Routines
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A498: Test Cell In Direction
Used by the routine at ChooseDirection.
Finds the type of the cell next to an entity in a direction, and tests whether a program packet could go there. The directions are 00 for the lower X cell, 01 for the higher Y cell, 02 for the higher X cell and 03 for the lower Y cell.
Input
A Direction
F The zero flag is set if the direction is zero
DE X position
HL Y position
Output
IY Address of the cell
F The zero flag is set if the packet could go to the cell
A The type of the cell
TestCellInDirection A498 LD C,A Keep the direction.
A499 PUSH DE Save the position.
A49A PUSH HL
A49B JR Z,TestCellInDirection_X1 Jump if the direction is zero.
A49D DEC A Jump if the direction is one.
A49E JR Z,TestCellInDirection_Y1
A4A0 DEC A Jump if the direction is two.
A4A1 JR Z,TestCellInDirection_X2
A4A3 DEC H Otherwise use the lower Y cell.
TestCellInDirection_Cell A4A4 CALL FindMapCell Find the cell using FindMapCell.
A4A7 PUSH HL Copy its address into IY.
A4A8 POP IY
A4AA POP HL Restore the position.
A4AB POP DE
A4AC AND A Return with the zero flag set if the cell is empty (type 00).
A4AD RET Z
A4AE CP $0F Return with the zero flag set if the type is 0F.
A4B0 RET Z
A4B1 CP $01 Return with the zero flag set if the type is 01.
A4B3 RET Z
A4B4 CP $07 Return with the zero flag set if the type is 07.
A4B6 RET Z
A4B7 CP $09 Compare the type with 09, and return.
A4B9 RET
TestCellInDirection_X1 A4BA DEC D Use the lower X cell, and jump back.
A4BB JR TestCellInDirection_Cell
TestCellInDirection_Y1 A4BD INC H Use the higher Y cell, and jump back.
A4BE JR TestCellInDirection_Cell
TestCellInDirection_X2 A4C0 INC D Use the higher X cell, and jump back.
A4C1 JR TestCellInDirection_Cell
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