; HGFX chunky - video settings for a classic bitmap manipulation
;
; Before video-buffers access and paging,
; once and for all initialize videosystem settings
;
; set HGFX graphics
;
	ld bc,0x7C3B	; ZXi general port0
	ld a,1			; g_zxi_001 - Extra graphics modes
	out (c),a
	inc b			; ZXi general port1
	ld a,3			; 512*384 resolution, 16 colours
	out (c),a
;
	dec b			; ZXi general port0
	ld a,2			; g_zxi_002 - Advanced video
	out (c),a
	inc	b			; ZXi general port1
	xor a			; bit 1 = 0 	BigBorder off
	out (c),a
;
	dec b			; ZXi general port0
	ld a,0x20		; g_zxi_020 - HGFX general settings
	out (c),a
	inc	b			; ZXi general port1
	ld a,7			; 10000111
;	
; bit0 = 1	linear memory
; bit1 = 1	indexed (index 0-7) border colour
; bit2 = 1	ZX screen transparency disable
; bit7 = 0  enable write to HGFX (incl. registers & colour table)	
;
	out (c),a
;
;
; videoRAM address at 0xC000
; that is a "window" of a zx-screen size (6144 bytes),
; not used with chunky BRAM, just for planar operations only
; a change of one bit affects the whole pixel stored in the video-buffer
; 
;
	dec b			; ZXi general port0
	ld a,1			; g_zxi_021 - high byte of VideoRAM
	out (c),a
	inc b			; ZXi general port1
	ld a,0xC0		
	out (c),a		; beginning at 0xC000
;
; address of the HGFX colour table RAM at 0xD800
;
	dec b			; ZXi general port0
	ld a,1			; g_zxi_023 - high byte of colour table
	out (c),a
	inc b			; ZXi general port1
	ld a,0xD8		
	out (c),a		; at the place after above VideoRAM
;
; indexed colours are defined in TrueColour BGR 
; HGFX mode 3 provides 16 colours only,
; this takes a colour table of 3*16 bytes 
;
;
; start address of the HGFX registers at 0xD900
;
	dec b			; ZXi general port0
	ld a,1			; g_zxi_022 - high byte of Registers Area
	out (c),a
	inc b			; ZXi general port1
	ld a,0xD9		
	out (c),a
;
;
; Now is the videosystem configured.
;
;
; The HGFX RAM uses its own memory, 1 or 2 video-buffers.
; Two ways exist how to access the buffer(s):
;	- planar:	changing a bit in the HGFX videoRAM
;				affects a whole (coloured) HGFX pixel
;	- chunky:	8K or 16K part of the buffer is paged to one
;				of eight Areas /four Zones
;

; Because we are starting to use a direct access to chunky BRAM
; (HGFX buffers) at first, we should disable a write-enable
; to HGFX (planar) bitmap, regs and col.table
; 
	dec b			; ZXi general port0
	ld a,0x20		; g_zxi_020 - HGFX general settings
	out (c),a
	inc	b			; ZXi general port1
	ld a,135		; access to VideoRAM disabled - bit 7 is on
	out (c),a
;
;
; Parts of the video-buffer are accessible per X&Y coordinates,
; with OFFSETs. Having HGFX registers at 0x5B00, there is:
;
;	0x5B07 (2 bytes)	OffsetY 		0 ... 383
;
; Note: With chunky graphics, only OffsetY is used.
;		In planar we work with both X&Y offsets (quick and easy way,
;		to print a text, point an arrow, etc. with a coordinates)
;
; Next HGFX register usable for chunky operations
; is PLANARMASK, basically filled with a value 255
;
;	0x5B04 (1 byte)		PlanarMask
;
; --------------------------------------------------------------------------
;
; HGFX (chunky) video-buffer access
;
; choose 16K segment - Memory Zone	
	ld a,3			; Zone 2	0xC000 - 0xFFFF	
	out (0x73),a	; set Zone

; choose 16K HGFX chunky - both Areas are HGFX,
; so set Zone memory layout for this
;
	ld a,131	; 10000011
				; bit0  = enable write Area0
				; bit1  = enable write Area1
				; bit4-7 = memory type, value 8 = HGFX Area0 & HGFX Area1
	out (0x53),a	

; Please note the HGFX video-buffers are not addressed in a classical way, 
; but through a start-of-line (OffsetY) value.
; Example:
;   
; Having a HGFX chunky Areas from 0xC000,
; willing to get an access from the first third of the 512*384 screen,
; so the first byte of the line no. 128 starts at 0xC000
;
	ld hl,128
	ld (0x5B05),hl		; set OffsetY to 128
		
; 512*384 is a 16colour-mode, one byte holds two pixels.
; One line takes 256 bytes, the whole video-buffer has 98304 bytes.
; With OffsetY = 128 you will get an access to 64 screen lines from
; 128 to 191 (from video-buffer part, addr. 32768 to 49151) in 16KB Zone.
;

; --------------------------------------------------------------------------
;
; Chunky vs. Planar comparison: example of 'software' pointer
;
; Decide, what type of screen data manipulation is good for.
; Example: mouse pointer, size 8x16 px, 4 colors 
;
; In general, we need to pick up data, make a test for transparency,
; write, then shift to a new pixel... in the classical (HGFX chunky)
; bitmap all this covers 128 bytes and one byte manipulation takes
; approx. 24 tacts, 3000 tacts in total?
;	
; A faster method is writing 48 bytes through Planar (32B data, 16B mask)
; such a painting of a pointer takes about 100 clock cycles at 3.5 MHz		
; However, when saving background bytes (behind the pointer), it is better
; to deal with a chunky area, in combination with the FastDMA
; 

; --------------------------------------------------------------------------
;
; Notes on the Direct Memory Access using the FDMA
;
; The Z80-CPU is stopped when the FastDMA is doing jobs.
; At a speed of 3.5 MHz, the transmission of 1 byte takes about 0.48 tact.
;