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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 01 or 02 (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 10 and their Y positions are close enough. The vertical limit is 12 when Robbie is lower down the screen than the bug, or the bug's height (from *IX+07) when the bug is lower down.
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| BugCollision | 72F5 | LD HL,$5E6C | HL=State_Robbie_Active (Robbie). | |||||||||||
| 72F8 | LD E,$00 | E=00 (the default result, no collision). | ||||||||||||
| 72FA | LD A,(HL) | Fetch Robbie's state. | ||||||||||||
| 72FB | AND %00111111 | Keep only bits 0-5. | ||||||||||||
| 72FD | DEC A | Decrease the state of Robbie by one (zero if he is empty-handed). | ||||||||||||
| 72FE | JR Z,BugCollision_X | Jump to BugCollision_X if Robbie is empty-handed (state 01). | ||||||||||||
| 7300 | DEC A | Decrease A by one again. | ||||||||||||
| 7301 | RET NZ | Return if Robbie is not carrying a can (state 02). | ||||||||||||
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Check the horizontal distance.
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| BugCollision_X | 7302 | INC HL | A=Robbie's X position (from State_Robbie_Pos_X). | |||||||||||
| 7303 | LD A,(HL) | |||||||||||||
| 7304 | SUB (IX+$01) | Subtract the bug's X position. | ||||||||||||
| 7307 | JP P,BugCollision_Test_X | Make sure the difference is positive. | ||||||||||||
| 730A | NEG | |||||||||||||
| BugCollision_Test_X | 730C | CP $10 | Return if the difference is 10 or more. | |||||||||||
| 730E | RET NC | |||||||||||||
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Check the vertical distance.
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| 730F | 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 | 7310 | LD A,(HL) | A=Robbie's Y position (from State_Robbie_Pos_Y). | |||||||||||
| 7311 | SUB (IX+$02) | Subtract the bug's Y position. | ||||||||||||
| 7314 | JP P,BugCollision_SetHeight | Jump to BugCollision_SetHeight if Robbie is lower down the screen than the bug. | ||||||||||||
| 7317 | NEG | Make the difference positive. | ||||||||||||
| 7319 | LD D,(IX+$07) | D=the bug's height (from *IX+07). | ||||||||||||
| 731C | JR BugCollision_Test_Y | Jump to BugCollision_Test_Y. | ||||||||||||
| BugCollision_SetHeight | 731E | LD D,$12 | D=12. | |||||||||||
| BugCollision_Test_Y | 7320 | CP D | Return if the difference is D or more. | |||||||||||
| 7321 | RET NC | |||||||||||||
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A collision has been detected.
See Immunity.
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| 7322 | LD E,$01 | E=01. | ||||||||||||
| 7324 | RET | Return. | ||||||||||||
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