| Routines

7DD8: Insert a pixel column into the top or bottom half of the speech bubble text window

Used by the routine at 7302. Slides the current contents of the top or bottom half of the speech bubble text window one pixel to the left, and places the new pixel column (4 pixels high) into the slot freed up on the right.
Input
A | Pixel column byte
HL | Display file address
7DD8 | LD B,$04 | There are four pixel rows to slide left
7DDA | PUSH BC | Save the pixel row counter
7DDB | LD C,L | Save L in C briefly
7DDC | LD B,$06 | The text window is six bytes wide
7DDE | RLCA | Push a pixel into the carry flag
7DDF | RL (HL) | Slide this pixel into a row of the text window
7DE1 | DEC HL
7DE2 | DJNZ $7DDF
7DE4 | LD L,C | Restore L
7DE5 | POP BC | Restore the pixel row counter to B
7DE6 | INC H | Move to the next row of pixels
7DE7 | DJNZ $7DDA | Jump back until all four rows of pixels have been done
7DE9 | RET |