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Routines |
| Prev: C2BA | Up: Map | Next: C352 |
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Works out which of two objects which overlap should be drawn first. For each object it finds a number from the difference between a vertical and a horizontal edge, and it swaps the objects if the numbers are the wrong way round. The edges which it uses are different when the view is rotated.
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| CompareObjectDepths | C2C5 | LD A,($A268) | Fetch the rotation of the view. | |||||||
| C2C8 | AND %00000001 | Test the lowest bit. | ||||||||
| C2CA | JR NZ,CompareObjectDepths_Rotated | Jump if the view is rotated. | ||||||||
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Find the number for the second object, in DE.
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| C2CC | LD A,(IY+$01) | Fetch the horizontal position, add the horizontal size, halve it and add 40. | ||||||||
| C2CF | ADD A,(IY+$08) | |||||||||
| C2D2 | RRA | |||||||||
| C2D3 | ADD A,$40 | |||||||||
| C2D5 | LD C,A | Keep it in BC. | ||||||||
| C2D6 | LD B,$00 | |||||||||
| C2D8 | LD A,(IY+$03) | Fetch the vertical position, subtract the vertical size, halve it and add 40. | ||||||||
| C2DB | SUB (IY+$09) | |||||||||
| C2DE | RRA | |||||||||
| C2DF | ADD A,$40 | |||||||||
| C2E1 | LD L,A | Make the top edge a sixteen bit number in HL. | ||||||||
| C2E2 | LD H,$00 | |||||||||
| C2E4 | AND A | Subtract the horizontal edge. | ||||||||
| C2E5 | SBC HL,BC | |||||||||
| C2E7 | LD BC,$0100 | Add 0100. | ||||||||
| C2EA | ADD HL,BC | |||||||||
| C2EB | SRL H | Divide the result by two... | ||||||||
| C2ED | RR L | |||||||||
| C2EF | EX DE,HL | ...and keep it in DE. | ||||||||
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Find the number for the first object, in HL, in the same way.
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| C2F0 | LD A,(IX+$01) | Fetch the horizontal position, add the horizontal size, halve it and add 40. | ||||||||
| C2F3 | ADD A,(IX+$08) | |||||||||
| C2F6 | RRA | |||||||||
| C2F7 | ADD A,$40 | |||||||||
| C2F9 | LD C,A | Keep it in BC. | ||||||||
| C2FA | LD B,$00 | |||||||||
| C2FC | LD A,(IX+$03) | Fetch the vertical position and subtract the vertical size. | ||||||||
| C2FF | SUB (IX+$09) | |||||||||
| CompareObjectDepths_Finish | C302 | RRA | Halve it and add 40. | |||||||
| C303 | ADD A,$40 | |||||||||
| C305 | LD L,A | Make the top edge a sixteen bit number in HL. | ||||||||
| C306 | LD H,$00 | |||||||||
| C308 | AND A | Subtract the horizontal edge. | ||||||||
| C309 | SBC HL,BC | |||||||||
| C30B | LD BC,$0100 | Add 0100. | ||||||||
| C30E | ADD HL,BC | |||||||||
| C30F | SRL H | Divide the result by two. | ||||||||
| C311 | RR L | |||||||||
| C313 | AND A | Subtract the number for the other object. | ||||||||
| C314 | SBC HL,DE | |||||||||
| C316 | RET NC | Return if the first number is not the lower. | ||||||||
| C317 | JP ChooseOtherObject | Otherwise swap the objects. | ||||||||
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Find the numbers when the view is rotated. The number for the first object goes in DE...
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| CompareObjectDepths_Rotated | C31A | LD A,(IX+$01) | Fetch the horizontal position, subtract the horizontal size, halve it and add 40. | |||||||
| C31D | SUB (IX+$08) | |||||||||
| C320 | RRA | |||||||||
| C321 | ADD A,$40 | |||||||||
| C323 | LD C,A | Keep it in BC. | ||||||||
| C324 | LD B,$00 | |||||||||
| C326 | LD A,(IX+$03) | Fetch the vertical position, add the vertical size, halve it and add 40. | ||||||||
| C329 | ADD A,(IX+$09) | |||||||||
| C32C | RRA | |||||||||
| C32D | ADD A,$40 | |||||||||
| C32F | LD L,A | Make the lower edge a sixteen bit number in HL. | ||||||||
| C330 | LD H,$00 | |||||||||
| C332 | AND A | Subtract the horizontal edge. | ||||||||
| C333 | SBC HL,BC | |||||||||
| C335 | LD BC,$0100 | Add 0100. | ||||||||
| C338 | ADD HL,BC | |||||||||
| C339 | SRL H | Divide the result by two... | ||||||||
| C33B | RR L | |||||||||
| C33D | EX DE,HL | ...and keep it in DE. | ||||||||
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...and the number for the second object is found in HL by the end of the routine above.
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| C33E | LD A,(IY+$01) | Fetch the horizontal position, subtract the horizontal size, halve it and add 40. | ||||||||
| C341 | SUB (IY+$08) | |||||||||
| C344 | RRA | |||||||||
| C345 | ADD A,$40 | |||||||||
| C347 | LD C,A | Keep it in BC. | ||||||||
| C348 | LD B,$00 | |||||||||
| C34A | LD A,(IY+$03) | Fetch the vertical position and add the vertical size. | ||||||||
| C34D | ADD A,(IY+$09) | |||||||||
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Go to find the number.
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| C350 | JR CompareObjectDepths_Finish | Jump to CompareObjectDepths_Finish. | ||||||||
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View the equivalent code in;
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| Prev: C2BA | Up: Map | Next: C352 |