| Routines

E80E: Scroll the screen left 8 columns

Used by the routine at F1BA.
E80E | LD HL,$E7EC | Set the instruction at E7EB to 'LD BC,$001F'
E811 | LD (HL),$1F
E813 | LD L,$EF | Set the instruction at E7EE to 'LDIR'
E815 | LD (HL),$B0
E817 | LD B,$08 | There are 8 columns to scroll on
E819 | PUSH BC | Save the column counter
E81A | LD B,$14 | There are 20 rows to be scrolled left
E81C | LD HL,$5801 | Point HL at the attribute byte for the cell at screen coordinates (1,0)
E81F | LD D,H | Point DE at the attribute byte for the adjacent cell on the left
E820 | LD E,L
E821 | DEC E
E822 | PUSH BC | Save the row counter
E823 | PUSH HL | Save the source attribute file address
E824 | CALL $E7E8 | Shift this row of the screen left
E827 | POP HL | Restore the source attribute file address to HL
E828 | LD C,$20 | Point HL at the next row down in the attribute file
E82A | ADD HL,BC
E82B | POP BC | Restore the row counter to B
E82C | DJNZ $E81F | Jump back until all 20 rows have been scrolled left
E82E | LD HL,$7FFE | 7FFE holds the x-coordinate of the leftmost column of the play area on screen
E831 | INC (HL) | Increment this x-coordinate
E832 | LD HL,$131F | L=31 (rightmost screen column), H=19 (bottom row of the screen)
E835 | PUSH HL | Save the screen coordinates
E836 | CALL $E70C | Print a tile at screen coordinates (31,H)
E839 | POP HL | Restore the screen coordinates to HL
E83A | DEC H | Have we printed every tile in the column yet?
E83B | JP P,$E835 | Jump back if not
E83E | POP BC | Restore the column counter to B
E83F | DJNZ $E819 | Jump back until 8 columns have been scrolled on
E841 | RET |