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Routines |
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Used by the routines at UpdateFoamEntity and UpdateSaucerEntity.
Turns an entity by a step towards the heading in field 20 by changing bits 1-5 of the current heading in field 11.
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| TurnEntity | 990C | LD A,(IX+$11) | Fetch the current heading of the entity. | |||||||
| 990F | AND %00111110 | Use bits 1-5. | ||||||||
| 9911 | LD L,A | Copy it into L. | ||||||||
| 9912 | SUB (IX+$20) | Subtract the wanted heading of the entity. | ||||||||
| 9915 | RET Z | Return if the entity is already heading that way. | ||||||||
| 9916 | BIT 5,A | Test bit 5 of the difference. | ||||||||
| 9918 | LD A,B | Fetch the size of the step. | ||||||||
| 9919 | JR NZ,TurnEntity_Apply | Jump to TurnEntity_Apply if the step is to be added. | ||||||||
| 991B | NEG | Negate the step. | ||||||||
| TurnEntity_Apply | 991D | ADD A,L | Add the step to the current heading. | |||||||
| 991E | AND %00111110 | Use bits 1-5. | ||||||||
| 9920 | LD (IX+$11),A | Store the new heading of the entity. | ||||||||
| 9923 | RET | Return. | ||||||||
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