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Routines |
| Prev: 27008 | Up: Map | Next: 27082 |
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Used by the routines at 25856, 26471, 32470 and 46312. Goes through the screen refresh buffer (SRB) and for every set bit found, updates the corresponding character square on-screen.
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| 27026 | LD HL,32524 | Point HL at the first byte of the SRB | ||
| 27029 | LD B,84 | B will count the bytes in the screen refresh buffer | ||
| 27031 | LD A,(HL) | Pick up an SRB byte | ||
| 27032 | AND A | Any character squares in this segment need refreshing? | ||
| 27033 | JR Z,27078 | Jump if not | ||
| 27035 | PUSH BC | Save the SRB byte counter | ||
| 27036 | LD A,L | D=y-coordinate of the segment of 8 character squares to which this SRB byte corresponds | ||
| 27037 | AND 124 | |||
| 27039 | RRCA | |||
| 27040 | RRCA | |||
| 27041 | ADD A,149 | |||
| 27043 | LD D,A | |||
| 27044 | LD A,L | E=x-coordinate of the leftmost character square in the segment | ||
| 27045 | AND 3 | |||
| 27047 | RLCA | |||
| 27048 | RLCA | |||
| 27049 | RLCA | |||
| 27050 | LD E,A | |||
| 27051 | LD A,(32512) | |||
| 27054 | ADD A,E | |||
| 27055 | LD E,A | |||
| 27056 | DEC E | |||
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Here we enter a loop to check each SRB byte for set bits.
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| 27057 | PUSH HL | Save the pointer to the SRB byte | ||
| 27058 | INC E | Set DE to the coordinates of the next character square in the current segment | ||
| 27059 | RR (HL) | Push an SRB bit into the carry flag, and 0 into bit 7 of the SRB byte | ||
| 27061 | JR C,27067 | Refresh the corresponding character square if the bit was set | ||
| 27063 | JR NZ,27058 | Jump back until all set bits in the SRB byte have been checked | ||
| 27065 | JR 27076 | Move to the next SRB byte | ||
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We have found a set bit in the current SRB byte. Refresh the corresponding tile on screen.
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| 27067 | PUSH DE | |||
| 27068 | CALL 24843 | Print the character square at (E,D) | ||
| 27071 | POP DE | |||
| 27072 | POP HL | Restore the pointer to the SRB byte | ||
| 27073 | AND A | Clear the carry flag so that bit 7 of the SRB byte will be reset, and jump back to check the next bit | ||
| 27074 | JR 27057 | |||
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There are no set bits remaining in the current SRB byte. Move on to the next.
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| 27076 | POP HL | Restore the pointer to the SRB byte | ||
| 27077 | POP BC | Restore the SRB byte counter to B | ||
| 27078 | INC L | Move to the next byte in the screen refresh buffer | ||
| 27079 | DJNZ 27031 | Jump back until every byte in the SRB has been checked | ||
| 27081 | RET | |||
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