Routines
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C535: Block Movement In Z
Used by the routine at BlockMovement.
Brings the speed along z of an object closer to zero until it does not run into any other object. This works in the same way as BlockMovementInX, except that the object that is hit is flagged as touched (bit 3 of its extra flags) if the player is the object that hit it. An object which can be moved gives its speed along z to the other object, and takes on the speeds along x and y of the other object if it has none of its own.
Input
C Speed along x
L Speed along y
H Speed along z
IX The address of the object
Output
H The new speed along z
Walk the object table.
BlockMovementInZ C535 LD IY,$5B88 Point IY at PlayerBottomObject.
C539 LD B,$38 Set a counter of 38 objects.
Skip unless the object is solid and already overlaps along x and y.
BlockMovementInZ_Next C53B CALL TestObjectSolid Jump to BlockMovementInZ_Advance if the object is not present or is ignored.
C53E JR Z,BlockMovementInZ_Advance
C540 CALL TestOverlapInX Jump to BlockMovementInZ_Advance if the objects do not overlap along x.
C543 JR NC,BlockMovementInZ_Advance
C545 CALL TestOverlapInY Jump to BlockMovementInZ_Advance if the objects do not overlap along y.
C548 JR NC,BlockMovementInZ_Advance
Test whether they overlap along z after the move.
BlockMovementInZ_Test C54A CALL TestOverlapInZ Jump to BlockMovementInZ_Advance if the objects do not overlap along z after the move.
C54D JR NC,BlockMovementInZ_Advance
Flag the object as blocked along z, then apply the kill flags.
C54F SET 2,(IX+$0C) Flag the object as blocked along z.
C553 LD A,(IX+$0D) Fetch the extra flags and move the bit that it kills what it hits into bit 6.
C556 RRCA
C557 AND %01000000 Keep the bit that flags the other object as killed.
C559 OR (IY+$0D) Set it in the extra flags of the other object, if the object kills what it runs into.
C55C LD (IY+$0D),A
C55F RLCA Move the bit that the other object kills what hits it into bit 6.
C560 AND %01000000 Keep the bit that flags the object as killed.
C562 OR (IX+$0D) Set it in the extra flags of the object, if the other object kills what runs into it.
C565 LD (IX+$0D),A
Pass speeds if this object can be moved. Flag the other object as touched if the player is standing on it.
C568 BIT 2,(IX+$07) Jump to BlockMovementInZ_Slow if the object cannot be moved.
C56C JR Z,BlockMovementInZ_Slow
C56E LD A,(IX+$00) Fetch the sprite number and subtract 10.
C571 SUB $10
C573 CP $20 Jump to BlockMovementInZ_Carry if it is not the player.
C575 JR NC,BlockMovementInZ_Carry
C577 SET 3,(IY+$0D) Flag the other object as touched.
Give the speed along z to the other object, and take its speeds along x and y if this object has none.
BlockMovementInZ_Carry C57B LD A,(IX+$0B) Give the speed along z to the other object.
C57E LD (IY+$0B),A
C581 LD A,(IX+$09) Fetch the speed along x and test it.
C584 AND A
C585 JR NZ,BlockMovementInZ_Y Jump to BlockMovementInZ_Y if it has one.
C587 LD A,(IY+$09) Take the speed along x of the other object.
C58A LD (IX+$09),A
BlockMovementInZ_Y C58D LD A,(IX+$0A) Fetch the speed along y and test it.
C590 AND A
C591 JR NZ,BlockMovementInZ_Slow Jump to BlockMovementInZ_Slow if it has one.
C593 LD A,(IY+$0A) Take the speed along y of the other object.
C596 LD (IX+$0A),A
Slow the move along z and test this object again.
BlockMovementInZ_Slow C599 LD A,H Fetch the speed along z.
C59A CALL BringSpeedCloserToZero Bring it closer to zero.
C59D LD H,A Store it.
C59E RET Z Return if the speed is now zero.
C59F JR BlockMovementInZ_Test Jump to BlockMovementInZ_Test.
Move on to the next object.
BlockMovementInZ_Advance C5A1 LD DE,$0020 Point IY at the next object.
C5A4 ADD IY,DE
C5A6 DJNZ BlockMovementInZ_Next Jump to BlockMovementInZ_Next until all of the objects have been tested.
C5A8 RET Return.
View the equivalent code in;
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