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Routines |
| Prev: 26378 | Up: Map | Next: 26453 |
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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 0,(HL) | Set the appropriate bit in the SRB byte for the leftmost character square that needs refreshing; this instruction is modified earlier in this routine to set the required bit | ||||||||
| 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 0,(HL) | Set the appropriate bit in the SRB byte for the rightmost character square that needs refreshing; this instruction is modified immediately before execution to set the required bit | ||||||||
| 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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