![]() |
Routines |
Prev: 24699 | Up: Map | Next: 24825 |
Used by the routine at 25820.
|
||
24731 | EXX | |
24732 | LD HL,22529 | Point HL' and DE' at the leftmost end of the top row of attribute bytes on the screen |
24735 | LD DE,22528 | |
24738 | LD BC,31 | We need to scroll 31 attribute bytes at a time |
24741 | EXX | |
24742 | LD HL,16385 | Point HL and DE at the leftmost end of the top row of pixels on the screen |
24745 | LD DE,16384 | |
24748 | LD BC,31 | We need to scroll 31 display file bytes at a time |
24751 | LD A,21 | There are 21 rows of character squares to scroll |
24753 | EX AF,AF' | |
24754 | LD A,8 | Each row of character squares contains 8 rows of pixels |
24756 | PUSH HL | |
24757 | PUSH DE | |
24758 | LDIR | Scroll a row of pixels left one column |
24760 | POP DE | |
24761 | POP HL | |
24762 | INC D | Point HL and DE at the next row of pixels |
24763 | INC H | |
24764 | LD C,31 | BC=31 |
24766 | DEC A | Next row in this block of 8x32 |
24767 | JR NZ,24756 | Jump back until this 8x32 pixel block has been scrolled |
24769 | EXX | |
24770 | LDIR | Scroll a row of attribute bytes left one column |
24772 | INC HL | Point HL' and DE' at the leftmost end of the next row of attribute bytes on the screen |
24773 | INC DE | |
24774 | LD C,31 | BC'=31 |
24776 | EXX | |
24777 | LD A,32 | Point HL and DE at the leftmost end of the top row of the next 8x32 block of pixels |
24779 | ADD A,E | |
24780 | LD E,A | |
24781 | LD A,32 | |
24783 | ADD A,L | |
24784 | LD L,A | |
24785 | EX AF,AF' | |
24786 | DEC A | Next row of character squares |
24787 | JR Z,24805 | Exit this loop if all 21 rows have been scrolled left |
24789 | CP 5 | Have we reached the bottom third of the screen? |
24791 | JR Z,24753 | Jump if so |
24793 | CP 13 | Have we reached the middle third of the screen? |
24795 | JR Z,24753 | Jump if so |
24797 | EX AF,AF' | |
24798 | LD A,H | Point HL and DE at the leftmost end of the top row of the next 8x32 block of pixels |
24799 | SUB 8 | |
24801 | LD H,A | |
24802 | LD D,A | |
24803 | JR 24754 | Jump back to deal with the next row of character squares |
The 21 rows of character squares have been scrolled one place to the left. Now the rightmost column needs to be filled.
|
||
24805 | EXX | |
24806 | LD HL,22559 | Point HL' and DE' at the attribute file and display file addresses for the top right of the screen, and set BC'=32; however, these values are not used |
24809 | LD DE,16415 | |
24812 | INC C | |
24813 | EXX | |
24814 | LD A,(32512) | A=leftmost column of the skool on-screen (0-64) |
24817 | INC A | We are scrolling one column left |
24818 | LD (32512),A | |
24821 | ADD A,C | A=rightmost column of the skool on-screen (31-95) |
24822 | JP 24670 | Fill in the rightmost column |
Prev: 24699 | Up: Map | Next: 24825 |