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Routines |
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Used by the routines at ApplyGravityAndMove and MovePlayer.
Stops an object moving through the walls of the room or through other objects. The speeds along x, y and z of the object are each brought closer to zero until the object can move without hitting anything. Whichever direction is hit is flagged in the low bits of the collision flags: bit 0 for x, bit 1 for y and bit 2 for z. For z that means the object is standing on something. An object that is flagged to be ignored is not adjusted.
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Ignore the object so that it does not hit itself, and clear the blocked flags.
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| BlockMovement | B6ED | BIT 1,(IX+$07) | Return if the object is already being moved. | |||||
| B6F1 | RET NZ | |||||||
| B6F2 | SET 1,(IX+$07) | Flag that the object is being moved. | ||||||
| B6F6 | LD A,(IX+$0C) | Fetch the collision flags. | ||||||
| B6F9 | AND %11111000 | Clear the blocked flags of x, y and z. | ||||||
| B6FB | LD (IX+$0C),A | Store the collision flags. | ||||||
| B6FE | LD L,$00 | Start with no speed along y in L and none along x in C. | ||||||
| B700 | LD C,L | |||||||
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The new speeds are kept in H for z, C for x and L for y. Test z against the floor, then other objects.
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| B701 | LD A,(IX+$0B) | Fetch the speed along z and test whether it is zero. | ||||||
| B704 | AND A | |||||||
| B705 | LD H,A | Copy it to H. | ||||||
| B706 | JR Z,BlockMovement_X | Jump to BlockMovement_X if it is zero. | ||||||
| B708 | CALL StopObjectAtFloor | Call StopObjectAtFloor to cut the speed down so that the object stays above the floor. | ||||||
| B70B | LD A,H | Jump to BlockMovement_X if that has left no speed. | ||||||
| B70C | AND A | |||||||
| B70D | JR Z,BlockMovement_X | |||||||
| B70F | CALL BlockMovementInZ | Call BlockMovementInZ to cut the speed down so that the object does not go through another object. | ||||||
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Test x against the walls of the room, then other objects.
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| BlockMovement_X | B712 | LD A,(IX+$09) | Fetch the speed along x and test whether it is zero. | |||||
| B715 | AND A | |||||||
| B716 | LD C,A | Copy it to C. | ||||||
| B717 | JR Z,BlockMovement_Y | Jump to BlockMovement_Y if it is zero. | ||||||
| B719 | CALL KeepObjectInRoomInX | Call KeepObjectInRoomInX to cut the speed down so that the object stays inside the walls. | ||||||
| B71C | LD A,C | Jump to BlockMovement_Y if that has left no speed. | ||||||
| B71D | AND A | |||||||
| B71E | JR Z,BlockMovement_Y | |||||||
| B720 | CALL BlockMovementInX | Call BlockMovementInX to cut the speed down so that the object does not go through another object. | ||||||
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Test y against the walls of the room, then other objects.
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| BlockMovement_Y | B723 | LD A,(IX+$0A) | Fetch the speed along y and test whether it is zero. | |||||
| B726 | AND A | |||||||
| B727 | LD L,A | Copy it to L. | ||||||
| B728 | JR Z,BlockMovement_Store | Jump to BlockMovement_Store if it is zero. | ||||||
| B72A | CALL KeepObjectInRoomInY | Call KeepObjectInRoomInY to cut the speed down so that the object stays inside the walls. | ||||||
| B72D | LD A,L | Jump to BlockMovement_Store if that has left no speed. | ||||||
| B72E | AND A | |||||||
| B72F | JR Z,BlockMovement_Store | |||||||
| B731 | CALL BlockMovementInY | Call BlockMovementInY to cut the speed down so that the object does not go through another object. | ||||||
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Store the new speeds and stop ignoring the object.
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| BlockMovement_Store | B734 | LD (IX+$09),C | Store the new speeds along x, y and z. | |||||
| B737 | LD (IX+$0A),L | |||||||
| B73A | LD (IX+$0B),H | |||||||
| B73D | RES 1,(IX+$07) | Flag that the object is not being moved. | ||||||
| B741 | RET | Return. | ||||||
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View the equivalent code in;
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| Prev: B6DD | Up: Map | Next: B742 |