Routines
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D76F: The byte-aligned case, and the start of its unrolled run
Used by the routine at print_sprite.
For a sprite on a byte boundary each byte of a row is one unit of eight bytes of code: the background byte, cleared under the mask with CPL / OR E / CPL, has the image ORed in and is stored. Five units run on from the POP below, and the JR at sprite_row_jump is set to enter them as many units from the end as the sprite is wide.
sprite_aligned D76F LD A,(DE) the width from the header, into byte $18
D770 INC DE
D771 AND $0F
D773 LD (IX+$18),A
D776 LD B,A the JR offset: 8 bytes of code per byte of width, back from the end of the aligned run
D777 ADD A,A
D778 ADD A,A
D779 ADD A,A
D77A NEG
D77C SUB $06
D77E JR patch_sprite_rows
D780 POP DE the first two units of the aligned run
D781 LD A,(BC)
D782 CPL
D783 OR E
D784 CPL
D785 OR D
D786 LD (BC),A
D787 INC BC
D788 POP DE
D789 LD A,(BC)
D78A CPL
D78B OR E
D78C CPL
D78D OR D
D78E LD (BC),A
D78F INC BC
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