[Linux-fbdev-devel] Re: fbdev, console, (video) overlay/underlay & fbtv

[Romain D. <do...@ir...>]

Gerd Knorr wrote:

> Better use the _IOR / _IOW / _IOWR macros.

ATM FB doesn't use them, so I picked up a bunch of value
in sequence.

> > #define FB_VIDOVERLAY_PIXELTYPE_CI8     0x0020
> 
> What is this one?

ColorIndexed 8bpp. Could be used for still overlay
(i.e. a big Penguin as background picture :-)

> > #define FB_VIDOVERLAY_PIXELTYPE_YUV422  0x0040
> > #define FB_VIDOVERLAY_PIXELTYPE_YUV444  0x0080
> 
> packed pixel or planar?  yuv420 should be there too, mpeg decompressed
> gives you planar yuv420.

Packed Pixel was in my mind. I'll add the other.
(the pm3 doesn't have YUV420 :-( )

> I'd pass pixeltype + width + height here and let the driver calculate +
> return the image size and scanline length.  The driver can easily take
> care about alignment and related issues then.

The idea was the App could allow an arbitrary buffer and
do whatever it pleases in it, including somthing entirely
different from overlay. It might be useful if one
add a in-FB-memory copy IOCTL or API.

Also I though that the only overlay-related info
would be put in FBIOPUT_VIDOVERLAY_START, and
never stored in the driver (except for buffer
data), only in the app.

> n_over == -1  =>  "give me any free one" ?

good idea.

> >       __u16 blend_factor;             /* blending factor */
> 
> add chroma key (rage) here ?

The problem is, how to handle the mix between the overlay
and the console layer. If the FB doesn't have an alpha
channel (CI8, RGB565), one must use a color key. So one
must be able to know which color this is for FBCON.
If there _is_ an alpha channel and we wish to use it,
we must define how to handle the alpha in the fbcon
layer: if it is cleared or not when clearing the screen,
what happen when FBCON draw a character (cleared,
set, set only on the background...) ans so on.

So I simply dodged the problem by saying, we display
the overlay in its area blended (0 to 100%) with
the current display. But we need a better way,
obviously.

-- 
DOLBEAU Romain               | l'histoire est entierement vraie, puisque
ENS Cachan / Ker Lann        |     je l'ai imaginee d'un bout a l'autre
do...@ir...             |           -- Boris Vian