.draw_tail JSR tube_get \ Get the parameters from the parasite for the command: STA X1 \ JSR tube_get \ draw_tail(x, y, base_colour, alt_colour, height) STA Y1 \ JSR tube_get \ and store them as follows: STA COL \ JSR tube_get \ * X1 = ship's screen x-coordinate on the scanner STA Y2 \ JSR tube_get \ * Y1 = ship's screen y-coordinate on the scanner STA P \ \ * COL = base colour \ \ * Y2 = alternating (EOR) colour \ \ * P = stick height .SC48 JSR CPIX2 \ Call CPIX2 to draw a single-height dash at (X1, Y1) DEC Y1 \ Decrement the y-coordinate in Y1 so the next call to \ CPIX2 draws another dash on the line above, resulting \ in a double-height dash JSR CPIX2 \ Call CPIX2 to draw a single-height dash at (X1, Y1) \ These calls also leave the following variables set up \ for the dot's top-right pixel, the last pixel to be \ drawn by the second call to CPIX2: \ \ SC(1 0) = screen address of the pixel's character \ block \ \ Y = number of the character row containing the pixel \ \ X = the pixel's number (0-3) in that row \ \ We can use there as the starting point for drawing the \ stick, if there is one LDA CTWOS+1,X \ Load the same mode 5 1-pixel byte that we just used AND COL \ for the top-right pixel, mask it with the base colour STA COL \ in COL, and store the result in COL, so we can use it \ as the character row byte for the base colour stripes \ in the stick LDA CTWOS+1,X \ Load the same mode 5 1-pixel byte that we just used AND Y2 \ for the top-right pixel, mask it with the EOR colour STA Y2 \ in Y2, and store the result in Y2, so we can use it \ as the character row byte for the alternate colour \ stripes in the stick LDX P \ Fetch the stick height from P into X BEQ RTS \ If the stick height is zero, then there is no stick to \ draw, so return from the subroutine (as RTS contains \ an RTS) BMI RTS+1 \ If the stick height in A is negative, jump down to \ RTS+1 .VLL1 \ If we get here then the stick length is positive (so \ the dot is below the ellipse and the stick is above \ the dot, and we need to draw the stick upwards from \ the dot) DEY \ We want to draw the stick upwards, so decrement the \ pixel row in Y BPL VL1 \ If Y is still positive then it correctly points at the \ line above, so jump to VL1 to skip the following LDY #7 \ We just decremented Y up through the top of the \ character block, so we need to move it to the last row \ in the character above, so set Y to 7, the number of \ the last row DEC SC+1 \ Decrement the high byte of the screen address to move \ to the character block above .VL1 LDA COL \ Set A to the character row byte for the stick, which \ we stored in COL above, and which has the same pixel \ pattern as the bottom-right pixel of the dot (so the \ stick comes out of the right side of the dot) EOR Y2 \ Apply the alternating colour in Y2 to the stick STA COL \ Update the value in COL so the alternating colour is \ applied every other row (as doing an EOR twice \ reverses it) EOR (SC),Y \ Draw the stick on row Y of the character block using STA (SC),Y \ EOR logic DEX \ Decrement the (positive) stick height in X BNE VLL1 \ If we still have more stick to draw, jump up to VLL1 \ to draw the next pixel .RTS RTS \ Return from the subroutine \ If we get here then the stick length is negative (so \ the dot is above the ellipse and the stick is below \ the dot, and we need to draw the stick downwards from \ the dot) INY \ We want to draw the stick downwards, so we first \ increment the row counter so that it's pointing to the \ bottom-right pixel in the dot (as opposed to the top- \ right pixel that the call to CPIX4 finished on) CPY #8 \ If the row number in Y is less than 8, then it BNE P%+6 \ correctly points at the next line down, so jump to \ VLL2 to skip the following LDY #0 \ We just incremented Y down through the bottom of the \ character block, so we need to move it to the first \ row in the character below, so set Y to 0, the number \ of the first row INC SC+1 \ Increment the high byte of the screen address to move \ to the character block above .VLL2 INY \ We want to draw the stick itself, heading downwards, \ so increment the pixel row in Y CPY #8 \ If the row number in Y is less than 8, then it BNE VL2 \ correctly points at the next line down, so jump to \ VL2 to skip the following LDY #0 \ We just incremented Y down through the bottom of the \ character block, so we need to move it to the first \ row in the character below, so set Y to 0, the number \ of the first row INC SC+1 \ Increment the high byte of the screen address to move \ to the character block above .VL2 LDA COL \ Set A to the character row byte for the stick, which \ we stored in COL above, and which has the same pixel \ pattern as the bottom-right pixel of the dot (so the \ stick comes out of the right side of the dot) EOR Y2 \ Apply the alternating colour in Y2 to the stick STA COL \ Update the value in COL so the alternating colour is \ applied every other row (as doing an EOR twice \ reverses it) EOR (SC),Y \ Draw the stick on row Y of the character block using STA (SC),Y \ EOR logic INX \ Increment the (negative) stick height in X BNE VLL2 \ If we still have more stick to draw, jump up to VLL2 \ to draw the next pixel RTS \ Return from the subroutineName: draw_tail [Show more] Type: Subroutine Category: Dashboard Summary: Implement the draw_tail command (draw a ship on the 3D scanner)Context: See this subroutine in context in the source code References: This subroutine is called as follows: * tube_table calls draw_tail
This routine is run when the parasite sends a draw_tail command. It draws a ship on the 3D scanner, as a dot and (if applicable) a tail, using the base and alternating colours specified (so it can draw a striped tail for when an I.F.F. system is fitted).
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Subroutine CPIX2 (category: Drawing pixels)
Draw a single-height dash on the dashboard
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Variable CTWOS (category: Drawing pixels)
Ready-made single-pixel character row bytes for mode 5
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Label RTS is local to this routine
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Label VL1 is local to this routine
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Label VL2 is local to this routine
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Label VLL1 is local to this routine
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Label VLL2 is local to this routine
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Subroutine tube_get (category: Tube)
As the I/O processor, fetch a byte that's been sent over the Tube from the parasite