Routines
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45775: Move Creature Horizontally
Used by the routines at Handle_Flying_Creature, Handle_Jellyfish and Handle_Gargoyle.
Moves a creature one step closer to Sabreman's room when it is in a different room x. It does not draw the creature. It is entered with the carry flag set if Sabreman's room x is less than the room x of the creature.
The creature is flagged so that it will be drawn without being erased when it arrives. It accelerates by two on each call in the direction of Sabreman's room, up to a speed of 48 and its x position changes by a sixteenth of the speed. When the x position goes past 208 (or below 24) it moves into the next room.
The y position is kept at 64 or more, and when it is 128 or more it moves up two pixels each time.
A creature cannot leave its room through a wall. If the wall is on the side that it is going to, it is removed when it is in the same room y as Sabreman, and otherwise Move_Creature_Vertically moves it up or down.
Input
IX Object record
E Flags of the room that the creature is in
Move_Creature_Horizontally 45775 LD (IX+15),1 Set the redraw flags to 1 so that the creature is drawn without being erased when it arrives.
45779 LD (IX+11),0 Clear the contact flags.
45783 JR C,Move_Creature_Horizontally_Move_Left Jump to Move_Creature_Horizontally_Move_Left if Sabreman is on the left of the creature.
45785 BIT 2,E Jump to Move_Creature_Horizontally_Blocked if the room has a right wall.
45787 JR NZ,Move_Creature_Horizontally_Blocked
45789 LD A,(IX+8) Fetch the x velocity.
45792 ADD A,2 Accelerate to the right by adding two.
45794 BIT 7,A Jump to Move_Creature_Horizontally_Store_Velocity if the x velocity is negative.
45796 JR NZ,Move_Creature_Horizontally_Store_Velocity
45798 CP 49 Jump to Move_Creature_Horizontally_Move_Right if the x velocity has reached 49.
45800 JR NC,Move_Creature_Horizontally_Move_Right
Move_Creature_Horizontally_Store_Velocity 45802 LD (IX+8),A Store the x velocity.
Move_Creature_Horizontally_Move_Right 45805 LD A,(IX+8) Fetch the x velocity.
45808 SRA A Divide it by sixteen, keeping the sign.
45810 SRA A
45812 SRA A
45814 SRA A
45816 ADD A,(IX+1) Add the x position of the creature.
45819 CP 208 Jump to Move_Creature_Horizontally_Store_X if the x position is less than 208.
45821 JR C,Move_Creature_Horizontally_Store_X
45823 INC (IX+2) Move the creature to the room on the right.
45826 LD A,8 Set the x position to 8.
Move_Creature_Horizontally_Store_X 45828 LD (IX+1),A Store the x position.
Keep the y position between 64 and 128 and make it drift upwards when it is 128 or more.
Move_Creature_Horizontally_Adjust_Y 45831 LD A,(IX+3) Fetch the y position.
45834 CP 64 Jump to Move_Creature_Horizontally_Drift_Up if the y position is 64 or more.
45836 JR NC,Move_Creature_Horizontally_Drift_Up
45838 LD (IX+3),64 Set the y position to 64.
Move_Creature_Horizontally_Drift_Up 45842 CP 128 Return if the y position is less than 128.
45844 RET C
45845 SUB 2 Subtract two.
45847 LD (IX+3),A Store the y position.
45850 RET Return.
Sabreman is on the left of the creature.
Move_Creature_Horizontally_Move_Left 45851 BIT 6,E Jump to Move_Creature_Horizontally_Blocked if the room has a left wall.
45853 JR NZ,Move_Creature_Horizontally_Blocked
45855 LD A,(IX+8) Fetch the x velocity.
45858 SUB 2 Accelerate to the left by subtracting two.
45860 BIT 7,A Jump to Move_Creature_Horizontally_Store_Left_Velocity if the x velocity is positive.
45862 JR Z,Move_Creature_Horizontally_Store_Left_Velocity
45864 CP 208 Jump to Move_Creature_Horizontally_Add_Left_Velocity if the x velocity is less than 208.
45866 JR C,Move_Creature_Horizontally_Add_Left_Velocity
Move_Creature_Horizontally_Store_Left_Velocity 45868 LD (IX+8),A Store the x velocity.
Move_Creature_Horizontally_Add_Left_Velocity 45871 LD A,(IX+8) Fetch the x velocity.
45874 SRA A Divide it by sixteen, keeping the sign.
45876 SRA A
45878 SRA A
45880 SRA A
45882 ADD A,(IX+1) Add the x position of the creature.
45885 CP 24 Jump to Move_Creature_Horizontally_Store_Left_X if the x position is 24 or more.
45887 JR NC,Move_Creature_Horizontally_Store_Left_X
45889 DEC (IX+2) Move the creature to the room on the left.
45892 LD A,223 Set the x position to 223.
Move_Creature_Horizontally_Store_Left_X 45894 LD (IX+1),A Store the x position.
45897 JR Move_Creature_Horizontally_Adjust_Y Jump to Move_Creature_Horizontally_Adjust_Y.
The creature cannot go that way.
Move_Creature_Horizontally_Blocked 45899 LD A,(36638) Fetch the room y of Sabreman.
45902 CP (IX+4) Jump to Move_Creature_Vertically if the creature is in a different room y.
45905 JR NZ,Move_Creature_Vertically
This entry point is used by the routine at Move_Creature_Vertically.
Move_Creature_Horizontally_Remove_Creature 45907 LD (IX+0),0 Remove the creature.
45911 RET Return.
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