Martianoids: Routine at AA58

AA58: Move Right

Used by the routines at MoveEntity and MoveRobot.

Moves an entity in direction two, which increases the X position. See MoveEntity for how the move works.

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

Output
A	01 if the entity has been blocked
B	Number of steps that are left
DE	New X position
F	The zero flag is reset if the entity has been blocked

MoveRight

AA58

LD A,B

Return if there are no steps left.

AA59

AND A

AA5A

RET Z

AA5B

LD A,E

Jump if the entity is at the start of a cell.

AA5C

AND A

AA5D

JR Z,MoveRight_CellStart

AA5F

ADD A,B

Add the steps to the fraction, and jump if that goes into the next cell.

AA60

JR C,MoveRight_NextCell

AA62

LD E,A

Store the new fraction.

MoveRight_Finish

AA63

XOR A

Clear the number of steps that are left, and return with the zero flag set.

AA64

LD B,A

AA65

RET

MoveRight_NextCell

AA66

LD B,A

Keep the steps that are left over.

AA67

LD A,D

Fetch the X cell...

AA68

INC A

...and add one...

AA69

AND $3F

...making sure that the cell is within the map.

AA6B

LD D,A

AA6C

XOR A

Move to the start of the cell, and return with the zero flag set.

AA6D

LD E,A

AA6E

RET

Return.

MoveRight_CellStart

AA6F

ADD A,B

Add the steps to the fraction...

AA70

LD E,A

...and keep it.

AA71

LD ($9653),DE

Keep this position.

AA75

PUSH DE

Save the X position.

AA76

LD A,D

Fetch the X cell...

AA77

INC A

...and add one...

AA78

AND $3F

...making sure that the cell is within the map.

AA7A

LD D,A

AA7B

CALL FindMapCell

Find the cell using FindMapCell.

AA7E

JR Z,MoveRight_Clear

Jump if the cell is empty.

AA80

PUSH HL

Save the Y position.

AA81

LD HL,($962E)

Fetch the address of the cell...

AA84

LD A,(HL)

...and its contents...

AA85

POP HL

...and restore the Y position.

AA86

AND $0F

Jump if the cell has no type.

AA88

JR Z,MoveRight_Clear

AA8A

CP $0F

Jump if the cell is not type 0F, which is an obstacle.

AA8C

JR NZ,MoveRight_Blocked

MoveRight_Clear

AA8E

POP DE

Restore the X position...

AA8F

JR MoveRight_Finish

...and jump to finish the move.

MoveRight_Blocked

AA91

POP DE

The entity is blocked, so restore the old X position.

AA92

XOR A

Clear the number of steps that are left...

AA93

LD B,A

AA94

LD E,A

...and the fraction...

AA95

INC A

...and set A to 01.

AA96

RET

Return.