[ale] fvwm and Mozilla

[Joseph Knapka]

Subba Rao <subba9 at cablespeed.com> writes:

> Hello again,
> 
> It is about fvwm again.  When I open some applications (particularly Mozilla,
> Netscape, GThumb) my wallpaper and the application do change into some
> psychdelic backgrounds.  Each time the mouse focus moves from the application
> to the desktop or vice versa, the colors get swapped.  I do not have any
> problems apps such as Acrobat or OpenOffice etc.  They are working fine.
> 
> Has anyone seen this behaviour before?  How do I fix these color changes in
> display?

I'm not an expert on this stuff, so someone correct me if
necessary...

You must first understand that the color scheme of your desktop
(its "visual") may be one of two different types:

  * RGB: the value of each pixel is an RGB representation of the
desired color. For a 24-bit TrueColor display, you have 8 bits to
specify red, 8 bits for green, and 8 bits for blue.

  * Palettized: the value of each pixel is an index into a table of
RGB values. In this case, the pixel values themselves are unrelated to
the actual colors. Palettized visuals are typically used for low bit
depths like 4 or 8 bits - your video hardware supports millions of
colors, but the palette allows you to use only 16 or 256 of them at a
time. Usually the palette actually lives in the video card's memory,
and when you change the values in the palette it immediately affects
the displayed colors. X permits applications to install their own
palettes, and it keeps track of which one to use for each app (when
that app has focus). This is the root of your problem.

What's happening is that you're using a palletized visual, and those
"problem" applications are installing private palettes (also called
"color maps"). So everytime Mozilla gets focus, for example, it
changes the 256 colors the video hardware is using to a *different*
256 colors, which causes Mozilla to look right, but the desktop to
look funny.

There are two possible solutions:

(1) Instruct each troublesome application not to use a private color map.
You'll have to check the docs (if any); I'm pretty sure Mozilla has
a command-line option (or maybe an X resource) that controls this, but
I may be wrong. When you do this, the apps might look weird, because
the colors they want to use may not be available in the global color
map.

(2) The better option is to use a genuine RGB color depth on your
display. 16 bit color or better should use RGB pixel values.

Cheers,

-- Joe

> Thank you in advance.
> 
> --
> Subba Rao
> subba9 at cablespeed.com
> ------------------------------------------------------------------------------
> Old American Wild West saying:       God created men but Colt made them equal.
> Today:                  Linus created Linux and Linux made IT companies equal.
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