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Routines |
| Prev: 24832 | Up: Map | Next: 24963 |
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| 24843 | LD A,E | A=skool x-coordinate (0-95) | ||||||||
| 24844 | AND 96 | Now H is 128 if 0<=E<32; 136 if 32<=E<64; or 144 if 64<=E<96 | ||||||||
| 24846 | RRCA | |||||||||
| 24847 | INC A | |||||||||
| 24848 | RRCA | |||||||||
| 24849 | LD H,A | |||||||||
| 24850 | LD A,(DE) | A=skool UDG reference for the character square at (E,D) | ||||||||
| 24851 | PUSH DE | |||||||||
| 24852 | LD L,A | HL=base address of the UDG bytes for the character square at (E,D) | ||||||||
| 24853 | LD BC,2048 | B=8, C=0 | ||||||||
| 24856 | LD DE,32513 | Copy the 8 bytes of the skool UDG into the back buffer at 32513 | ||||||||
| 24859 | LD A,(HL) | |||||||||
| 24860 | LD (DE),A | |||||||||
| 24861 | INC H | |||||||||
| 24862 | INC E | |||||||||
| 24863 | DJNZ 24859 | |||||||||
| 24865 | NOP | |||||||||
| 24866 | POP DE | Restore the skool coordinates to DE | ||||||||
| 24867 | LD B,21 | There are 21 characters to consider | ||||||||
| 24869 | LD H,152 | 152=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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| 24871 | LD L,98 | Byte 98 of the character's buffer holds his x-coordinate | ||||||||
| 24873 | LD A,E | A=skool x-coordinate (0-95) | ||||||||
| 24874 | SUB (HL) | Subtract the character's x-coordinate | ||||||||
| 24875 | DEC HL | Byte 97 of the character's buffer holds his y-coordinate | ||||||||
| 24876 | JR C,24926 | Jump if no part of the character's sprite appears at this x-coordinate | ||||||||
| 24878 | CP 3 | |||||||||
| 24880 | JR NC,24926 | |||||||||
| 24882 | 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 | ||||||||
| 24883 | ADD A,A | |||||||||
| 24884 | LD C,A | |||||||||
| 24885 | LD A,D | A=skool y-coordinate (152-172) | ||||||||
| 24886 | SUB (HL) | Subtract the character's y-coordinate | ||||||||
| 24887 | JR C,24926 | Jump if no part of the character's sprite appears at this y-coordinate | ||||||||
| 24889 | CP 4 | |||||||||
| 24891 | JR NC,24926 | |||||||||
| 24893 | ADD A,C | A=0-11, corresponding to the sprite tile that appears at (E,D) | ||||||||
| 24894 | EXX | |||||||||
| 24895 | ADD A,173 | |||||||||
| 24897 | LD H,A | H'=173-184 | ||||||||
| 24898 | EXX | |||||||||
| 24899 | LD L,96 | Pick up the character's animatory state in A | ||||||||
| 24901 | LD A,(HL) | |||||||||
| 24902 | EXX | |||||||||
| 24903 | LD L,A | L'=character's animatory state | ||||||||
| 24904 | LD A,(HL) | A=sprite tile UDG reference | ||||||||
| 24905 | AND A | Is it the blank UDG? | ||||||||
| 24906 | JR Z,24925 | Jump if so | ||||||||
| 24908 | CALL 27914 | 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 32513 (which was originally populated with the relevant skool UDG).
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| 24911 | LD B,8 | There are 8 bytes in the UDG | ||||||||
| 24913 | LD DE,32513 | |||||||||
| 24916 | LD A,(DE) | A=back buffer UDG byte | ||||||||
| 24917 | OR (HL) | OR in the sprite tile UDG byte | ||||||||
| 24918 | INC H | |||||||||
| 24919 | AND (HL) | AND in the sprite tile UDG mask | ||||||||
| 24920 | INC H | |||||||||
| 24921 | LD (DE),A | |||||||||
| 24922 | INC E | |||||||||
| 24923 | DJNZ 24916 | Jump back until the UDG is done | ||||||||
| 24925 | EXX | |||||||||
| 24926 | INC H | Next character | ||||||||
| 24927 | DJNZ 24871 | 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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| 24929 | LD HL,32512 | 32512 holds the leftmost column of the skool on-screen (0-64) | ||||||||
| 24932 | LD A,D | A=skool y-coordinate (152-172) | ||||||||
| 24933 | AND 7 | Set C to the LSB of the display file address corresponding to the screen coordinates (0,D-152) | ||||||||
| 24935 | RRCA | |||||||||
| 24936 | RRCA | |||||||||
| 24937 | RRCA | |||||||||
| 24938 | LD C,A | |||||||||
| 24939 | LD A,E | A=screen x-coordinate (0-31) | ||||||||
| 24940 | SUB (HL) | |||||||||
| 24941 | ADD A,C | Set L to the LSB of the display file address corresponding to the skool coordinates (E,D) | ||||||||
| 24942 | LD L,A | |||||||||
| 24943 | LD A,D | A=screen y-coordinate (0-20) | ||||||||
| 24944 | SUB 152 | |||||||||
| 24946 | AND 24 | Set H to the MSB of the display file address corresponding to the skool coordinates (E,D) | ||||||||
| 24948 | ADD A,64 | |||||||||
| 24950 | 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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| 24951 | LD B,8 | Copy the tile to the screen | ||||||||
| 24953 | LD DE,32513 | |||||||||
| 24956 | LD A,(DE) | |||||||||
| 24957 | LD (HL),A | |||||||||
| 24958 | INC H | |||||||||
| 24959 | INC E | |||||||||
| 24960 | DJNZ 24956 | |||||||||
| 24962 | RET | |||||||||
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