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30097: Insert a pixel column into a graphic buffer
Used by the routine at 30042. Slides the current contents of a row of the graphic buffer (at 60160, 60416 or 60672) 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
30097 PUSH DE
30098 EXX
30099 POP HL HL'=graphic buffer address
30100 LD C,8 There are 8 pixels to insert into the column
30102 LD B,8 There are 8 bytes per row in the buffer
30104 RRCA Push a pixel into the carry flag
30105 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
30107 DEC HL
30108 DJNZ 30105
30110 DEC C Next pixel
30111 JR NZ,30102 Jump back until all 8 pixels have been inserted
30113 EXX
30114 RET
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