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Routines |
Prev: 24699 | Up: Map |
Used by the routine at 25820.
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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.
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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 |
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