Knight Tyme (48k): Routine at 52635

52635: Room drawing: Draw a graphic

Used by the routines at 52513 and 52535.

Input
BC	x- and y-coordinates
HL	(Entry at 52642 only) Address in display file to start drawing

52635

LD (23444),BC

Store x- and y-coordinates of character block currently being drawn at 23444

52639

CALL 54132

Move virtual cursor (bitmap) to display file address for coordinates x=C, y=B and load address into HL

This entry point is used by the routine at 52596.

52642

PUSH HL

Store HL (address in display file to print character)

52643

LD HL,52717

Load HL with 52717 (address of routine to advance HL with apply-horizontal-mirror flag reset)

52646

LD A,(23450)

Load A with apply-horizontal-mirror and apply-vertical-mirror flags

52649

AND 2

If apply-horizontal-mirror flag is reset...

52651

JR Z,52656

...then skip ahead to 52656

52653

LD HL,52820

Load HL with 52820 (address of routine to advance HL with apply-horizontal-mirror flag set)

52656

LD (52715),HL

Change destination for JP instruction at 52714 to value in HL...

52659

POP HL

Restore HL (address in display file to print character)

52660

LD DE,(23447)

Load DE with graphic data address

This entry point is used by the routine at 52689.

52664

LD A,(DE)

Load A with a byte of graphic data

52665

OR A

If data is zero...

52666

JR Z,52689

...then read repeat counter value, x, and draw x rows of reset pixels

52668

CP 255

If data is 255...

52670

JR Z,52710

...then read repeat counter value, x, and draw x rows of set pixels

The three-byte instruction at 52672 is modified by the instructions at 52514, 52537, 52567 and 52598. Initially it is as shown below, however upon modification it can take the following forms:

Instruction	Mirror options	Effect
52514	None	NOP / NOP / NOP (do nothing)
52537	Apply vertical	CALL 52924 (reverse the order of the bits in A)
52567	Apply horizontal	NOP / NOP / NOP (do nothing)
52598	Both	CALL 52924 (reverse the order of the bits in A)