The Sidney Affair: Routine at FB09

Copies one frame of the picture held in the buffer at PictureBuffer to the screen: first the pixel rows, then the attributes from PictureBuffer_Attributes. Called by BASIC as "ins" (FB09) with the frame number POKEd into DisplayFrame_Number.

The routine works out the frame's row and column in the sheet from *DisplayFrame_Number and *DisplayFrame_PerRow, converts those to byte offsets with DisplayFrame_CalculateOffset, and copies *DisplayFrame_Height character rows of *DisplayFrame_LineWidth bytes from the buffer to the screen at *DisplayFrame_Column / *DisplayFrame_Row. It then copies the matching attributes from the buffer (offset by 1800) to the attribute file.

The values in the snapshot describe rows of 04 frames of 08 by 0A characters, copied to column 19 row 03 after line 60.

Copies one frame of the picture held in the buffer at PictureBuffer to the screen: first the pixel rows, then the attributes from PictureBuffer_Attributes. Called by BASIC as "ins" (FB09) with the frame number POKEd into DisplayFrame_Number. The routine works out the frame's row and column in the sheet from DisplayFrame_Number and DisplayFrame_PerRow, converts those to byte offsets with DisplayFrame_CalculateOffset, and copies DisplayFrame_Height character rows of DisplayFrame_LineWidth bytes from the buffer to the screen at DisplayFrame_Column / DisplayFrame_Row. It then copies the matching attributes from the buffer (offset by 1800) to the attribute file. The values in the snapshot describe rows of 04 frames of 08 by 0A characters, copied to column 19 row 03 after line 60.
DisplayFrame	FB09	DI	Disable interrupts.
	FB0A	LD ($FF76),SP
	FB0E	LD SP,$FFBE
	FB11	LD A,($FB03)
	FB14	LD B,A
	FB15	LD C,$01
	FB17	LD A,($FB02)
	FB1A	DEC A
DisplayFrame_0	FB1B	CP B
	FB1C	JR C,DisplayFrame_1
	FB1E	SUB B
	FB1F	INC C
	FB20	JR DisplayFrame_0
DisplayFrame_1	FB22	INC A
	FB23	LD B,A
	FB24	LD HL,$FB04
	FB27	XOR A
	FB28	DEC B
	FB29	JR Z,DisplayFrame_3
DisplayFrame_2	FB2B	ADD A,(HL)
	FB2C	DJNZ DisplayFrame_2
DisplayFrame_3	FB2E	LD B,C
	FB2F	LD C,A
	FB30	LD HL,$FB05
	FB33	XOR A
	FB34	DEC B
	FB35	JR Z,DisplayFrame_5
DisplayFrame_4	FB37	ADD A,(HL)
	FB38	DJNZ DisplayFrame_4
DisplayFrame_5	FB3A	LD L,A
	FB3B	CALL DisplayFrame_CalculateOffset
	FB3E	LD ($FBC5),HL
	FB41	SLA H
	FB43	SLA H
	FB45	SLA H
	FB47	LD BC,($FB00)
	FB4B	ADD HL,BC
	FB4C	EX DE,HL
	FB4D	LD A,($FB07)
	FB50	LD L,A
	FB51	LD A,($FB06)
	FB54	LD C,A
	FB55	CALL DisplayFrame_CalculateOffset
	FB58	LD ($FBC3),HL
	FB5B	SLA H
	FB5D	SLA H
	FB5F	SLA H
	FB61	LD BC,$4000
	FB64	ADD HL,BC
	FB65	EX DE,HL
	FB66	LD A,($FB05)
	FB69	LD B,A
DisplayFrame_6	FB6A	PUSH BC
	FB6B	LD B,$00
DisplayFrame_7	FB6D	LD A,($FB08)
	FB70	LD C,A
	FB71	PUSH HL
	FB72	PUSH DE
	FB73	LDIR
	FB75	POP DE
	FB76	POP HL
	FB77	CALL ScrollWindow_NextLine
	FB7A	EX DE,HL
	FB7B	CALL ScrollWindow_NextLine
	FB7E	EX DE,HL
	FB7F	JR NZ,DisplayFrame_7
	FB81	POP BC
	FB82	DJNZ DisplayFrame_6
	FB84	LD HL,($FBC5)
	FB87	LD BC,($FB00)
	FB8B	ADD HL,BC
	FB8C	LD BC,$1800
	FB8F	ADD HL,BC
	FB90	EX DE,HL
	FB91	LD HL,($FBC3)
	FB94	LD BC,$5800
	FB97	ADD HL,BC
	FB98	EX DE,HL
	FB99	LD A,($FB05)
	FB9C	LD IYl,A
	FB9E	LD B,$00
DisplayFrame_8	FBA0	LD A,($FB08)
	FBA3	LD C,A
	FBA4	PUSH HL
	FBA5	PUSH DE
	FBA6	LDIR
	FBA8	POP DE
	FBA9	POP HL
	FBAA	LD C,$20
	FBAC	ADD HL,BC
	FBAD	EX DE,HL
	FBAE	ADD HL,BC
	FBAF	EX DE,HL
	FBB0	DEC IYl
	FBB2	JR NZ,DisplayFrame_8
	FBB4	LD SP,($FF76)
	FBB8	RET