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Routines |
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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 | ||||
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' | ||||
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 | ||||
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 | |||||
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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