VICKY

VICKY - the graphics engine

"Vicky" is the name of the graphics engine of the C256 Foenix. It supports:

• 640x480@60FPS Max Resolution @ 256 Colors (1 Byte per pixel)
• 32 Sprites with a resolution of 32x32 pixels
• 4 layers of tiles with a resolution of 16x16 pixels for each tile
• Text Mode

During the video layer composition, Vicky has to read 1 line of bitmap (640 pixels), 1 line of tiles for each layer (4x 640 pixels) and all the lines that are part of the 32 Sprites (worst case scenario 32 lines of 32 pixels), that are displayed on that line. Then a composition and priority encoding is done. In order to establish a priority, in other words, to know which pixel will be in front, Vicky needs to store 10 lines of 640 pixels then scan the lot and determine which one will be displayed.

640 + 640 + 640 + 640 + 640 + (32 * 32) = 4224 Pixels are to be read during a single line interval. The pixel rate is 200Mbytes/sec, 5ns, so the overall operation takes 21.12us, without calculating the overhead in the FPGA to go from one process to the other.

The pixel value $00 is always transparant and the assigned value to a transparant pixel is automaticly the background color. Despite the fact that there is an ALPHA value, it is not supported.

Modes

Modes are enabled and disabled via the Vicky Master Control Register at $AF0000 via the control bits:

Mstr_Ctrl_Text_Mode_En	= $01	Enable the Text Mode
Mstr_Ctrl_Text_Overlay	= $02	Enable the Overlay of the text mode on top of Graphic Mode (the Background Color is ignored)
Mstr_Ctrl_Graph_Mode_En	= $04	Enable the Graphic Mode
Mstr_Ctrl_Bitmap_En	= $08	Enable the Bitmap Module In Vicky
Mstr_Ctrl_TileMap_En	= $10	Enable the Tile Module in Vicky
Mstr_Ctrl_Sprite_En	= $20	Enable the Sprite Module in Vicky
Mstr_Ctrl_GAMMA_En	= $40	Enable the GAMMA correction - The Analog and DVI have different color values, the GAMMA is great to correct the difference
Mstr_Ctrl_Disable_Vid	= $80	This will disable the Scanning of the Video hence giving 100% bandwith to the CPU

Bitmap Layer

The bitmap is stored anywhere in $B0 bank memory. If the bitmap is supposed to start at $B0:0000, the BM_START_ADDY has to be set to $00:0000.

• BM_CONTROL_REG = $AF0140 (Bit[0] - Enable, Bit[3:1] - LUT Select)
• BM_START_ADDY_L = $AF0141
• BM_START_ADDY_M = $AF0142
• BM_START_ADDY_H = $AF0143

LUT

A LUT, namely a Look-Up-Table, stores a selection of colors. 256 colors are supported in the video composition, which are selectable out of 16.777.216 colors in the 24 Bit RGB color scheme. The LUT also contains an 8 Bit alpha channel, though it isn't supported. In summary, the LUT has $400 (1024) bytes - and the order for composing it is R value -> G value -> B value -> A value.

As an example, if you would want to compose a LUT with the original 16 C64 VIC colors, it would look like this:

Address	Hex Values	Decimal RGB Value
$AF:2000	000000	0, 0, 0
$AF:2004	FFFFFF	255, 255, 255
$AF:2008	880000	136, 0, 0
$AF:200C	AAFFEE	170, 255, 238
$AF:2010	CC44CC	204, 68, 204
$AF:2014	00CC55	0, 204, 85
$AF:2018	0000AA	0, 0, 170
$AF:201C	EEEE77	238, 238, 119
$AF:2020	DD8855	221, 136, 85
$AF:2024	664400	102, 68, 0
$AF:2028	FF7777	255, 119, 119
$AF:202C	333333	51, 51, 51
$AF:2030	777777	119, 119, 119
$AF:2034	AAFF66	170, 255, 102
$AF:2038	0088FF	0, 136, 255
$AF:203C	BBBBBB	187, 187, 187