Routines
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56441: Slow Player Down
Slows the player down when no control is used to move. The distance to the next position that is a multiple of eight units is found, and the speed is the distance (up to four units).
Input
IX Player
Heading zero.
SlowPlayerDown 56441 LD A,(IX+3) Fetch the Y position of the player (moving up the screen).
Find the distance to the next multiple of eight.
SlowPlayerDown_Distance 56444 AND %00000111 Keep the lowest three bits.
56446 JR Z,SlowPlayerDown_Stop Jump to SlowPlayerDown_Stop if the position is a multiple of eight.
56448 NEG Work out the distance to the next multiple of eight units.
56450 ADD A,8
56452 LD C,4 Set a speed of four.
56454 CP C Jump to SlowPlayerDown_Speed if the distance is four or more.
56455 JR NC,SlowPlayerDown_Speed
Halve the greatest speed, and jump to SlowPlayerDown_Speed if the distance is two or more.
56457 SRL C Halve the speed.
56459 CP C Jump to SlowPlayerDown_Speed if the distance is two or more.
56460 JR NC,SlowPlayerDown_Speed
56462 LD C,A Use the distance.
Move the player at this speed.
SlowPlayerDown_Speed 56463 LD A,C Set the speed and move the player.
56464 JR MovePlayer_Speed
Heading one.
SlowPlayerDown_Right 56466 LD A,(IX+1) Fetch the X position of the player (moving right).
56469 JR SlowPlayerDown_Distance Jump to SlowPlayerDown_Distance.
Heading two.
SlowPlayerDown_Down 56471 LD A,(IX+3) Fetch the Y position of the player (moving down the screen).
Heading two or three.
SlowPlayerDown_Negate 56474 NEG Make it negative.
56476 JR SlowPlayerDown_Distance Jump to SlowPlayerDown_Distance.
Heading three.
SlowPlayerDown_Left 56478 LD A,(IX+1) Fetch the X position of the player (moving left).
56481 JR SlowPlayerDown_Negate Jump to SlowPlayerDown_Negate.
The player is at a multiple of eight, so the player stops.
SlowPlayerDown_Stop 56483 LD (IX+5),0 Set the speed of the player to zero and return.
56487 RET
View the equivalent code in;
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