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Routines |
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D | y-coordinate of location to check |
E | 128 + x-coordinate of location to check |
62674 | LD HL,32512 | 32512 holds the leftmost column of the skool on screen (0-64) |
62677 | LD A,E | Set A to the true x-coordinate of the potential target |
62678 | AND 127 | |
62680 | SUB (HL) | Return with the carry flag set if the pellet is off-screen to the left |
62681 | RET C | |
62682 | CP 32 | The screen is 32 columns wide |
62684 | CCF | Return with carry flag set if the pellet is off-screen to the right |
62685 | RET C | |
The potential target is on-screen.
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62686 | LD L,A | L=screen x-coordinate (0-31) of the potential target |
62687 | LD A,D | A=screen y-coordinate (2, 8 or 14) of the potential target |
62688 | SUB 152 | |
62690 | RRCA | A=64 (top floor), 1 (middle floor), or 193 (bottom floor |
62691 | RRCA | |
62692 | RRCA | |
62693 | LD H,A | Save this floor indicator in H for now |
62694 | AND 224 | A=64 (top floor), 0 (middle) or 192 (bottom) |
62696 | ADD A,L | Add the screen x-coordinate to get the LSB of the attribute file address of the potential target |
62697 | LD L,A | Copy the LSB to L |
62698 | LD A,H | A=0 (top floor) or 1 (middle floor or bottom floor) |
62699 | AND 3 | |
62701 | ADD A,88 | Add 88 to get the MSB of the attribute file address of the potential target |
62703 | LD H,A | Copy the MSB to H |
62704 | RET | Return with the carry flag reset |
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