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7632: Insert a pixel column into the number graphic buffer
Used by the routine at 7646. Slides the current contents of the number graphic buffer (at D90B) one pixel to the left, and places the new pixel column into the slot freed up on the right.
A Pixel column byte
7632 LD HL,$D91F Point HL at the end of the buffer at D90B
7635 RRCA Discard the baseline bit
7636 LD C,$07 We will consider the remaining 7 bits
7638 LD B,$03 The buffer is 3 character squares wide
763A RRCA Drop a bit into the carry flag
763B RL (HL) Pick it up in the buffer and shift the other pixels in this row one to the left
763E DJNZ $763B
7640 DEC C Next bit
7641 JR NZ,$7638 Jump back until all 7 bits in the column are done
7643 RET
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