Knight Lore: Routine at C515

C515: Fill Window

Fills a rectangle of the screen buffer, or of the attribute file, with one byte. The rows of the rectangle are 20 bytes apart.

Input
A	Byte to fill the rectangle with
B	Width of the rectangle in bytes
C	Height of the rectangle in lines
HL	Address of the first byte

Fill each line of the rectangle, then move down a row.

FillWindow

C515

LD DE,$0020

Set DE to the length of a line.

FillWindow_Line

C518

PUSH BC

Stash the width and height on the stack.

C519

PUSH HL

Stash the address of the start of the line on the stack.

FillWindow_Byte

C51A

LD (HL),A

Fill a byte.

C51B

INC HL

Move on to the next byte.

C51C

Jump to FillWindow_Byte until the line is filled.

C51E

POP HL

Restore the address of the start of the line from the stack.

C51F

ADD HL,DE

Move on to the next line.

C520

POP BC

Restore the width and height from the stack.

C521

DEC C

Decrease the number of lines left.

C522

Jump to FillWindow_Line until all of the lines have been filled.

C524

RET

Return.

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