Routines
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7BD0: Calculate exterior item isometric position
Calculate isometric screen position for exterior item.
Used by the routine at item_discovered.
Input
HL Pointer to itemstruct's pos.height field.
Set C to ($40 + y - x) * 2
calc_exterior_item_iso_pos 7BD0 DEC HL Step HL back to itemstruct.pos.y
7BD1 LD A,$40 Start with $40
7BD3 ADD A,(HL) Add pos.y
7BD4 DEC HL Subtract pos.x
7BD5 SUB (HL)
7BD6 ADD A,A Double the result
7BD7 LD C,A Save it in C
Set B to ($200 - x - y - height)
7BD8 XOR A Zero the result; this acts like $200 for our purposes
7BD9 SUB (HL) Subtract pos.x
7BDA INC HL Subtract pos.y
7BDB SUB (HL)
7BDC INC HL Subtract pos.height
7BDD SUB (HL)
7BDE LD B,A Save it in B
Write the result to itemstruct.iso_pos
7BDF INC HL Point HL at itemstruct.iso_pos
7BE0 LD (HL),C Store BC
7BE1 INC HL
7BE2 LD (HL),B
7BE3 RET Return
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