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Routines |
| Prev: 8C4A | Up: Map | Next: 8D6B |
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Used by the routine at 8912.
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| 8D33 | CALL $8D6B | Fill the buffer at 5E00 with attribute bytes for the current room | ||
| 8D36 | LD IX,$5E00 | Point IX at the first byte of the attribute buffer at 5E00 | ||
| 8D3A | LD A,$70 | Set the operand of the 'LD D,n' instruction at 8D5C (below) to $70 | ||
| 8D3C | LD ($8D5D),A | |||
| 8D3F | CALL $8D4B | Draw the tiles for the top half of the room to the screen buffer at 7000 | ||
| 8D42 | LD IX,$5F00 | Point IX at the 256th byte of the attribute buffer at 5E00 in preparation for drawing the bottom half of the room; this instruction is redundant, since IX already holds 5F00 | ||
| 8D46 | LD A,$78 | Set the operand of the 'LD D,n' instruction at 8D5C (below) to $78 | ||
| 8D48 | LD ($8D5D),A | |||
| 8D4B | LD C,$00 | C will count 256 tiles | ||
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The following loop draws 256 tiles (for either the top half or the bottom half of the room) to the screen buffer at 7000.
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| 8D4D | LD E,C | E holds the LSB of the screen buffer address | ||
| 8D4E | LD A,(IX+$00) | Pick up an attribute byte from the buffer at 5E00; this identifies the type of tile (background, floor, wall, nasty, ramp or conveyor) to be drawn | ||
| 8D51 | LD HL,$80A0 | Move HL through the attribute bytes and graphic data of the background, floor, wall, nasty, ramp and conveyor tiles starting at 80A0 until we find a byte that matches the attribute byte of the tile to be drawn; note that if a graphic data byte matches the attribute byte being searched for, the CPIR instruction can exit early, which is a bug | ||
| 8D54 | LD BC,$0036 | |||
| 8D57 | CPIR | |||
| 8D59 | LD C,E | Restore the value of the tile counter in C | ||
| 8D5A | LD B,$08 | There are eight bytes in the tile | ||
| 8D5C | LD D,$00 | This instruction is set to either 'LD D,$70' or 'LD D,$78' above; now DE holds the appropriate address in the screen buffer at 7000 | ||
| 8D5E | LD A,(HL) | Copy the tile graphic data to the screen buffer at 7000 | ||
| 8D5F | LD (DE),A | |||
| 8D60 | INC HL | |||
| 8D61 | INC D | |||
| 8D62 | DJNZ $8D5E | |||
| 8D64 | INC IX | Move IX along to the next byte in the attribute buffer | ||
| 8D66 | INC C | Have we drawn 256 tiles yet? | ||
| 8D67 | JP NZ,$8D4D | If not, jump back to draw the next one | ||
| 8D6A | RET | |||
| Prev: 8C4A | Up: Map | Next: 8D6B |