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BBC Micro Elite

Charts: TT23

Name: TT23 [View in context] Type: Subroutine Category: Charts Summary: Show the Short-range Chart (red key f5)
.TT23 { LDA #128 \ Clear the top part of the screen, draw a white border, JSR TT66 \ and set the current view type in QQ11 to 128 (Short- \ range Chart) LDA #7 \ Move the text cursor to column 7 STA XC LDA #190 \ Print recursive token 30 ("SHORT RANGE CHART") and JSR NLIN3 \ draw a horizontal line at pixel row 19 to box in the \ title JSR TT14 \ Call TT14 to draw a circle with crosshairs at the \ current system's galactic coordinates JSR TT103 \ Draw small crosshairs at coordinates (QQ9, QQ10), \ i.e. at the selected system 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 #0 \ Set A = 0, which we'll use below to zero out the INWK \ workspace STA XX20 \ We're about to start working our way through each of \ the galaxy's systems, so set up a counter in XX20 for \ each system, starting at 0 and looping through to 255 LDX #24 \ First, though, we need to zero out the 25 bytes at \ INWK so we can use them to work out which systems have \ room for a label, so set a counter in X for 25 bytes .EE3 STA INWK,X \ Set the X-th byte of INWK to zero DEX \ Decrement the counter BPL EE3 \ Loop back to EE3 for the next byte until we've zeroed \ all 25 bytes \ We now loop through every single system in the galaxy \ and check the distance from the current system whose \ coordinates are in (QQ0, QQ1). We get the galactic \ coordinates of each system from the system's seeds, \ like this: \ \ x = w1_hi (which is stored in QQ15+3) \ y = w0_hi (which is stored in QQ15+1) \ \ so the following loops through each system in the \ galaxy in turn and calculates the distance between \ (QQ0, QQ1) and (w1_hi, w0_hi) to find the closest one .TT182 LDA QQ15+3 \ Set A = w1_hi - QQ0, the horizontal distance between SEC \ (w1_hi, w0_hi) and (QQ0, QQ1) SBC QQ0 BCS TT184 \ If a borrow didn't occur, i.e. w1_hi >= QQ0, then the \ result is positive, so jump to TT184 and skip the \ following two instructions EOR #&FF \ Otherwise negate the result in A, so A is always ADC #1 \ positive (i.e. A = |w1_hi - QQ0|) .TT184 CMP #20 \ If the horizontal distance in A is >= 20, then this BCS TT187 \ system is too far away from the current system to \ appear in the Short-range Chart, so jump to TT187 to \ move on to the next system LDA QQ15+1 \ Set A = w0_hi - QQ1, the vertical distance between SEC \ (w1_hi, w0_hi) and (QQ0, QQ1) SBC QQ1 BCS TT186 \ If a borrow didn't occur, i.e. w0_hi >= QQ1, then the \ result is positive, so jump to TT186 and skip the \ following two instructions EOR #&FF \ Otherwise negate the result in A, so A is always ADC #1 \ positive (i.e. A = |w0_hi - QQ1|) .TT186 CMP #38 \ If the vertical distance in A is >= 38, then this BCS TT187 \ system is too far away from the current system to \ appear in the Short-range Chart, so jump to TT187 to \ move on to the next system \ This system should be shown on the Short-range Chart, \ so now we need to work out where the label should go, \ and set up the various variables we need to draw the \ system's filled circle on the chart LDA QQ15+3 \ Set A = w1_hi - QQ0, the horizontal distance between SEC \ this system and the current system, where |A| < 20. SBC QQ0 \ Let's call this the x-delta, as it's the horizontal \ difference between the current system at the centre of \ the chart, and this system (and this time we keep the \ sign of A, so it can be negative if it's to the left \ of the chart's centre, or positive if it's to the \ right) ASL A \ Set XX12 = 104 + x-delta * 4 ASL A \ ADC #104 \ 104 is the x-coordinate of the centre of the chart, STA XX12 \ so this sets XX12 to the centre 104 +/- 76, the pixel \ x-coordinate of this system LSR A \ Move the text cursor to column x-delta / 2 + 1 LSR A \ which will be in the range 1-10 LSR A STA XC INC XC LDA QQ15+1 \ Set A = w0_hi - QQ1, the vertical distance between SEC \ this system and the current system, where |A| < 38. SBC QQ1 \ Let's call this the y-delta, as it's the vertical \ difference between the current system at the centre of \ the chart, and this system (and this time we keep the \ sign of A, so it can be negative if it's above the \ chart's centre, or positive if it's below) ASL A \ Set K4 = 90 + y-delta * 2 ADC #90 \ STA K4 \ 90 is the y-coordinate of the centre of the chart, \ so this sets K4 to the centre 90 +/- 74, the pixel \ y-coordinate of this system LSR A \ Set Y = K4 / 8, so Y contains the number of the text LSR A \ row that contains this system LSR A TAY \ Now to see if there is room for this system's label. \ Ideally we would print the system name on the same \ text row as the system, but we only want to print one \ label per row, to prevent overlap, so now we check \ this system's row, and if that's already occupied, \ the row above, and if that's already occupied, the \ row below... and if that's already occupied, we give \ up and don't print a label for this system LDX INWK,Y \ If the value in INWK+Y is 0 (i.e. the text row BEQ EE4 \ containing this system does not already have another \ system's label on it), jump to EE4 to store this \ system's label on this row INY \ If the value in INWK+Y+1 is 0 (i.e. the text row below LDX INWK,Y \ the one containing this system does not already have BEQ EE4 \ another system's label on it), jump to EE4 to store \ this system's label on this row DEY \ If the value in INWK+Y-1 is 0 (i.e. the text row above DEY \ the one containing this system does not already have LDX INWK,Y \ another system's label on it), fall through into to BNE ee1 \ EE4 to store this system's label on this row, \ otherwise jump to ee1 to skip printing a label for \ this system (as there simply isn't room) .EE4 STY YC \ Now to print the label, so move the text cursor to row \ Y (which contains the row where we can print this \ system's label) CPY #3 \ If Y < 3, then the label would clash with the chart BCC TT187 \ title, so jump to TT187 to skip printing the label DEX \ We entered the EE4 routine with X = 0, so this stores STX INWK,Y \ &FF in INWK+Y, to denote that this row is now occupied \ so we don't try to print another system's label on \ this row LDA #%10000000 \ Set bit 7 of QQ17 to switch to Sentence Case STA QQ17 JSR cpl \ Call cpl to print out the system name for the seeds \ in QQ15 (which now contains the seeds for the current \ system) .ee1 LDA #0 \ Now to plot the star, so set the high bytes of K, K3 STA K3+1 \ and K4 to 0 STA K4+1 STA K+1 LDA XX12 \ Set the low byte of K3 to XX12, the pixel x-coordinate STA K3 \ of this system LDA QQ15+5 \ Fetch w2_hi for this system from QQ15+5, extract bit 0 AND #1 \ and add 2 to get the size of the star, which we store ADC #2 \ in K. This will be either 2, 3 or 4, depending on the STA K \ value of bit 0, and whether the C flag is set (which \ will vary depending on what happens in the above call \ to cpl). Incidentally, the planet's average radius \ also uses w2_hi, bits 0-3 to be precise, but that \ doesn't mean the two sizes affect each other \ We now have the following: \ \ K(1 0) = radius of star (2, 3 or 4) \ \ K3(1 0) = pixel x-coordinate of system \ \ K4(1 0) = pixel y-coordinate of system \ \ which we can now pass to the SUN routine to draw a \ small "sun" on the Short-range Chart for this system JSR FLFLLS \ Call FLFLLS to reset the LSO block JSR SUN \ Call SUN to plot a sun with radius K at pixel \ coordinate (K3, K4) JSR FLFLLS \ Call FLFLLS to reset the LSO block .TT187 JSR TT20 \ We want to move on to the next system, so call TT20 \ to twist the three 16-bit seeds in QQ15 INC XX20 \ Increment the counter BEQ TT111-1 \ If X = 0 then we have done all 256 systems, so return \ from the subroutine (as TT111-1 contains an RTS) JMP TT182 \ Otherwise jump back up to TT182 to process the next \ system }