Please improve/clarify the Icon Theme Specification

[Pascal De Vuyst]

Please clarify the Icon Theme Specification for the points mentioned below.

Please mention that "Directories" are searched from left to right for
first match. The same applies for Inherits. This is not clear now.

Clarify what Type=Threshold means.

If I understand correctly this is used to match icon sizes that differ
plus or minus the Threshold value from the requested size.

This is best illustrated with the KDE versus GNOME menu icons.
GNOME uses 24x24 pixel menu icons and KDE 22x22 pixel menu icons.
Let's say we have a KDE icon theme with 22x22/apps icons that would be
used in GNOME. For the 22x22/apps directory Type=Treshold is set with
the default Treshold value of 2 pixels. This icon directory would match
the requested size of 24 pixels for the GNOME menu. It is not clear in
the current specification how the implementation would handle the 22x22
to 24x24 pixel transformation. The best way would be to add a 1px
transparant padding border around the 22x22 icon creating a 24x24 icon
(this is also suggested by tango project). The current implementation
for GNOME seems to upscale the 22x22 icon to 24x24, this makes the icon
look very blurry. I think the padding is a better solution and this
should be suggested in the specification.

Now look at the other side and say we have a GNOME icon theme with
24x24/apps icons that would be used in KDE. For the 24x24/apps directory
Type=Treshold is set with the default Treshold value of 2 pixels. This
icon directory would match the requested size of 22 pixels for KDE menu.
It is not clear in the current specification how the implementation
would handle the 24x24 to 22x22 pixel transformation. Most icons have
some free space around the icon, the best way would be to remove a 1px
border from the 24x24 icon creating a 22x22 icon (clipping). If the
icons don't have enough free space for clipping it, it should be
downscaled to 22x22 pixels. This should be suggested in the specification.

Please mention that the Threshold value is in pixel size, in the current
explanation you could think it is some kind of scaling factor.

Context=Applications is listed under section Example but not described
under section Context. It would be better to refer to the Contexts and 
directory names described in the Icon Naming Specification or include 
this also in the Theme Specification. The directory structure should be 
part of the Icon Theme Specification.

The current specification suggests that 3rd party application icons
should be in the hicolor fallback theme.
I have the following issue related to this:
Currently I have gnome installed with some extra KDE apps. By installing
the KDE apps the default KDE icon theme (crystalsvg) is also installed.
The standard theme inherit order used by GNOME seems to be:
Inherits=default.gnome,default.kde,hicolor. Use of default.kde makes
sense since we want to see the KDE icons for the installed KDE apps.
Now the problem is default.kde contains icons for third party
applications, e.g. gaim. This means that when I select for instance the
Tango icon theme that doesn't have an gaim icon, it falls back to the
default.kde icon for gaim. This is unexpected, I would expect to see the
gaim icon from hicolor fallback theme in my GNOME installation.
Changing the standard theme inherit order for GNOME to:
Inherits=default.gnome,hicolor,default.kde,default.xfce would solve this
problem. According to the icon theme specification hicolor should always
be the last fallback theme, these multi desktop environment issues
should be adressed in the icon theme specification.

Some remarks about hicolor icon theme.

The specification doesn't say anything about the use of Type=Scalable
for bitmap icons it only suggests at least a 48x48 png icon. A 48x48 png
icon could be provided for an application and Type=Scalable in
combination with MinSize and MaxSize would allow this icon to be scaled
down. For the hicolor fallback theme this would be enough.

Therefore /usr/share/icons/hicolor/index.theme should be changed to
contain the following:

[bitmap/48x48/apps]
Size=48
Type=Scalable
MinSize=16
MaxSize=48

This will make 48x48 png application icons downscalable to 16x16 pixels
for window list icons, to 24x24 for GNOME menus and panel icons and to
22x22 for KDE.
There is no need to provide 16x16, 22x22 or 24x24 versions in the theme
when they are just downscales of the 48x48 icon, the downscaling could
be done by the implementation and gives the same result.

Currently if I look in hicolor icon theme scalable/apps directory in my
GNOME distribution I see some 3rd party applications provide svg with
48x48 nominal size and other svg with 128x128 nominal size.
The problem with this is that 48x48 icons appear to small on the desktop
because of the wrong Size=128 indication.

To address this I think the (sub)directory structure should be changed to:
<icon type>/<nominal size>/<category>/<subcategory>

<icon type> = "bitmap" for png/xpm or "scalable" for svg/svgz.
<nominal size> = nominal size of png/pxm or svg in format width x height
without spaces, e.g. 48x48.
<category> = apps, filesystems, ...

The <nominal size> indication will make it easier for people to respect
the nominal size for icons in the directory and therefore will avoid
wrong scaling on the desktop.
The (sub)directory structure would make the Size key optional since the
size can be found in the <nominal size> subdirectory name.

As example, this should be included in hicolor icon theme:

[scalable/48x48/apps]
Size=48
Type=Scalable
MinSize=16
MaxSize=256

[scalable/128x128/apps]
Size=128
Type=Scalable
MinSize=16
MaxSize=256

Thanks in advance,
Pascal De Vuyst