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Routines |
| Prev: 6100 | Up: Map | Next: 6183 |
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| 610B | LD A,E | A=skool x-coordinate (0-95) | ||||||||
| 610C | AND $60 | Now H is 0x80 if 0<=E<32; 0x88 if 32<=E<64; or 0x90 if 64<=E<96 | ||||||||
| 610E | RRCA | |||||||||
| 610F | INC A | |||||||||
| 6110 | RRCA | |||||||||
| 6111 | LD H,A | |||||||||
| 6112 | LD A,(DE) | A=skool UDG reference for the character square at (E,D) | ||||||||
| 6113 | PUSH DE | |||||||||
| 6114 | LD L,A | HL=base address of the UDG bytes for the character square at (E,D) | ||||||||
| 6115 | LD BC,$0800 | B=8, C=0 | ||||||||
| 6118 | LD DE,$7F01 | Copy the 8 bytes of the skool UDG into the back buffer at 7F01 | ||||||||
| 611B | LD A,(HL) | |||||||||
| 611C | LD (DE),A | |||||||||
| 611D | INC H | |||||||||
| 611E | INC E | |||||||||
| 611F | DJNZ $611B | |||||||||
| 6121 | NOP | |||||||||
| 6122 | POP DE | Restore the skool coordinates to DE | ||||||||
| 6123 | LD B,$15 | There are 21 characters to consider | ||||||||
| 6125 | LD H,$98 | 0x98=little boy no. 1 | ||||||||
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Now we enter a loop that checks which part (if any) of each character's sprite appears at the skool coordinates in DE.
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| 6127 | LD L,$62 | Byte 0x62 of the character's buffer holds his x-coordinate | ||||||||
| 6129 | LD A,E | A=skool x-coordinate (0-95) | ||||||||
| 612A | SUB (HL) | Subtract the character's x-coordinate | ||||||||
| 612B | DEC HL | Byte 0x61 of the character's buffer holds his y-coordinate | ||||||||
| 612C | JR C,$615E | Jump if no part of the character's sprite appears at this x-coordinate | ||||||||
| 612E | CP $03 | |||||||||
| 6130 | JR NC,$615E | |||||||||
| 6132 | ADD A,A | Now C is 0, 4 or 8, corresponding to the column (left, middle or right) of the character's sprite that aligns with x-coordinate E | ||||||||
| 6133 | ADD A,A | |||||||||
| 6134 | LD C,A | |||||||||
| 6135 | LD A,D | A=skool y-coordinate (152-172) | ||||||||
| 6136 | SUB (HL) | Subtract the character's y-coordinate | ||||||||
| 6137 | JR C,$615E | Jump if no part of the character's sprite appears at this y-coordinate | ||||||||
| 6139 | CP $04 | |||||||||
| 613B | JR NC,$615E | |||||||||
| 613D | ADD A,C | A=0x00-0x0B, corresponding to the sprite tile that appears at (E,D) | ||||||||
| 613E | EXX | |||||||||
| 613F | ADD A,$AD | |||||||||
| 6141 | LD H,A | H'=0xAD-0xB8 | ||||||||
| 6142 | EXX | |||||||||
| 6143 | LD L,$60 | Pick up the character's animatory state in A | ||||||||
| 6145 | LD A,(HL) | |||||||||
| 6146 | EXX | |||||||||
| 6147 | LD L,A | L'=character's animatory state | ||||||||
| 6148 | LD A,(HL) | A=sprite tile UDG reference | ||||||||
| 6149 | AND A | Is it the blank UDG? | ||||||||
| 614A | JR Z,$615D | Jump if so | ||||||||
| 614C | CALL $6D0A | Get the base address of the sprite tile UDG bytes in HL' | ||||||||
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The following inner loop superimposes the sprite tile onto the tile built up so far in the back buffer at 7F01 (which was originally populated with the relevant skool UDG).
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| 614F | LD B,$08 | There are 8 bytes in the UDG | ||||||||
| 6151 | LD DE,$7F01 | |||||||||
| 6154 | LD A,(DE) | A=back buffer UDG byte | ||||||||
| 6155 | OR (HL) | OR in the sprite tile UDG byte | ||||||||
| 6156 | INC H | |||||||||
| 6157 | AND (HL) | AND in the sprite tile UDG mask | ||||||||
| 6158 | INC H | |||||||||
| 6159 | LD (DE),A | |||||||||
| 615A | INC E | |||||||||
| 615B | DJNZ $6154 | Jump back until the UDG is done | ||||||||
| 615D | EXX | |||||||||
| 615E | INC H | Next character | ||||||||
| 615F | DJNZ $6127 | Jump back to consider the next character | ||||||||
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The display tile (consisting of the skool UDG with all relevant sprite tiles superimposed) has been built. Figure out where in the display file it should be printed.
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| 6161 | LD HL,$7F00 | 7F00 holds the leftmost column of the skool on-screen (0-64) | ||||||||
| 6164 | LD A,D | A=skool y-coordinate (152-172) | ||||||||
| 6165 | AND $07 | Set C to the LSB of the display file address corresponding to the screen coordinates (0,D-152) | ||||||||
| 6167 | RRCA | |||||||||
| 6168 | RRCA | |||||||||
| 6169 | RRCA | |||||||||
| 616A | LD C,A | |||||||||
| 616B | LD A,E | A=screen x-coordinate (0-31) | ||||||||
| 616C | SUB (HL) | |||||||||
| 616D | ADD A,C | Set L to the LSB of the display file address corresponding to the skool coordinates (E,D) | ||||||||
| 616E | LD L,A | |||||||||
| 616F | LD A,D | A=screen y-coordinate (0-20) | ||||||||
| 6170 | SUB $98 | |||||||||
| 6172 | AND $18 | Set H to the MSB of the display file address corresponding to the skool coordinates (E,D) | ||||||||
| 6174 | ADD A,$40 | |||||||||
| 6176 | LD H,A | |||||||||
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Having computed the appropriate display file address in HL, copy the tile from the back buffer to the screen.
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| 6177 | LD B,$08 | Copy the tile to the screen | ||||||||
| 6179 | LD DE,$7F01 | |||||||||
| 617C | LD A,(DE) | |||||||||
| 617D | LD (HL),A | |||||||||
| 617E | INC H | |||||||||
| 617F | INC E | |||||||||
| 6180 | DJNZ $617C | |||||||||
| 6182 | RET | |||||||||
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