micro Elite

Charts: TT103

Name: TT103 [View in context] Type: Subroutine Category: Charts Summary: Draw a small set of crosshairs on a chart
Draw a small set of crosshairs on a galactic chart at the coordinates in (QQ9, QQ10).
.TT103 { LDA QQ11 \ If this is a space view, return from the subroutine BEQ TT180 \ (as TT180 contains an RTS), as there are no moveable \ crosshairs in space BMI TT105 \ If this is the Short-range Chart screen, jump to TT105 LDA QQ9 \ Store the crosshairs x-coordinate in QQ19 STA QQ19 LDA QQ10 \ Halve the crosshairs y-coordinate and store it in QQ19 LSR A \ (we halve it because the Long-range Chart is half as STA QQ19+1 \ high as it is wide) LDA #4 \ Set QQ19+2 to 4 denote crosshairs of size 4 STA QQ19+2 JMP TT15 \ Jump to TT15 to draw crosshairs of size 4 at the \ crosshairs coordinates, returning from the subroutine \ using a tail call }