Routines
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9B0D: Choose Position
Used by the routine at StartNastie.
Chooses a random position for an actor which is about to appear in the player's room, both the X and Y coordinates are between 30 and AF. The position is rejected if the actor would overlap the player (see TestPlayerTouchingActor) or an object in the room (see SlideActorPastObjects).
Input
IX Actor record
Output
DE The Y and X position (D and E)
F Carry flag set if the position is unsuitable
Use a random X position.
ChoosePosition 9B0D LD A,($9695) Fetch the random seed from RandomNumber.
9B10 AND %01111111 Keep only bits 0-6.
9B12 ADD A,$30 Add 30.
9B14 LD E,A Copy the X position to E.
See Less Enemies.
9B15 LD (IX+$03),A Set the X position of the actor.
This entry point is used by the routine at PlaceFlame.
Use a Y position based on the frame counter.
ChoosePosition_SetY 9B18 LD A,($5C78) Fetch the frame counter from FRAMES.
9B1B AND %01111111 Keep only bits 0-6.
9B1D ADD A,$30 Add 30.
9B1F LD D,A Copy the Y position to D.
9B20 LD (IX+$04),A Set the Y position of the actor.
This entry point is used by the routine at PlaceFlame_InRow.
Put the actor in the player's room and test the position.
ChoosePosition_Test 9B23 LD A,($9703) Fetch the player's room from 9703.
9B26 LD (IX+$01),A Set the room of the actor to the player's room.
9B29 LD BC,$1717 Set the height and width of the actor in B and C to 17.
9B2C CALL TestPlayerTouchingActor Check whether the actor overlaps the player.
9B2F RET C Return if the actor would overlap the player.
9B30 LD BC,$1717 Set the height and width of the actor in B and C to 17.
9B33 CALL SlideActorPastObjects Check whether the actor overlaps an object in the room.
9B36 RET Return.
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