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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 F900 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 10 pixels wide.
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The first byte of the tile is a flag. A row size other than 10 is flipped by FlipWideBlockData instead. The mirror of each byte is on page F9.
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| FlipBlockData | C522 | LD A,(HL) | Read the tile's flag. | |||||||
| C523 | XOR %10000000 | Toggle its top bit. | ||||||||
| C525 | LD (HL),A | Write the flag back. | ||||||||
| C526 | PUSH HL | Remember the tile and move past the flag. | ||||||||
| C527 | INC HL | |||||||||
| C528 | PUSH DE | Remember the addresses. | ||||||||
| C529 | PUSH BC | |||||||||
| C52A | LD A,(IY+$05) | Read the row size. | ||||||||
| C52D | CP $10 | The narrow flip is for a row size of 10. | ||||||||
| C52F | LD ($C550),SP | Remember the stack pointer. | ||||||||
| C533 | JP NZ,FlipWideBlockData | Flip a wide tile when the row size differs. | ||||||||
| C536 | LD A,(IY+$06) | Read the tile through the stack. The count is the position byte. | ||||||||
| C539 | LD SP,HL | |||||||||
| C53A | LD H,$F9 | Use the mirror table on page F9. | ||||||||
| FlipBlockData_Loop | C53C | EX AF,AF' | Remember how many rows remain. | |||||||
| C53D | POP DE | Mirror four bytes of the tile. | ||||||||
| C53E | POP BC | |||||||||
| C53F | LD L,E | |||||||||
| C540 | LD E,(HL) | |||||||||
| C541 | LD L,D | |||||||||
| C542 | LD D,(HL) | |||||||||
| C543 | LD L,C | |||||||||
| C544 | LD C,(HL) | |||||||||
| C545 | LD L,B | |||||||||
| C546 | LD B,(HL) | |||||||||
| C547 | PUSH DE | |||||||||
| C548 | PUSH BC | |||||||||
| C549 | POP DE | |||||||||
| C54A | POP DE | |||||||||
| C54B | EX AF,AF' | Bring the count back. | ||||||||
| C54C | DEC A | Repeat for the remaining rows. | ||||||||
| C54D | JR NZ,FlipBlockData_Loop | |||||||||
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This entry point is used by the routine at FlipWideBlockData.
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| FlipBlockData_Exit | C54F | LD SP,$0000 | Restore the stack pointer. | |||||||
| C552 | POP BC | Restore the saved registers. | ||||||||
| C553 | POP DE | |||||||||
| C554 | POP HL | |||||||||
| C555 | RET | Return. | ||||||||
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