Routines
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45604: Handle Block Moving East West
The handler for a block which moves east and west (object 66), and the code shared with HandleBlockMovingNorthSouth. The block follows a target that swings over 32 frames from FrameCounter. Neighbouring blocks are out of step because the low byte of the object address is added in. It moves by 1 each frame, with gravity cancelled out.
The axis is chosen by changing the operands of HandleBlockMoving_Compare and HandleBlockMoving_SetSpeed.
Input
IX The address of the object
Choose the x axis.
HandleBlockMovingEastWest 45604 CALL PlaySoundFromXPosition Call PlaySoundFromXPosition.
45607 LD HL,265 Set HL to 265.
This entry point is used by the routine at HandleBlockMovingNorthSouth.
Change the later instructions to use the chosen axis.
HandleBlockMoving 45610 LD A,H Write H to 45643.
45611 LD (45643),A
45614 LD A,L Write L to 45660.
45615 LD (45660),A
45618 CALL SetPixelAdjustments Call SetPixelAdjustments.
Work out a target from 0 to 15.
45621 PUSH IX Copy IX to BC (using the stack).
45623 POP BC
45624 LD A,C Fetch the low byte and move bit 5 to bit 4.
45625 RRCA
45626 AND %00010000 Keep bit 4.
45628 LD C,A Keep it in C.
45629 LD A,(23298) Fetch FrameCounter.
45632 ADD A,C Add the difference between neighbouring objects.
45633 BIT 4,A Jump to HandleBlockMoving_Target if bit 4 is clear.
45635 JR Z,HandleBlockMoving_Target
45637 CPL Invert it.
HandleBlockMoving_Target 45638 AND %00001111 Keep bits 0 to 3.
45640 LD C,A Keep the target in C.
Set a speed of 1 towards the target.
HandleBlockMoving_Compare 45641 LD A,(IX+1) Fetch the position along the chosen axis.
45644 ADD A,8 Add 8.
45646 AND %00001111 Keep bits 0 to 3.
45648 CP C Jump to SetWipeAndDrawFlags if the block is at the target.
45649 JP Z,SetWipeAndDrawFlags
45652 LD A,1 Set the speed to 1.
45654 JR C,HandleBlockMoving_SetSpeed Jump to HandleBlockMoving_SetSpeed if the block is below the target.
45656 NEG Make the speed negative.
Set that speed, cancel gravity, and move the block.
HandleBlockMoving_SetSpeed 45658 LD (IX+9),A Set the speed along the chosen axis.
45661 LD (IX+11),1 Write 1 as the speed along the z axis.
45665 CALL ApplyGravityAndMove Call ApplyGravityAndMove.
45668 JP SetWipeAndDrawFlags Jump to SetWipeAndDrawFlags.
View the equivalent code in;
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