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30258: Insert a pixel column into the number graphic buffer
Used by the routine at 30278. Slides the current contents of the number graphic buffer (at 55563) one pixel to the left, and places the new pixel column into the slot freed up on the right.
A Pixel column byte
30258 LD HL,55583 Point HL at the end of the buffer at 55563
30261 RRCA Discard the baseline bit
30262 LD C,7 We will consider the remaining 7 bits
30264 LD B,3 The buffer is 3 character squares wide
30266 RRCA Drop a bit into the carry flag
30267 RL (HL) Pick it up in the buffer and shift the other pixels in this row one to the left
30269 DEC HL
30270 DJNZ 30267
30272 DEC C Next bit
30273 JR NZ,30264 Jump back until all 7 bits in the column are done
30275 RET
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