Routines
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A5CD: Choose Velocity
Used by the routines at HandlerChooseNastie and HandlerWanderingNastie.
Chooses the velocity for a wandering actor. If it is moving then it is stopped (by StopActor). If it has stopped then it is given a random X velocity and a random Y velocity from VelocityTable, and the sprite is made to face the way it is going.
Input
IX Actor record
ChooseVelocity A5CD LD A,(IX+$06) Fetch the X velocity of the actor.
A5D0 OR (IX+$07) Combine it with the Y velocity.
A5D3 JR NZ,StopActor Jump to StopActor to stop the actor if it is moving.
Choose the X velocity.
A5D5 LD A,($9695) Fetch the random seed from RandomNumber.
A5D8 AND %00000111 Keep only bits 0-2.
A5DA LD L,A Stash the velocity index in L.
A5DB LD H,$00 Clear H.
A5DD LD BC,$A601 Point BC at the table of velocities at VelocityTable.
A5E0 ADD HL,BC Add the table address to get the address of the velocity.
A5E1 LD A,(HL) Fetch the velocity from the table.
A5E2 LD (IX+$06),A Set the X velocity of the actor.
A5E5 BIT 7,A Jump to ChooseVelocity_Right if the actor is moving right.
A5E7 JR Z,ChooseVelocity_Right
A5E9 RES 1,(IX+$00) Reset bit 1 of the sprite ID so that the actor faces left.
Choose the Y velocity.
ChooseVelocity_Y A5ED LD A,($5C78) Fetch the low byte of FRAMES.
A5F0 AND %00000111 Keep only bits 0-2.
A5F2 LD L,A Stash the velocity index in L.
A5F3 LD H,$00 Clear H.
A5F5 ADD HL,BC Add the table address to get the address of the velocity.
A5F6 LD A,(HL) Fetch the velocity from the table.
A5F7 LD (IX+$07),A Set the Y velocity of the actor.
A5FA RET Return.
The actor is moving to the right.
ChooseVelocity_Right A5FB SET 1,(IX+$00) Set bit 1 of the sprite ID so that the actor faces right.
A5FF JR ChooseVelocity_Y Jump to ChooseVelocity_Y to choose the Y velocity.
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