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Elite on the BBC Micro

Utility routines: TTX66 (6502SP version)

Name: TTX66 [View in context] Type: Subroutine [Compare versions] Category: Utility routines Summary: Send control code 11 to the I/O processor to clear the top part of the screen and draw a white border
Clear the top part of the screen (the space view) and draw a white border along the top and sides. Other entry points: BOX Just draw the border and (if this is a space view) the view name. This can be used to remove the border and view name, as it is drawn using EOR logic
.TTX66 JSR MT2 \ Switch to Sentence Case when printing extended tokens JSR PBZE \ Reset the pixel buffer size in PBUP JSR HBZE \ Reset the horizontal line buffer size in HBUP STZ LBUP \ Reset the line buffer size at LBUP STZ LSP \ Reset the ball line heap pointer at LSP LDA #%10000000 \ Set bit 7 of QQ17 to switch to Sentence Case STA QQ17 STA DTW2 \ Set bit 7 of DTW2 to indicate we are not currently \ printing a word JSR FLFLLS \ Call FLFLLS to reset the LSO block LDA #YELLOW \ Send a #SETCOL YELLOW command to the I/O processor to JSR DOCOL \ switch to colour 2, which is yellow STZ LAS2 \ Set LAS2 = 0 to stop any laser pulsing STZ DLY \ Set the delay in DLY to 0, to indicate that we are \ no longer showing an in-flight message, so any new \ in-flight messages will be shown instantly STZ de \ Clear de, the flag that appends " DESTROYED" to the \ end of the next text token, so that it doesn't LDA #11 \ Send control code 11 to OSWRCH, to instruct the I/O JSR OSWRCH \ processor to clear the top part of the screen LDX QQ22+1 \ Fetch into X the number that's shown on-screen during \ the hyperspace countdown BEQ OLDBOX \ If the counter is zero then we are not counting down \ to hyperspace, so jump to OLDBOX to skip the next \ instruction JSR ee3 \ Print the 8-bit number in X at text location (0, 1), \ i.e. print the hyperspace countdown in the top-left \ corner .OLDBOX LDA #1 \ Move the text cursor to column 1 JSR DOYC LDA QQ11 \ If this is not a space view, jump to tt66 to skip BNE tt66 \ displaying the view name LDA #11 \ Move the text cursor to row 11 JSR DOXC LDA #CYAN \ Send a #SETCOL CYAN command to the I/O processor to JSR DOCOL \ switch to colour 3, which is cyan in the space view LDA VIEW \ Load the current view into A: \ \ 0 = front \ 1 = rear \ 2 = left \ 3 = right ORA #&60 \ OR with &60 so we get a value of &60 to &63 (96 to 99) JSR TT27 \ Print recursive token 96 to 99, which will be in the \ range "FRONT" to "RIGHT" JSR TT162 \ Print a space LDA #175 \ Print recursive token 15 ("VIEW ") JSR TT27 .tt66 LDA #1 \ Move the text cursor to column 1, row 1 JSR DOXC JSR DOYC LDX #0 \ Set QQ17 = 0 to switch to ALL CAPS STX QQ17 RTS \ Return from the subroutine .BOX LDA #YELLOW \ Send a #SETCOL YELLOW command to the I/O processor to JSR DOCOL \ switch to colour 2, which is yellow LDX #0 \ Set QQ17 = 0 to switch to ALL CAPS STX QQ17 STX X1 \ Set (X1, Y1) to (0, 0) STX Y1 STX Y2 \ Set Y2 = 0 DEX \ Set X2 = 255 STX X2 JSR LL30 \ Draw a line from (X1, Y1) to (X2, Y2), so that's \ (0, 0) to (255, 0), along the very top of the screen LDA #2 \ Set X1 = X2 = 2 STA X1 STA X2 JSR BOS2 \ Call BOS2 below, which will call BOS1 twice, and then \ fall through into BOS2 again, so we effectively do \ BOS1 four times, decrementing X1 and X2 each time \ before calling LOIN, so this whole loop-within-a-loop \ mind-bender ends up drawing these four lines: \ \ (1, 0) to (1, 191) \ (0, 0) to (0, 191) \ (255, 0) to (255, 191) \ (254, 0) to (254, 191) \ \ So that's a 2-pixel wide vertical border along the \ left edge of the upper part of the screen, and a \ 2-pixel wide vertical border along the right edge .BOS2 JSR BOS1 \ Call BOS1 below and then fall through into it, which \ ends up running BOS1 twice. This is all part of the \ loop-the-loop border-drawing mind-bender explained \ above .BOS1 LDA #0 \ Set Y1 = 0 STA Y1 LDA #2*Y-1 \ Set Y2 = 2 * #Y - 1. The constant #Y is 96, the STA Y2 \ y-coordinate of the mid-point of the space view, so \ this sets Y2 to 191, the y-coordinate of the bottom \ pixel row of the space view DEC X1 \ Decrement X1 and X2 DEC X2 JMP LL30 \ Draw a line from (X1, Y1) to (X2, Y2), and return from \ the subroutine using a tail call