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Routines |
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Used by the routines at DrawBlockRow and TestBlockRow_Draw.
Flips the data of a block horizontally, by reversing the bits of each byte with the table at 63744 and swapping the bytes. The flag in bit 7 of the first byte is changed to record the flip. This version is for blocks that are 16 pixels wide.
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The first byte of the tile is a flag. A row size other than 16 is flipped by FlipWideBlockData instead. The mirror of each byte is on page 249.
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| FlipBlockData | 50466 | LD A,(HL) | Read the tile's flag. | |||||||
| 50467 | XOR %10000000 | Toggle its top bit. | ||||||||
| 50469 | LD (HL),A | Write the flag back. | ||||||||
| 50470 | PUSH HL | Remember the tile and move past the flag. | ||||||||
| 50471 | INC HL | |||||||||
| 50472 | PUSH DE | Remember the addresses. | ||||||||
| 50473 | PUSH BC | |||||||||
| 50474 | LD A,(IY+5) | Read the row size. | ||||||||
| 50477 | CP 16 | The narrow flip is for a row size of 16. | ||||||||
| 50479 | LD (50512),SP | Remember the stack pointer. | ||||||||
| 50483 | JP NZ,FlipWideBlockData | Flip a wide tile when the row size differs. | ||||||||
| 50486 | LD A,(IY+6) | Read the tile through the stack. The count is the position byte. | ||||||||
| 50489 | LD SP,HL | |||||||||
| 50490 | LD H,249 | Use the mirror table on page 249. | ||||||||
| FlipBlockData_Loop | 50492 | EX AF,AF' | Remember how many rows remain. | |||||||
| 50493 | POP DE | Mirror four bytes of the tile. | ||||||||
| 50494 | POP BC | |||||||||
| 50495 | LD L,E | |||||||||
| 50496 | LD E,(HL) | |||||||||
| 50497 | LD L,D | |||||||||
| 50498 | LD D,(HL) | |||||||||
| 50499 | LD L,C | |||||||||
| 50500 | LD C,(HL) | |||||||||
| 50501 | LD L,B | |||||||||
| 50502 | LD B,(HL) | |||||||||
| 50503 | PUSH DE | |||||||||
| 50504 | PUSH BC | |||||||||
| 50505 | POP DE | |||||||||
| 50506 | POP DE | |||||||||
| 50507 | EX AF,AF' | Bring the count back. | ||||||||
| 50508 | DEC A | Repeat for the remaining rows. | ||||||||
| 50509 | JR NZ,FlipBlockData_Loop | |||||||||
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This entry point is used by the routine at FlipWideBlockData.
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| FlipBlockData_Exit | 50511 | LD SP,0 | Restore the stack pointer. | |||||||
| 50514 | POP BC | Restore the saved registers. | ||||||||
| 50515 | POP DE | |||||||||
| 50516 | POP HL | |||||||||
| 50517 | RET | Return. | ||||||||
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