Re: [gentoo-user] New HD monitor stretches everything. How to teach Xorg?

[Walter Dnes]

On Wed, Aug 25, 2010 at 01:29:29PM -0700, Kevin O'Gorman wrote

> There are some confusing things about this.
> -  The log contains 1920x1080 modelines, but is not using them or
> clearly stating the reason.
> -  The log contains the lines
>       (!!) MACH64(0): Virtual resolutions will be limited to 8191 kB
>       due to linear aperture size and/or placement of hardware cursor
>       image area.

  1920x1080 uses how many pixels?
$ echo $(( 1920 * 1080 ))
2073600

  The programmers writing X drivers use ***FOUR*** bytes per pixel for
24-bit colour.  This is due to double-word addressing being *MUCH*
easier and faster than sliding groups of 3 bytes per pixel.  This means
that to support 1920x1080 at 24 bits requires how many Kbytes...

$ echo $(( 1920 * 1080 * 4 / 1024 ))
8100

  It'll just barely squeeze in a 1920x1080 image, but forget about
acceleration or backing store, because there's almost no spare memory.
What you might want to try is forcing 16-bit colour, which would use
half the memory.  See http://www.gentoo.org/doc/en/xorg-config.xml

  The magic option is DefaultDepth.  You would want something like so,
the identifiers changed to match your setup...

Section "Screen"
  Identifier  "Default Screen"
  Device    "RadeonHD 4550"
  Monitor   "Generic Monitor"
  DefaultDepth  16
  # Skipping some text to improve readability
  SubSection "Display"
    Depth   16
    Modes   "1920x1080"
  EndSubSection
EndSection

  When viewing hi-res colour images, you may see some banding due to
the limited colourspace (64 K colours instead of 16 million), but it may
offer full pixel resolution, and the banding may not be noticable most
of the time.

-- 
Walter Dnes <waltdnes@××××××××.org>