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Elite on the BBC Micro

Charts: TT22 (Master version)

Name: TT22 [View in context] Type: Subroutine [Compare versions] Category: Charts Summary: Show the Long-range Chart (red key f4)
.TT22 LDA #64 \ Clear the top part of the screen, draw a white border, JSR TT66 \ and set the current view type in QQ11 to 32 (Long- \ range Chart) LDA #16 \ Switch to the mode 1 palette for the trade view, which JSR DOVDU19 \ is yellow (colour 1), magenta (colour 2) and white \ (colour 3) LDA #CYAN \ Switch to colour 3, which is white in the chart view STA COL 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 TT27 \ number right-aligned to width 3}") JSR NLIN \ Draw a horizontal line at pixel row 23 to box in the \ title and act as the top frame of the chart, and move \ the text cursor down one line LDA #153 \ Move the text cursor down one line and draw a JSR NLIN2-2 \ screen-wide horizontal line at pixel row 153 for the \ bottom edge of the chart, so the chart itself is 128 \ pixels high, starting on row 24 and ending on row 153 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 LDX QQ15+3 \ Fetch the s1_hi seed into X, which gives us the \ galactic x-coordinate of this system 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 #YELLOW \ Switch to colour 1, which is yellow STA COL LDA QQ15+1 \ Fetch the s0_hi seed into A, which gives us the \ galactic y-coordinate of this system JSR SCALEY \ We halve the y-coordinate because the galaxy in \ in Elite is rectangular rather than square, and is \ twice as wide (x-axis) as it is high (y-axis), so the \ chart is 256 pixels wide and 128 high \ \ The call to SCALEY simply does an LSR A, but having \ this call instruction here would enable different \ scaling to be applied by altering the SCALE routines. \ This code is left over from the conversion to other \ platforms, where the scale factor might need to be \ different CLC \ Add 24 to the halved y-coordinate in A (as the top of ADC #24 \ the chart is on pixel row 24, just below the line we \ drew on row 23 above) JSR PIXEL \ Call PIXEL to draw a point at (X, A), with the size of \ the point dependent on the distance specified in ZZ \ (so a high value of ZZ will produce a 1-pixel point, \ a medium value will produce a 2-pixel dash, and a \ small value will produce a 4-pixel square) 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 QQ9 \ Set QQ19 to the selected system's x-coordinate JSR SCALEX \ STA QQ19 \ The call to SCALEX has no effect as it only contains \ an RTS, but having this call instruction here would \ enable different scaling to be applied by altering \ the SCALE routines. This code is left over from the \ conversion to other platforms, where the scale factor \ might need to be different LDA QQ10 \ Set QQ19+1 to the selected system's y-coordinate, JSR SCALEY \ halved to fit it into the chart STA QQ19+1 \ \ The call to SCALEY simply does an LSR A, but having \ this call instruction here would enable different \ scaling to be applied by altering the SCALE routines. \ This code is left over from the conversion to other \ platforms, where the scale factor might need to be \ different LDA #4 \ Set QQ19+2 to size 4 for the crosshairs size STA QQ19+2 LDA #GREEN \ Switch to stripe 3-1-3-1, which is white/yellow in the STA COL \ chart view \ Fall through into TT15 to draw crosshairs of size 4 at \ the selected system's coordinates