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Routines |
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Used by the routine at CheckTerrainCollision.
Tests whether a box touches an object with a sloping face. Bits 6 and 7 of the byte at offset 4 of the object select one of four ways the slope can face, and the bottom three bits are the steepness. The result is stored in 23580, and when the box does touch the object the depth that it has gone into the slope is stored in 23578. The position of the box comes from 52794 and its size from 52796.
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| TestSlopeCollision | 40501 | XOR A | Clear the result. | |||||
| 40502 | LD (23580),A | Store it. | ||||||
| 40505 | LD HL,(52794) | Fetch the position of the box. | ||||||
| 40508 | LD DE,(52796) | Fetch the size of the box. | ||||||
| 40512 | LD A,(IX+4) | Fetch the slope flags. | ||||||
| 40515 | AND %00000111 | Keep the steepness. | ||||||
| 40517 | LD C,A | Store it in C. | ||||||
| 40518 | LD A,(IX+4) | Fetch the slope flags again. | ||||||
| 40521 | AND %11000000 | Keep the direction bits. | ||||||
| 40523 | JR Z,TestSlopeCollision_Down | Jump to TestSlopeCollision_Down if both are clear. | ||||||
| 40525 | CP 64 | Jump to TestSlopeCollision_Mirrored if it is the second direction. | ||||||
| 40527 | JP Z,TestSlopeCollision_Mirrored | |||||||
| 40530 | CP 128 | Jump to TestSlopeCollision_Up if it is the third direction. | ||||||
| 40532 | JP Z,TestSlopeCollision_Up | |||||||
| 40535 | CP 192 | Jump to TestSlopeCollision_UpMirrored if it is the fourth direction. | ||||||
| 40537 | JP Z,TestSlopeCollision_UpMirrored | |||||||
| 40540 | RET | Return. | ||||||
| TestSlopeCollision_Down | 40541 | CALL FindSlopeOverlap | Find the overlap with the slope. | |||||
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This entry point is used by the routine at FindMirroredSlopeOverlap.
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| TestSlopeCollision_Depth | 40544 | LD A,(23580) | Fetch the result. | |||||
| 40547 | AND A | Test it. | ||||||
| 40548 | RET Z | Return if the box does not overlap. | ||||||
| 40549 | DEC A | Reduce the result to zero. | ||||||
| 40550 | LD (23580),A | Store it. | ||||||
| 40553 | LD A,D | Fetch the width of the box. | ||||||
| 40554 | ADD A,L | Add the horizontal position. | ||||||
| 40555 | LD L,A | Store it in L. | ||||||
| 40556 | LD A,(IX+0) | Fetch the left edge of the object. | ||||||
| 40559 | ADD A,B | Add the distance up the slope. | ||||||
| 40560 | SUB L | Subtract the right edge of the box. | ||||||
| 40561 | RET NC | Return if the box is clear of the slope. | ||||||
| 40562 | NEG | Make the depth positive. | ||||||
| 40564 | LD (23578),A | Store the depth. | ||||||
| 40567 | JP SetOverlapFlag | Jump to SetOverlapFlag to say that the box touches the slope. | ||||||
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