Martianoids: Routine at 43459

43459: Move Entity

Used by the routines at TryMove and MoveDestroyer.

Moves an entity in the direction that it is heading, by up to the number of steps that is given. The entity stops at the start of a cell if the next cell is not empty. The routine keeps a copy of the position, so that a move can be undone.

Input
B	Number of steps to take
DE	X position
HL	Y position
IX	Entity

Output
A	1 if the entity has been blocked
B	Number of steps that are left
DE	New X position
HL	New Y position
F	The zero flag is reset if the entity has been blocked

MoveEntity

43459

LD (38483),DE

Keep the X position...

43463

LD (38485),HL

...and the Y position, so that the move can be undone.

43466

LD A,(IX+7)

Fetch the direction of the entity...

43469

AND 3

...and jump to move in direction zero (X decreasing)...

43471

JP Z,MoveLeft

43474

DEC A

...or direction one (Y increasing)...

43475

JP Z,MoveUp

43478

DEC A

...or direction two (X increasing)...

43479

JP Z,MoveRight

43482

JP MoveDown

...or otherwise direction three (Y decreasing).