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⌂ ∞ ▽ Elite on the 6502

Charts: TT103

[Commodore 64 version]

       Name: TT103                                                   [Show more]
       Type: Subroutine
   Category: Charts
    Summary: Draw a small set of crosshairs on a chart

    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * hm calls TT103
             * HME2 calls TT103
             * TT102 calls TT103
             * TT16 calls TT103
             * TT23 calls TT103




 Draw a small set of crosshairs on a galactic chart at the coordinates in
 (QQ9, QQ10).



.TT103

 LDA QQ11               ; Fetch the current view type into A

 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