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Routines |
| Prev: 8F96 | Up: Map | Next: 900A |
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Used by the routine at ControlPlayer.
Checks whether an entity could move along each axis without leaving the room. If the position it would be at is inside the room then the flag for the axis in offset 02 is cleared (bit 4 for X and bit 5 for Y), so that ApplyMovement will move it. The position is inside the room when the distance from the centre of the room (58 across and 68 down) is less than the width and the height in CurrentRoom_Width.
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| CheckRoomBounds | 8FCA | PUSH DE | Stash the moves on the stack. | |||||||
| 8FCB | LD A,E | Fetch the X move. | ||||||||
| 8FCC | ADD A,(IX+$03) | Add the X position of the entity. | ||||||||
| 8FCF | LD E,A | Keep the new X position in E. | ||||||||
| 8FD0 | LD D,(IX+$04) | Fetch the Y position of the entity. | ||||||||
| 8FD3 | LD B,$10 | B=10 (the flag for the X axis). | ||||||||
| 8FD5 | CALL CheckRoomBounds_Position | Call CheckRoomBounds_Position to check whether the position is inside the room. | ||||||||
| 8FD8 | POP DE | Restore the moves from the stack. | ||||||||
| 8FD9 | PUSH DE | Stash it on the stack again. | ||||||||
| 8FDA | LD E,(IX+$03) | Fetch the X position of the entity. | ||||||||
| 8FDD | LD A,D | Fetch the Y move. | ||||||||
| 8FDE | ADD A,(IX+$04) | Add the Y position of the entity. | ||||||||
| 8FE1 | LD D,A | Keep the new Y position in D. | ||||||||
| 8FE2 | LD B,$20 | B=20 (the flag for the Y axis). | ||||||||
| 8FE4 | CALL CheckRoomBounds_Position | Call CheckRoomBounds_Position to check whether the position is inside the room. | ||||||||
| 8FE7 | POP DE | Restore the moves from the stack. | ||||||||
| 8FE8 | RET | Return. | ||||||||
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Clears a flag if a position is inside the room.
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| CheckRoomBounds_Position | 8FE9 | LD HL,$5E1D | Point HL at the room width at CurrentRoom_Width. | |||||||
| 8FEC | LD A,E | Fetch the X position to check. | ||||||||
| 8FED | SUB $58 | Subtract 58 (the horizontal centre of the room). | ||||||||
| 8FEF | JP P,CheckRoomBounds_Width | Jump to CheckRoomBounds_Width if the result is positive. | ||||||||
| 8FF2 | NEG | Make the result positive. | ||||||||
| CheckRoomBounds_Width | 8FF4 | CP (HL) | Compare it with the width of the room. | |||||||
| 8FF5 | RET NC | Return if it is outside. | ||||||||
| 8FF6 | INC HL | Move HL on to the height of the room. | ||||||||
| 8FF7 | LD A,D | Fetch the Y position to check. | ||||||||
| 8FF8 | SUB $68 | Subtract 68 (the vertical centre of the room). | ||||||||
| 8FFA | JP P,CheckRoomBounds_Height | Jump to CheckRoomBounds_Height if the result is positive. | ||||||||
| 8FFD | NEG | Make the result positive. | ||||||||
| CheckRoomBounds_Height | 8FFF | CP (HL) | Compare it with the height of the room. | |||||||
| 9000 | RET NC | Return if it is outside. | ||||||||
| 9001 | LD A,B | Fetch the flag for the axis. | ||||||||
| 9002 | CPL | Invert the flag, to make a mask. | ||||||||
| 9003 | AND (IX+$02) | Clear the flag in offset 02 of the entity. | ||||||||
| 9006 | LD (IX+$02),A | Write the result back to offset 02. | ||||||||
| 9009 | RET | Return. | ||||||||
| Prev: 8F96 | Up: Map | Next: 900A |