Routines
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62368: Update the SRB for a window
Used by the routines at 62468 and 62597. Updates the screen refresh buffer (SRB) for a window (or window-pair) after a light switch has been flipped or a blind has been raised or lowered.
Input
H 185-189 (corresponding to the 5th, 4th, 3rd, 2nd or 1st floor)
L 0-31 or 64-95 (corresponding to the x-coordinate of the window)
62368 RES 6,L Now L=X'/8 (where X' is the x-coordinate of the left edge of the window), and HL points at the Z value corresponding to the window
62370 LD BC,(32766) The play area coordinates of the top-left corner of the screen are stored at 32766 and 32767
62374 LD A,C A=X (the x-coordinate of the leftmost column of the play area on screen)
62375 RRCA A=X/8
62376 RRCA
62377 RRCA
62378 LD E,A E=X/8 (0-31)
62379 LD A,L A=X'/8 (0-31)
62380 SUB E A=X'/8-X/8
62381 CP 4 Is the window off screen to the right or left?
62383 RET NC Return if so
62384 LD E,A E=0-3 (index of the 8-tile wide column containing the window)
62385 LD A,H A=1 (5th floor), 2, 3, 4 or 5 (1st floor)
62386 SUB 184
62388 LD D,A D=6 (5th floor), 12, 18, 24 or 30 (1st floor)
62392 LD D,A
62393 SUB B Subtract Y, the y-coordinate of the topmost row of the play area on screen (2, 8, 14 or 20)
62394 ADD A,4 Is the window off screen?
62396 CP 21
62398 RET NC Return if so
62399 ADD A,A A=4*(D-Y+4)+E
62402 LD E,A Point DE at the SRB byte corresponding to the top row of the window
62403 LD D,127
62405 LD C,128 C=128 (10000000)
62407 LD A,(HL) Pick up the Z value for the window
62408 LD L,A Point HL at the Z'' value for the leftmost column of tiles in the 8-tile wide segment that contains the window
62409 SET 7,L
62411 LD H,184
62413 EXX
62414 LD L,A Point HL' at the Z' value for the 8x6 block of tiles that contains the window
62415 LD H,191
62417 LD C,1 C'=1 (00000001)
62419 EXX
The following loop examines the 8x6 block of tiles that contains the window and updates the relevant SRB bytes for the affected window tiles.
62420 EXX
62421 RRC C Rotate the set bit in C' one place to the right
62423 LD A,(HL) A=Z' value
62424 AND C Set the zero flag if we should use the T values in pages 160, 162, 164, 166, 168 and 170
62425 EXX
62426 PUSH HL Save the pointer to the Z'' value
62427 LD L,(HL) L=Z'' value
62428 LD H,160 Point HL at the T value in page 160
62430 JR Z,62434 Jump unless we should use the T values in pages 172, 174, 176, 178, 180 and 182
62432 LD H,172 Point HL at the T value in page 172
62434 LD B,6 There are 6 rows of tiles to consider
62436 LD A,(HL) A=T
62437 AND 192 Keep only bits 6 and 7
62439 CP 128 Is there a window tile here?
62441 JR NZ,62446 Jump if not
62443 LD A,(DE) Set the appropriate bit in the SRB byte
62444 OR C
62445 LD (DE),A
62446 INC H Point HL at the next T value (in page 162, 164, 166, 168, 170, 174, 176, 178, 180 or 182)
62447 INC H
62448 LD A,E Point DE at the SRB byte for the next row down