Through the Trap Door: Routine at 54313

54313: Move entity at IX into room to the right, if appropriate

This routine moves an entity (e.g. Berk or Drutt) into the next room to the right, if there is one, in a way that is consistent with the point of view of the currently selected character. For example, if Berk is the selected character and he moves into a new room, he does so as soon as his leading side (left or right) crosses the edge of the screen. He essentially disappears immediately from his old room. However from Drutt's point of view, Berk should move across the boundary smoothly and not just vanish as soon as his leading side crosses the boundary. This routine (along with its counterpart at 54348) ensures that this happens correctly.

Used by the routines at 36116, 36542, 39278, 41961, 42266, 52148, 52193, 52889, 52914 and 55041.

Input
IX	Address of complex state data for an entity

Output
A	Zero if no room exists to the right, otherwise, x-coordinate of character's appropriate side
F	Carry flag set if entity is not at edge of current room, or has moved into new room and has not collided. Reset otherwise (i.e. can't enter new room).

54313

LD A,(34235)

Load C with width of entity's current room (chars) + 99...

54316

LD C,A

...

54317

LD A,(34208)

If Drutt-mode flag is reset (Berk mode)...

54320

BIT 0,A

...

54322

JR Z,54329

...then skip ahead to 54329

54324

LD A,(IX+5)

Load A with x-coordinate of Drutt's left side

54327

JR 54332

Skip ahead to 54332

54329

LD A,(IX+7)

Load A with x-coordinate of Berk's right side

54332

CP C

If x-coordinate of room's right edge is greater than x-coordinate in A...

54333

RET C

...then return

54334

CALL 54505

Load B with index of room to right of current character's current room

54337

JR Z,54381

If there is no room to the right, then jump to 54381

54339

CALL 54383

Move entity at IX into room to right of its current room and update position of carried entity if moving entity is Berk

54342

CALL 54569

Check entity at IX for collision with another impassable / pushable entity immediately to the right...

54345

JR NC,54381

...and if a collision occurred, then jump to 54381

54347

RET

Return