Avalon: Routine at DC77

DC77: Draw/erase graphics - graphic tile out of bounds

Used by the routine at DB98.

Input
HL	Contains address of the vertical pixel offset in the graphic tile data

Gone 'out of bounds' on horizontal screen position so there's no need to draw this tile. Skip to the next one (checking if there are any left).

DC77

INC HL

Move HL to the next address in the graphics data

DC78

LD C,(HL)

This address contains the number of bytes in the tile graphic

DC79

INC HL

Move HL to point to the start of the graphics data itself

Also jump in at to this point from the check at DBD0, if out of bounds on vertical position (into bottom 3rd of screen)

HL	Pointing at address of first graphics byte in tile
C	Number of bytes in next tile graphic

DC7A

LD D,$00

DC7C

LD E,C

DE now contains number of bytes left to draw in the current graphics tile

DC7D

ADD HL,DE

...Add to current graphics address pointer to skip over the rest of the tile graphics (as there's no need to draw them)

Decrement the tile counter and check to see if all tiles of the graphic have been drawn

DC7E

LD A,($EAD0)

Get tile counter (number of tiles in current graphic)

DC81

DEC A

Decrement counter

DC82

LD ($EAD0),A

...and re-store

DC85

JP NZ,$DBA6

Still tiles to draw/erase? If so, go draw/erase them

DC88

RET

All graphic tiles are now drawn/erased.