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⌂ ∞ Elite on the BBC Micro and NES

Charts: TT22

[NES version, Bank 0]

       Name: TT22                                                    [Show more]
       Type: Subroutine
   Category: Charts
    Summary: Show the Long-range Chart

    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * RedrawCurrentView calls TT22
             * TT102 calls TT22
             * TT114 calls TT22




.TT22

 LDA #$8D               ; Clear the screen and set the view type in QQ11 to $8D
 JSR TT66               ; (Long-range Chart)

 LDA #77                ; Set the screen height variables for a screen height of
 JSR SetScreenHeight    ; 154 (i.e. 2 * 77)

 LDA #7                 ; Move the text cursor to column 7
 STA XC

 JSR TT81               ; Set the seeds in QQ15 to those of system 0 in the
                        ; current galaxy (i.e. copy the seeds from QQ21 to QQ15)

 LDA #199               ; Print recursive token 39 ("GALACTIC CHART{galaxy
 JSR NLIN3              ; number right-aligned to width 3}") on the top row

 LDA #152               ; Draw a screen-wide horizontal line at pixel row 152
 JSR NLIN2              ; for the bottom edge of the chart, so the chart itself
                        ; is 128 pixels high, starting on row 24 and ending on
                        ; row 151

 JSR FadeAndHideSprites ; Fade the screen to black and hide all sprites, so we
                        ; can update the screen while it's blacked-out

 JSR TT14               ; Call TT14 to draw a circle with crosshairs at the
                        ; current system's galactic coordinates

 LDX #0                 ; We're now going to plot each of the galaxy's systems,
                        ; so set up a counter in X for each system, starting at
                        ; 0 and looping through to 255

.TT83

 STX XSAV               ; Store the counter in XSAV

 LDA QQ15+3             ; Fetch the s1_hi seed into A, which gives us the
                        ; galactic x-coordinate of this system

 LSR A                  ; Set X = s1_hi - (A / 4) + 31
 LSR A                  ;       = s1_hi - (s1_hi / 4) + 31
 STA T1                 ;       = 31 + 0.75 * s1_hi
 LDA QQ15+3             ;
 SEC                    ; So this scales the x-coordinate from a range of 0 to
 SBC T1                 ; 255 into a range from 31 to 222, so it fits nicely
 CLC                    ; into the Long-range Chart
 ADC #31
 TAX

 LDY QQ15+4             ; Fetch the s2_lo seed and set bits 4 and 6, storing the
 TYA                    ; result in ZZ to give a random number between 80 and
 ORA #%01010000         ; (but which will always be the same for this system).
 STA ZZ                 ; We use this value to determine the size of the point
                        ; for this system on the chart by passing it as the
                        ; distance argument to the PIXEL routine below

 LDA QQ15+1             ; Fetch the s0_hi seed into A, which gives us the
                        ; galactic y-coordinate of this system

 LSR A                  ; Set A = (s0_hi - (A / 4)) / 2 + 32
 LSR A                  ;       = (s0_hi - (s0_hi / 4)) / 2 + 32
 STA T1                 ;       = 32 + 0.375 * s1_hi
 LDA QQ15+1             ;
 SEC                    ; So this scales the y-coordinate from a range of 0 to
 SBC T1                 ; 255 into a range from 32 to 127, so it fits nicely
 LSR A                  ; into the Long-range Chart
 CLC
 ADC #32

 STA Y1                 ; Store the y-coordinate in Y1 (though this gets
                        ; overwritten by the call to DrawDash, so this has no
                        ; effect)

 JSR DrawDash           ; Draw a 2-pixel dash at pixel coordinate (X, A)

 JSR TT20               ; We want to move on to the next system, so call TT20
                        ; to twist the three 16-bit seeds in QQ15

 LDX XSAV               ; Restore the loop counter from XSAV

 INX                    ; Increment the counter

 BNE TT83               ; If X > 0 then we haven't done all 256 systems yet, so
                        ; loop back up to TT83

 LDA #3                 ; Set K+2 = 3 to pass to DrawSmallBox as the text row
 STA K+2                ; on which to draw the top-left corner of the small box

 LDA #4                 ; Set K+3 = 4 to pass to DrawSmallBox as the text column
 STA K+3                ; on which to draw the top-left corner of the small box

 LDA #25                ; Set K = 25 to pass to DrawSmallBox as the width of the
 STA K                  ; small box

 LDA #14                ; Set K+1 = 14 to pass to DrawSmallBox as the height of
 STA K+1                ; the small box

 JSR DrawSmallBox_b3    ; Draw a box around the chart, with the top-left corner
                        ; at (3, 4), a height of 14 rows, and a width of 25 rows

 LDA QQ9                ; Set QQ19 to the selected system's x-coordinate
 STA QQ19

 LDA QQ10               ; Set QQ19+1 to the selected system's y-coordinate,
 LSR A                  ; halved to fit it into the chart
 STA QQ19+1

 LDA #4                 ; Set QQ19+2 to size 4 for the crosshairs size
 STA QQ19+2

 JSR TT103              ; Draw small crosshairs at coordinates (QQ9, QQ10),
                        ; which will draw the crosshairs at our current home
                        ; system

 LDA #$9D               ; Set the view type in QQ11 to $00 (Long-range Chart
 STA QQ11               ; with the normal font loaded)

 LDA #143               ; Set the number of pixel rows in the space view to 143,
 STA Yx2M1              ; so the screen height is correctly set for the
                        ; Short-range Chart in case we switch to it using the
                        ; icon in the icon bar (which toggles between the two
                        ; charts)

 JMP UpdateView         ; Update the view, returning from the subroutine using
                        ; a tail call