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Routines |
Prev: 23296 | Up: Map |
Used by the routine at 25810.
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24576 | EXX | ||||||
24577 | LD HL,22558 | Point HL' and DE' at the rightmost end of the top row of attribute bytes on the screen | |||||
24580 | LD DE,22559 | ||||||
24583 | LD BC,31 | We need to scroll 31 attribute bytes at a time | |||||
24586 | EXX | ||||||
24587 | LD HL,16414 | Point HL and DE at the rightmost end of the top row of pixels on the screen | |||||
24590 | LD DE,16415 | ||||||
24593 | LD BC,31 | We need to scroll 31 display file bytes at a time | |||||
24596 | LD A,21 | There are 21 rows of character squares to scroll | |||||
24598 | EX AF,AF' | ||||||
24599 | LD A,8 | Each row of character squares contains 8 rows of pixels | |||||
24601 | PUSH HL | ||||||
24602 | PUSH DE | ||||||
24603 | LDDR | Scroll a row of pixels right one column | |||||
24605 | POP DE | ||||||
24606 | POP HL | ||||||
24607 | LD C,31 | BC=31 | |||||
24609 | INC H | Point HL and DE at the next row of pixels | |||||
24610 | INC D | ||||||
24611 | DEC A | Next row in this block of 8x32 | |||||
24612 | JR NZ,24601 | Jump back until this 8x32 pixel block has been scrolled | |||||
24614 | EXX | ||||||
24615 | LDDR | Scroll a row of attribute bytes right one column | |||||
24617 | LD C,63 | Point HL' and DE' at the rightmost end of the next row of attribute bytes on the screen | |||||
24619 | ADD HL,BC | ||||||
24620 | EX DE,HL | ||||||
24621 | ADD HL,BC | ||||||
24622 | EX DE,HL | ||||||
24623 | LD C,31 | BC'=31 | |||||
24625 | EXX | ||||||
24626 | LD A,32 | Point HL and DE at the rightmost end of the top row of the next 8x32 block of pixels | |||||
24628 | ADD A,E | ||||||
24629 | LD E,A | ||||||
24630 | LD A,32 | ||||||
24632 | ADD A,L | ||||||
24633 | LD L,A | ||||||
24634 | EX AF,AF' | ||||||
24635 | DEC A | Next row of character squares | |||||
24636 | JR Z,24654 | Exit this loop if all 21 rows have been scrolled right | |||||
24638 | CP 13 | Have we reached the middle third of the screen? | |||||
24640 | JR Z,24598 | Jump if so | |||||
24642 | CP 5 | Have we reached the bottom third of the screen? | |||||
24644 | JR Z,24598 | Jump if so | |||||
24646 | EX AF,AF' | ||||||
24647 | LD A,H | Point HL and DE at the rightmost end of the top row of the next 8x32 block of pixels | |||||
24648 | SUB 8 | ||||||
24650 | LD H,A | ||||||
24651 | LD D,A | ||||||
24652 | JR 24599 | Jump back to deal with the next row of character squares | |||||
The 21 rows of character squares have been scrolled one place to the right. Now the leftmost column needs to be filled.
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24654 | EXX | ||||||
24655 | LD HL,22528 | Point HL' and DE' at the attribute file and display file addresses for the top left of the screen, and set BC'=32; however, these values are not used | |||||
24658 | LD DE,16384 | ||||||
24661 | INC C | ||||||
24662 | EXX | ||||||
24663 | LD A,(32512) | A=leftmost column of the skool on-screen (0-64) | |||||
24666 | DEC A | We are scrolling one column right | |||||
24667 | LD (32512),A | ||||||
This entry point is used by the routine at 24731 with A holding the x-coordinate of the rightmost column of the skool on-screen (31-95).
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24670 | LD E,A | E=X (x-coordinate of the far left or far right column of the skool currently on-screen) | |||||
24671 | LD D,152 | D=Y (152=y-coordinate of the top row of the screen) | |||||
24673 | LD B,21 | There are 21 rows (152<=Y<=172) on the screen | |||||
24675 | PUSH DE | ||||||
24676 | PUSH BC | ||||||
24677 | CALL 24843 | Print the character square at (X,Y) | |||||
24680 | POP BC | ||||||
24681 | POP DE | ||||||
24682 | LD A,H | Point HL at the attribute file address corresponding to the skool coordinates (X,Y) | |||||
24683 | RRCA | ||||||
24684 | RRCA | ||||||
24685 | RRCA | ||||||
24686 | ADD A,79 | ||||||
24688 | LD H,A | ||||||
24689 | SET 7,E | Point DE at the attribute byte for the skool coordinates (X,Y) | |||||
24691 | LD A,(DE) | Pick the attribute byte up in A | |||||
24692 | RES 7,E | Restore the skool coordinates (X,Y) to DE | |||||
24694 | LD (HL),A | Poke the attribute byte onto the screen | |||||
24695 | INC D | Next row (Y) of the screen | |||||
24696 | DJNZ 24675 | Jump back until all 21 rows are done | |||||
24698 | RET |
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