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Routines |
| Prev: F4CD | Up: Map | Next: F4F1 |
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| F4D2 | LD HL,$7F00 | 7F00 holds the leftmost column of the skool on screen (0-64) | ||||||||
| F4D5 | LD A,E | Set A to the true x-coordinate of the potential target | ||||||||
| F4D6 | AND $7F | |||||||||
| F4D8 | SUB (HL) | Return with the carry flag set if the pellet is off-screen to the left | ||||||||
| F4D9 | RET C | |||||||||
| F4DA | CP $20 | The screen is 32 columns wide | ||||||||
| F4DC | CCF | Return with carry flag set if the pellet is off-screen to the right | ||||||||
| F4DD | RET C | |||||||||
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The potential target is on-screen.
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| F4DE | LD L,A | L=screen x-coordinate (0-31) of the potential target | ||||||||
| F4DF | LD A,D | A=screen y-coordinate (2, 8 or 14) of the potential target | ||||||||
| F4E0 | SUB $98 | |||||||||
| F4E2 | RRCA | A=0x40 (top floor), 0x01 (middle floor), or 0xC1 (bottom floor | ||||||||
| F4E3 | RRCA | |||||||||
| F4E4 | RRCA | |||||||||
| F4E5 | LD H,A | Save this floor indicator in H for now | ||||||||
| F4E6 | AND $E0 | A=0x40 (top floor), 0x00 (middle) or 0xC0 (bottom) | ||||||||
| F4E8 | ADD A,L | Add the screen x-coordinate to get the LSB of the attribute file address of the potential target | ||||||||
| F4E9 | LD L,A | Copy the LSB to L | ||||||||
| F4EA | LD A,H | A=0x00 (top floor) or 0x01 (middle floor or bottom floor) | ||||||||
| F4EB | AND $03 | |||||||||
| F4ED | ADD A,$58 | Add 0x58 to get the MSB of the attribute file address of the potential target | ||||||||
| F4EF | LD H,A | Copy the MSB to H | ||||||||
| F4F0 | RET | Return with the carry flag reset | ||||||||
| Prev: F4CD | Up: Map | Next: F4F1 |