Routines
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F78E: Make a character find ERIC
Used by command lists 0xD0, 0xD2, 0xD6, 0xDA and 0xDE to make little boy no. 10, MR WACKER or MR ROCKITT track down ERIC (to deliver a message).
Input
H Character number (0xA1, 0xA3, 0xA4)
F78E LD A,\$FF Adjust the length of the lesson to allow the character enough time to find ERIC
F790 CALL \$FA04
This routine places F79E into bytes 0x6F and 0x70 of the character's buffer, but also uses byte 0x69 (which normally holds the LSB of a routine address) for coordination. When byte 0x69 holds 0xA0 (the LSB of the routine at 7BA0), ERIC's coordinates are compared with those of the character looking for him, and the decision is made whether to keep moving. If the character does need to keep moving, 7BDF is called, which either (a) turns the character round, or (b) puts the character midstride, and places 0xFB (the LSB of the routine at 7BFB) into byte 0x69. When byte 0x69 holds 0xFB, this routine jumps to 7BFB to move the character from the midstride position, and set byte 0x69 back to 0xA0.
F793 LD L,\$69 Initialise byte 0x69 to 0xA0, so on this first pass we compare ERIC's location with that of his chaser
F795 LD (HL),\$A0
F797 LD L,\$6F Place F79E into bytes 0x6F and 0x70 of the character's buffer (thus setting the character's uninterruptible subcommand)
F799 LD (HL),\$9E
F79B INC L
F79C LD (HL),\$F7
Subsequent calls to this routine will enter at this point, by virtue of its address being placed into bytes 0x6F and 0x70 of the character's buffer.
F79E LD A,H A=number of the character looking for ERIC
F79F CP \$A3 Is MR WACKER looking for ERIC?
F7A1 CALL Z,\$7DEA If so, make him walk fast
F7A4 LD L,\$69 Is the character midstride?
F7A6 LD A,(HL)
F7A7 CP \$FB
F7A9 JP Z,\$7BFB Finish the stride if so
The character looking for ERIC is not midstride at the moment. Decide which way (if any) he should go to find ERIC.
F7AC CALL \$79FD Get ERIC's coordinates in DE
F7AF LD L,\$61 Byte 0x61 of the character's buffer holds his y-coordinate
F7B1 LD A,(HL) Pick this up in A
F7B2 CP D Set the zero flag if ERIC is on same floor
F7B3 CALL \$F9E5 Compare this character's coordinates with ERIC's
F7B6 JR NZ,\$F7D4 Jump if this character is on a staircase or more than 3 y-coordinates away from ERIC
F7B8 INC L L=0x62
F7B9 LD A,(HL) A=character's x-coordinate
F7BA SUB E Does it match ERIC's x-coordinate?
F7BB JR NZ,\$F7CC Jump if not
The character looking for ERIC is within 3 x-coordinates and 3 y-coordinates of ERIC's location, and is not on a staircase. In other words, ERIC has been found.
F7BD LD A,(\$7FFB) Check ERIC's status flags at 7FFB, and return if ERIC is firing, hitting, jumping, being spoken to by a little boy, knocked out, or writing on a blackboard
F7C0 AND \$7F
F7C2 RET NZ
F7C3 LD L,\$70 Remove the address of the entry point at F79E from bytes 0x6F and 0x70 of the character's buffer
F7C5 LD (HL),A
F7C6 LD L,\$6A Remove any interruptible subcommand routine address from bytes 0x69 and 0x6A of the character's buffer
F7C8 LD (HL),A
F7C9 JP \$62A8 Move to the next command in the command list
The character looking for ERIC is within 3 y-coordinates of ERIC's location, but not at the same x-coordinate. Is he close enough, though?
F7CC JR NC,\$F7D0 Jump if the character is to the right of ERIC
F7CE NEG Get the absolute x-coordinate distance between the character and ERIC
F7D0 CP \$04 Is ERIC less than 4 x-coordinates away?
F7D2 JR C,\$F7BD Jump if so (that's close enough)
The character has not yet found ERIC.
F7D4 CALL \$7ADC Determine this character's next move
F7D7 JP \$7BDF Set him off in the appropriate direction
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