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Routines |
Prev: 27008 | Up: Map |
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 | There are 84 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 | ||||||
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 | |||||
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 | ||||||
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 all 84 bytes in the SRB have been checked | |||||
27081 | RET |
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