[CREATE] OpenRaster needs preview

[Martin Renold]

hello,

Here are my notes and the proposal.
I will add this to the specification if noone objects.

Notes:

This is what other file formats do:
- OpenOffice: includes Thumbnails/thumbnail.png, 256x256, alpha
- Krita: includes preview.png, 256x256
- XCF: GIMP adds an 128x128 preview to ~/.thumbnails/normal/
  Nautilus and Konqueror use them but can't generate them.
  Renaming or moving those files removes the preview, see:
  http://jens.triq.net/thumbnail-spec/thumbsave.html

The maximum size that any program shows without "really" opening the
image is 256x256 (when hovering over PNG in konqueror).  Usually,
thumbnails and previews are limited to 128x128 at maximum zoom.

Proposal:

I suggest we go the Krita way and add a file called "preview.png", with a
maximum size of 256x256.  The preview must not be referenced in stack.xml. 
The preview is highly reccommended, but not mandatory.  This is in order to
simplify the minimal OpenRaster export implementation.

Programs that save OpenRaster files should add a scaled version of the
preview to ~/.thumbnails/normal as specified by the "Thumbnail Managing
Standard" (max. 128x128, see link above).  Other programs are encouraged to
update this when required (eg. file rename).

bye,
Martin