Drawing circles: TT14

       Name: TT14                                                    [Show more]
       Type: Subroutine
   Category: Drawing circles
    Summary: Draw a circle with crosshairs on a chart
    Context: See this subroutine in context in the source code
 Variations: See code variations for this subroutine in the different versions
 References: This subroutine is called as follows:
             * TT22 calls TT14
             * TT23 calls TT14


 Draw a circle with crosshairs at the current system's galactic coordinates.


.TT126

 LDA #104               \ Set QQ19 = 104, for the x-coordinate of the centre of
 STA QQ19               \ the fixed circle on the Short-range Chart

 LDA #90                \ Set QQ19+1 = 90, for the y-coordinate of the centre of
 STA QQ19+1             \ the fixed circle on the Short-range Chart

 LDA #16                \ Set QQ19+2 = 16, the size of the crosshairs on the
 STA QQ19+2             \ Short-range Chart

 JSR TT15               \ Draw the set of crosshairs defined in QQ19, at the
                        \ exact coordinates as this is the Short-range Chart

 LDA QQ14               \ Set K to the fuel level from QQ14, so this can act as
 STA K                  \ the circle's radius (70 being a full tank)

 JMP TT128              \ Jump to TT128 to draw a circle with the centre at the
                        \ same coordinates as the crosshairs, (QQ19, QQ19+1),
                        \ and radius K that reflects the current fuel levels,
                        \ returning from the subroutine using a tail call

.TT14

 LDA QQ11               \ If the current view is the Short-range Chart, which
 BMI TT126              \ is the only view with bit 7 set, then jump up to TT126
                        \ to draw the crosshairs and circle for that view

                        \ Otherwise this is the Long-range Chart, so we draw the
                        \ crosshairs and circle for that view instead

 LDA QQ14               \ Set K to the fuel level from QQ14 divided by 4, so
 LSR A                  \ this can act as the circle's radius (70 being a full
 LSR A                  \ tank, which divides down to a radius of 17)
 STA K

 LDA QQ0                \ Set QQ19 to the x-coordinate of the current system,
 STA QQ19               \ which will be the centre of the circle and crosshairs
                        \ we draw

 LDA QQ1                \ Set QQ19+1 to the y-coordinate of the current system,
 LSR A                  \ halved because the galactic chart is half as high as
 STA QQ19+1             \ it is wide, which will again be the centre of the
                        \ circle and crosshairs we draw

 LDA #7                 \ Set QQ19+2 = 7, the size of the crosshairs on the
 STA QQ19+2             \ Long-range Chart

 JSR TT15               \ Draw the set of crosshairs defined in QQ19, which will
                        \ be drawn 24 pixels to the right of QQ19+1

 LDA QQ19+1             \ Add 24 to the y-coordinate of the crosshairs in QQ19+1
 CLC                    \ so that the centre of the circle matches the centre
 ADC #24                \ of the crosshairs
 STA QQ19+1

                        \ Fall through into TT128 to draw a circle with the
                        \ centre at the same coordinates as the crosshairs,
                        \ (QQ19, QQ19+1), and radius K that reflects the
                        \ current fuel levels