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7591: Insert a pixel column into a graphic buffer
Used by the routine at 755A. Slides the current contents of a row of the graphic buffer (at EB00, EC00 or ED00) one pixel to the left, and places the new pixel column into the slot freed up on the right.
A Pixel column byte
DE Graphic buffer address
7591 PUSH DE
7592 EXX
7593 POP HL HL'=graphic buffer address
7594 LD C,$08 There are 8 pixels to insert into the column
7596 LD B,$08 There are 8 bytes per row in the buffer
7598 RRCA Push a pixel into the carry flag
7599 RL (HL) Drag the pixel from the carry flag into the buffer, and slide all the other pixels in the row one to the left
759C DJNZ $7599
759E DEC C Next pixel
759F JR NZ,$7596 Jump back until all 8 pixels have been inserted
75A1 EXX
75A2 RET
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