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Routines |
| Prev: B2CC | Up: Map | Next: B399 |
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Used by the routines at DrawItems and TestRecordsAgainstEntity.
Tests whether the entity in IX overlaps the 14-byte record in IY. If it does then bit 7 of field 0A of the record is set.
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The record's drawing position, plus its third size, has to meet the entity on z. The addresses in bytes 10 and 12 then have to meet it on x and y.
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| TestRecordOverlap | B2EB | LD B,$00 | Start with no high byte. | |||||||
| B2ED | LD H,(IY+$08) | Read the record's drawing position. | ||||||||
| B2F0 | LD L,(IY+$09) | |||||||||
| B2F3 | LD C,(IY+$0D) | Add the third size and step back one. | ||||||||
| B2F6 | ADD HL,BC | |||||||||
| B2F7 | DEC HL | |||||||||
| B2F8 | LD D,(IX+$08) | Subtract the entity's z. | ||||||||
| B2FB | LD E,(IX+$09) | |||||||||
| B2FE | XOR A | No overlap when the record is below the entity on z. | ||||||||
| B2FF | SBC HL,DE | |||||||||
| B301 | RET C | |||||||||
| B302 | LD A,(IX+$0D) | Add the z extent to that z. | ||||||||
| B305 | ADD A,E | |||||||||
| B306 | LD E,A | |||||||||
| B307 | JR NC,TestRecordOverlap_X | Count the carry in the high byte. | ||||||||
| B309 | INC D | |||||||||
| TestRecordOverlap_X | B30A | LD H,(IX+$02) | Subtract it from the entity's x. | |||||||
| B30D | LD L,(IX+$03) | |||||||||
| B310 | AND A | |||||||||
| B311 | SBC HL,DE | |||||||||
| B313 | LD D,(IY+$10) | Subtract the address in bytes 10 and 11. | ||||||||
| B316 | LD E,(IY+$11) | |||||||||
| B319 | XOR A | The entity is on the far side of that address. | ||||||||
| B31A | SBC HL,DE | |||||||||
| B31C | JR C,TestRecordOverlap_MissX | |||||||||
| B31E | OR H | No overlap when it is a byte or more past the address. | ||||||||
| B31F | RET NZ | |||||||||
| B320 | LD A,L | No overlap when the gap is at least byte 4 of the record. | ||||||||
| B321 | SUB (IY+$04) | |||||||||
| B324 | RET NC | |||||||||
| B325 | JR TestRecordOverlap_Y | Join the y test. | ||||||||
| TestRecordOverlap_MissX | B327 | INC H | No overlap when the miss is a byte or more the other way. | |||||||
| B328 | RET NZ | |||||||||
| B329 | LD A,L | The x extent reaches the address. | ||||||||
| B32A | ADD A,(IX+$0B) | |||||||||
| B32D | JR C,TestRecordOverlap_Y | |||||||||
| B32F | ADD A,(IX+$0D) | The z extent reaches it too. | ||||||||
| B332 | RET NC | No overlap when it still falls short. | ||||||||
| TestRecordOverlap_Y | B333 | LD D,(IX+$08) | Add the entity's z to its y. | |||||||
| B336 | LD E,(IX+$09) | |||||||||
| B339 | LD H,(IX+$05) | |||||||||
| B33C | LD L,(IX+$06) | |||||||||
| B33F | ADD HL,DE | |||||||||
| B340 | LD D,(IY+$12) | Subtract the address in bytes 12 and 13. | ||||||||
| B343 | LD E,(IY+$13) | |||||||||
| B346 | XOR A | |||||||||
| B347 | SBC HL,DE | |||||||||
| B349 | JR C,TestRecordOverlap_MissY | The entity is on the far side of that address. | ||||||||
| B34B | OR H | No overlap when it is a byte or more past the address. | ||||||||
| B34C | RET NZ | |||||||||
| B34D | LD A,L | No overlap when the gap is at least byte 7 of the record. | ||||||||
| B34E | SUB (IY+$07) | |||||||||
| B351 | RET NC | |||||||||
| B352 | JR TestRecordOverlap_Range | Join the column test. | ||||||||
| TestRecordOverlap_MissY | B354 | INC H | No overlap when the miss is a byte or more the other way. | |||||||
| B355 | RET NZ | |||||||||
| B356 | LD A,L | The y extent reaches the address. | ||||||||
| B357 | ADD A,(IX+$0C) | |||||||||
| B35A | JR C,TestRecordOverlap_Range | |||||||||
| B35C | ADD A,(IX+$0D) | The z extent reaches it too. | ||||||||
| B35F | RET NC | No overlap when it still falls short. | ||||||||
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The column is tested against the record's origin, shifted by how far the view origin has moved. The width is the sprite width in bytes times eight, and the range is the two sizes or 20 whichever is larger.
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| TestRecordOverlap_Range | B360 | LD B,(IY+$00) | Read the record's origin. | |||||||
| B363 | LD C,(IY+$01) | |||||||||
| B366 | LD DE,($5CE7) | Fetch the view origin. | ||||||||
| B36A | LD HL,($B16A) | Fetch the origin kept for the items. | ||||||||
| B36D | XOR A | Subtract the kept origin. | ||||||||
| B36E | SBC HL,DE | |||||||||
| B370 | ADD HL,BC | Add the record's origin. | ||||||||
| B371 | LD D,$80 | Measure the column from page 80. | ||||||||
| B373 | LD E,(IX+$0E) | |||||||||
| B376 | LD A,(IX+$16) | Read the sprite width. | ||||||||
| B379 | AND %00001111 | Use the low nibble. | ||||||||
| B37B | ADD A,A | Turn the width into pixels, eight per byte. | ||||||||
| B37C | ADD A,A | |||||||||
| B37D | ADD A,A | |||||||||
| B37E | LD B,A | |||||||||
| B37F | LD A,(IY+$0B) | Add the two sizes. | ||||||||
| B382 | ADD A,(IY+$0C) | |||||||||
| B385 | JR NC,TestRecordOverlap_Minimum | |||||||||
| B387 | LD A,$FF | Use FF when the sizes overflow. | ||||||||
| TestRecordOverlap_Minimum | B389 | CP $20 | Use at least 20. | |||||||
| B38B | JR NC,TestRecordOverlap_Column | |||||||||
| B38D | LD A,$20 | The minimum size is 20. | ||||||||
| TestRecordOverlap_Column | B38F | LD C,A | Test the column against that range. | |||||||
| B390 | CALL TestRange | |||||||||
| B393 | RET NZ | Return when the column is outside it. | ||||||||
| B394 | SET 7,(IY+$0A) | Mark the record as overlapping. | ||||||||
| B398 | RET | Return. | ||||||||
| Prev: B2CC | Up: Map | Next: B399 |