Jon Smirl wrote:

I'm trying to work out a syntax for the sysfs attribute that will
control the config. My first idea is to use a alpha/red/blue/green
syntax. When red is set and blue/green are missing index mode is set.
When green is set and red/blue are missing gray scale is set.

No, if r.offset = g.offset = b.offset = 0 and
r.len = g.len = b.len = n, then set index mode (pseudocolor).  For grayscale,
check if var.grayscale is set.

Are there chips that can scanout from buffers not packed at a power of two?

Yes, rgb888 (Intel 810).

How should I work different color spaces (YCbCr) into this?

Create a new visual FB_VISUAL_YUV, then treat rgb as yuv.

4bpp Index = /4
4bpp greyscale = //4
8bpp Index = /8
8bpp RGB 332 = /3/3/2
8bpp greyscale = //8
16bpp aRGB 1555 = 1/5/5/5
16bpp RGB 565 = /5/6/5
16bpp aRGB 4444 = 4/4/4/4
16bpp aIndex 88 = 8/8
24bpp RGB 888 = /8/8/8
24bpp aRGB 6666 = 6/6/6/6
32bpp aRGB 8888 = 8/8/8/8
32bpp aRGB 2:10:10:10 = 2/10/10/10

How are these packed?

How each pixel is packed in the framebuffer is determined by bpp.
How each color component is packed within the pixel is determined by
{red|green|blue|transp}.{offset|len} 

1 bpp monochrome (black = 0 and white = 1 or vice versa)
1 bpp indexed
2 bpp indexed
3 bpp indexed
5 bpp indexed
6 bpp indexed
7 bpp indexed

These would have the same config, //8, right? You then just control

No, packing is determined by bpp. So 7bpp has 7 bits per pixel.  However
a color depth of 7 with bpp8 has 8 bits per pixel but only 7 significant bits.

what you write to the byte.
8 bpp monochrome (black is all zeroes and white is all ones or vice versa)
8 bpp greyscale

How does this work, is one 24 bit color the key?
32 bpp indexed+RGB 888 with color key to enable RGB888

This is directcolor. Each component is indexed.


Tony


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