Routines
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D3A9: Find Path At Position
Used by the routine at TestGroupObjects.
Looks through the entries of the level data, which are found just before the level header at LevelHeaderAddress, for one whose position matches the position of the entity. If one is found the entity is set to follow it by setting fields 24 and 25.
Input
IX The entity
The list is walked backwards from just before the level header. Each entry is a pointer to four position bytes. A match stores the index in field 24 and 48 in field 25.
FindPathAtPosition D3A9 LD HL,($5CFE) The path list sits just before the level header.
D3AC DEC HL
D3AD DEC HL
D3AE DEC HL
D3AF LD C,$41 The first index is 41.
FindPathAtPosition_Loop D3B1 PUSH HL Remember this point in the list.
D3B2 LD E,(HL) Read the pointer to the entry's position.
D3B3 INC HL
D3B4 LD D,(HL)
D3B5 PUSH DE Use that position.
D3B6 POP IY
D3B8 LD A,(IX+$02) The high byte of x has to match.
D3BB CP (IY+$00)
D3BE JR NZ,FindPathAtPosition_Next
D3C0 LD A,(IX+$03) Read the low byte of x.
D3C3 AND %11110000 Use its high nibble.
D3C5 CP (IY+$01) That nibble has to match the entry.
D3C8 JR NZ,FindPathAtPosition_Next
D3CA LD A,(IX+$05) The high byte of y has to match.
D3CD CP (IY+$02)
D3D0 JR NZ,FindPathAtPosition_Next
D3D2 LD A,(IX+$06) Read the low byte of y.
D3D5 AND %11110000 Use its high nibble.
D3D7 CP (IY+$03) That nibble has to match the entry.
D3DA JR NZ,FindPathAtPosition_Next
D3DC LD (IX+$24),C The index becomes field 24.
D3DF LD (IX+$25),$48 Field 25 becomes 48.
D3E3 POP HL Restore the list and return.
D3E4 RET
FindPathAtPosition_Next D3E5 POP HL Step back to the previous entry and take the next index.
D3E6 DEC HL
D3E7 DEC HL
D3E8 INC C
D3E9 JR FindPathAtPosition_Loop Try that entry.
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