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Routines |
Prev: 26378 | Up: Map | Next: 26453 |
Used by the routines at 26513 and 26639. Updates the screen refresh buffer (SRB) so that the character squares at (E,D) and (E+1,D) are marked dirty. Two character squares in a row are marked dirty to ensure that blackboard contents are properly displayed (characters written on a blackboard may cross character square boundaries).
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26380 | LD A,(32767) | A=leftmost column of the play area on screen | ||||
26383 | SUB 2 | |||||
26385 | JR C,26389 | Jump if the far left wall of the boys' skool is on-screen | ||||
26387 | CP E | Is the leftmost point requiring refresh off-screen to the left by at least two character squares? | ||||
26388 | RET NC | Return if so (nothing to do) | ||||
26389 | ADD A,33 | A=column of the play area at the far right of the screen | ||||
26391 | CP E | Is the leftmost point requiring refresh off-screen to the right? | ||||
26392 | RET C | Return if so (nothing to do) | ||||
26393 | PUSH DE | Save the coordinates for now | ||||
26394 | SUB 32 | A=screen x-coordinate corresponding to the play area x-coordinate in E (-1, 0-31) | ||||
26396 | CPL | |||||
26397 | ADD A,E | |||||
26398 | BIT 7,A | Is the leftmost point requiring refresh on-screen? | ||||
26400 | JR Z,26403 | Jump if so | ||||
26402 | INC A | A=0 | ||||
26403 | RLCA | A=8x (x=column of the screen containing the first character square to be refreshed) | ||||
26404 | RLCA | |||||
26405 | RLCA | |||||
26406 | LD E,A | Store this in E temporarily | ||||
26407 | AND 56 | Set the instruction at 26428 below to SET n,(HL) where n is the appropriate bit in the SRB byte | ||||
26409 | CPL | |||||
26410 | DEC A | |||||
26411 | LD (26429),A | |||||
26414 | PUSH AF | |||||
26415 | LD A,E | A=8x again | ||||
26416 | RLCA | Point HL at the appropriate byte of the SRB | ||||
26417 | RLCA | |||||
26418 | AND 3 | |||||
26420 | ADD A,D | |||||
26421 | ADD A,D | |||||
26422 | ADD A,D | |||||
26423 | ADD A,D | |||||
26424 | LD E,A | |||||
26425 | LD D,127 | |||||
26427 | EX DE,HL | |||||
26428 | SET n,(HL) | Set the appropriate bit in the SRB byte for the leftmost character square that needs refreshing | ||||
26430 | POP AF | |||||
26431 | ADD A,56 | |||||
26433 | JR C,26443 | Jump unless we've just set bit 0 of an SRB byte | ||||
26435 | INC L | Next SRB byte | ||||
26436 | LD A,L | Does this SRB byte correspond to the first byte of the next row of the screen? | ||||
26437 | AND 3 | |||||
26439 | JR Z,26450 | If so, skip it | ||||
26441 | LD A,254 | Otherwise set bit 7 in this SRB byte | ||||
26443 | OR 192 | |||||
26445 | LD (26449),A | Set the instruction at 26448 below to SET m,(HL) where m is the appropriate bit in the SRB byte | ||||
26448 | SET m,(HL) | Set the appropriate bit in the SRB byte for the rightmost character square that needs refreshing | ||||
26450 | EX DE,HL | Restore the original contents of HL | ||||
26451 | POP DE | Restore the play area coordinates to DE | ||||
26452 | RET |
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