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Routines |
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Used by the routine at UpdateBugCommon.
Tests whether a bug is touching Robbie. Robbie only counts when his state is 1 or 2 (empty-handed or carrying a can), so a collision cannot happen while he is exploding.
The two collide when their X positions differ by less than 16 and their Y positions are close enough. The vertical limit is 18 when Robbie is lower down the screen than the bug, or the bug's height (from *IX+7) when the bug is lower down.
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| BugCollision | 29429 | LD HL,24172 | HL=State_Robbie_Active (Robbie). | |||||||||||
| 29432 | LD E,0 | E=0 (the default result, no collision). | ||||||||||||
| 29434 | LD A,(HL) | Fetch Robbie's state. | ||||||||||||
| 29435 | AND %00111111 | Keep only bits 0-5. | ||||||||||||
| 29437 | DEC A | Decrease the state of Robbie by one (zero if he is empty-handed). | ||||||||||||
| 29438 | JR Z,BugCollision_X | Jump to BugCollision_X if Robbie is empty-handed (state 1). | ||||||||||||
| 29440 | DEC A | Decrease A by one again. | ||||||||||||
| 29441 | RET NZ | Return if Robbie is not carrying a can (state 2). | ||||||||||||
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Check the horizontal distance.
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| BugCollision_X | 29442 | INC HL | A=Robbie's X position (from State_Robbie_Pos_X). | |||||||||||
| 29443 | LD A,(HL) | |||||||||||||
| 29444 | SUB (IX+1) | Subtract the bug's X position. | ||||||||||||
| 29447 | JP P,BugCollision_Test_X | Make sure the difference is positive. | ||||||||||||
| 29450 | NEG | |||||||||||||
| BugCollision_Test_X | 29452 | CP 16 | Return if the difference is 16 or more. | |||||||||||
| 29454 | RET NC | |||||||||||||
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Check the vertical distance.
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| 29455 | INC HL | Move on to Robbie's Y position. | ||||||||||||
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This entry point is used by the routine at CreateBug.
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| BugCollision_Y | 29456 | LD A,(HL) | A=Robbie's Y position (from State_Robbie_Pos_Y). | |||||||||||
| 29457 | SUB (IX+2) | Subtract the bug's Y position. | ||||||||||||
| 29460 | JP P,BugCollision_SetHeight | Jump to BugCollision_SetHeight if Robbie is lower down the screen than the bug. | ||||||||||||
| 29463 | NEG | Make the difference positive. | ||||||||||||
| 29465 | LD D,(IX+7) | D=the bug's height (from *IX+7). | ||||||||||||
| 29468 | JR BugCollision_Test_Y | Jump to BugCollision_Test_Y. | ||||||||||||
| BugCollision_SetHeight | 29470 | LD D,18 | D=18. | |||||||||||
| BugCollision_Test_Y | 29472 | CP D | Return if the difference is D or more. | |||||||||||
| 29473 | RET NC | |||||||||||||
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A collision has been detected.
See Immunity.
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| 29474 | LD E,1 | E=1. | ||||||||||||
| 29476 | RET | Return. | ||||||||||||
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