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27008: Update the SRB for one column of a sprite
Used by the routine at 25008. Sets the bits in the screen refresh buffer (SRB) that correspond to the four tiles in the left, middle or right column of a sprite.
DE Base address of the sprite UDG references
HL SRB address corresponding to the top row of the sprite
27008 LD B,4 There are 4 rows (and 3 columns) in a sprite
27010 LD A,(DE) Pick up a sprite UDG reference
27011 INC D Next row of the sprite
27012 AND A Is this the blank UDG?
27013 JR Z,27017 Jump if so (no need to update this SRB byte)
27015 SET 0,(HL) Set the appropriate bit in the SRB byte; this instruction is modified by the routine at 25008 before this routine is called
27017 LD A,4 Point HL at the byte of the SRB corresponding to the next row of the screen
27019 ADD A,L
27020 LD L,A
27021 DJNZ 27010 Jump back until all 4 squares in the column are done
27023 BIT 3,D Return with the zero flag reset if we have just updated the SRB for the rightmost column of the sprite
27025 RET
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