Atic Atac: Routine at 9E9B

Used by the routines at DrawEntity, RemoveEntity and DisplayEntity.

XORs the old sprite and the new sprite onto the screen one row at a time, working up from the bottom row. The row counters are in C and C' (in the normal and the shadow register sets), and each register set holds the screen address in HL and the sprite data address in DE for one of the two sprites. When the counters run out, any rows left over in Old_Sprite_Row_Count and New_Sprite_Row_Count are drawn.

Drawing a sprite a second time erases it, so the old sprite is removed from where it was and the new sprite is drawn where it is now.

Used by the routines at DrawEntity, RemoveEntity and DisplayEntity. XORs the old sprite and the new sprite onto the screen one row at a time, working up from the bottom row. The row counters are in C and C' (in the normal and the shadow register sets), and each register set holds the screen address in HL and the sprite data address in DE for one of the two sprites. When the counters run out, any rows left over in Old_Sprite_Row_Count and New_Sprite_Row_Count are drawn. Drawing a sprite a second time erases it, so the old sprite is removed from where it was and the new sprite is drawn where it is now.
XORSpriteLoop	9E9B	LD A,C	Fetch the number of rows of the old sprite that are left.
	9E9C	AND A	Jump to XORSpriteLoop_Swap if there are no rows of the old sprite left to draw.
	9E9D	JR Z,XORSpriteLoop_Swap
	9E9F	DEC C	Decrease the row counter by one.
	9EA0	CALL DrawOldSpriteRow	Call DrawOldSpriteRow to draw the old sprite row.
	9EA3	EXX	Switch to the shadow registers.
	9EA4	LD A,C	Fetch the number of rows of the new sprite that are left.
	9EA5	AND A	Jump to XORSpriteLoop_Next if there are no rows of the new sprite left to draw.
	9EA6	JR Z,XORSpriteLoop_Next
XORSpriteLoop_Actor	9EA8	DEC C	Decrease the row counter by one.
	9EA9	CALL DrawActorSpriteRow	Call DrawActorSpriteRow to draw the new sprite row.
XORSpriteLoop_Next	9EAC	EXX	Switch to the normal registers.
	9EAD	JR XORSpriteLoop	Jump to XORSpriteLoop to draw the sprites onto the screen.
XORSpriteLoop_Swap	9EAF	EXX	Switch to the shadow registers.
	9EB0	LD A,C	Fetch the number of rows of the new sprite that are left.
	9EB1	AND A	Jump to XORSpriteLoop_Actor if there are more rows of the new sprite to draw.
	9EB2	JR NZ,XORSpriteLoop_Actor
This entry point is used by the routine at DisplayEntity.
XORSpriteLoop_Restore	9EB4	EXX	Switch to the normal registers.
This entry point is used by the routine at DisplayEntity. Fetch the number of rows left over from the old sprite and the new sprite. If there are none then the drawing is finished.
XORSpriteLoop_Remaining	9EB5	LD A,($5E18)	Fetch the number of old sprite rows from Old_Sprite_Row_Count and keep it in C.
	9EB8	LD C,A
	9EB9	LD A,($5E19)	Fetch the number of new sprite rows from New_Sprite_Row_Count.
	9EBC	OR C	Return if there are no rows left to draw.
	9EBD	RET Z	Return if there are no rows left to draw.
	9EBE	XOR A	A=00.
	9EBF	LD ($5E18),A	Update the number of old sprite rows in Old_Sprite_Row_Count.
	9EC2	EXX	Switch to the shadow registers.
	9EC3	LD A,($5E19)	Fetch the number of new sprite rows from New_Sprite_Row_Count and keep it in C.
	9EC6	LD C,A
	9EC7	XOR A	A=00.
This entry point is used by the routine at DisplayEntity.
XORSpriteLoop_Continue	9EC8	LD ($5E19),A	Update the number of new sprite rows in New_Sprite_Row_Count.
	9ECB	EXX	Switch to the normal registers.
	9ECC	JR XORSpriteLoop	Jump to XORSpriteLoop to draw the sprites onto the screen.
View the equivalent code in; Cookie Sabre Wulf Underwurlde