Re: fixing fbdev for various framebuffer configs

[Jon Smirl <jonsmirl@gmail.com>]

On 7/29/05, Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> On Fri, 29 Jul 2005, Jon Smirl wrote:
> > On 7/29/05, Antonino A. Daplas <adaplas@gmail.com> wrote:
> > > Jon Smirl wrote:
> > > > It has been determined that bits per pixel is insuffucient to
> > > > enumerate all the needed fbconfigs. Here are the possible fgconfigs
> > > > from the OpenGL headers:
> > > >
> > > > total bits
> > > > 8     GL_R3_G3_B2
> > > > 8     GL_RGBA2
> > > > 12   GL_RGB4
> > > > 15   GL_RGB5
> > > > 16   GL_R5_G6_B5
> > > > 16   GL_RGBA4
> > > > 16   GL_RGB5_A1
> > > > 24   GL_RGB8
> > > > 30   GL_RGB10
> > > > 32   GL_RGBA8
> > > > 32   GL_RGB10_A2
> > > > 36   GL_RGB12
> > > > 48   GL_RGB16
> > > > 48   GL_RGBA12
> > > > 48   GL_FLOAT_RGB16
> > > > 64   GL_RGBA16
> > > > 64   GL_FLOAT_RGBA16
> > > > 96   GL_FLOAT_RGB32
> > > > 128 GL_FLOAT_RGBA32
> > > >
> > > > We need to be able to set any of these through the fbdev interface. We
> > > > also need to allow for possible future expansion.
> > >
> > > To set for example, RGBA16, set {transp|green|red|blue}.len to 16, the
> > > offsets to 0, 16, 32, 48, and bits_per_pixel to 64.  Then let the driver
> > > sort it out.  I don't know what we can do about the FLOAT formats...
> > >
> > > >
> > > > Ideas on how to adjust the fbdev interface?
> > >
> > > Well, no need to adjust the interface.  But it is limited though to
> > > 16 bits per channel.  Redefining them to 32 will break a lot of apps.
> 
> It's only the colormap entries that are limited to 16 bits per color component,
> right? The color components in pixel values can be much larger (up to 2^31 bits
> :-).
> 
> > My current idea is to get rid of the bit_per_pixel attribute and
> > replace it with config. Config would take strings like 8,8,8 or
> > 5,5,5,1 or 32.,32.,32.
> 
> That's not acceptable. How do you differentiate between RGB888 (without alpha)
> using 24 or 32 bits per pixel?

Isn't that the driver's problem? You can't differentiate using OpenGL.
This does imply that I need a read only bits_per_pixel to allow apps
to caculate the stride.

> Or more general, what with hardware that has unused bits in its pixel values,
> e.g. hardware that has 8 bits per pixel but uses only 1 bit per byte in
> monochrome mode and 4 bits in 16-color mode?
> 
> > > > What is the effect of alpha bits on the scanout buffer, do they do anything?
> > >
> > > I think if there is another layer such as an overlay, the alpha bits can
> > > control the transparency between the framebuffer and the overlay. If only
> > > the framebuffer is active,  I don't believe it has any effects.
> 
> It has on e.g. Set Top Box hardware.
> 
> Gr{oetje,eeting}s,
> 
>                                                 Geert
> 
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
> 
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                                             -- Linus Torvalds
> 
> 
> -------------------------------------------------------
> SF.Net email is Sponsored by the Better Software Conference & EXPO September
> 19-22, 2005 * San Francisco, CA * Development Lifecycle Practices
> Agile & Plan-Driven Development * Managing Projects & Teams * Testing & QA
> Security * Process Improvement & Measurement * http://www.sqe.com/bsce5sf
> _______________________________________________
> Linux-fbdev-devel mailing list
> Linux-fbdev-devel@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/linux-fbdev-devel
> 


-- 
Jon Smirl
jonsmirl@gmail.com


-------------------------------------------------------
SF.Net email is Sponsored by the Better Software Conference & EXPO September
19-22, 2005 * San Francisco, CA * Development Lifecycle Practices
Agile & Plan-Driven Development * Managing Projects & Teams * Testing & QA
Security * Process Improvement & Measurement * http://www.sqe.com/bsce5sf