Makes the thumbnails square:

Makes the window fit the image when displaying single image:

Makes sxiv derive the thumbnail type from the image so sxiv can support transparent thumbnails:

adds the ability to cycle when viewing multiple images

old version of sxiv-square-thumbnails.patch
last working commit is b2dbd2f

Ruby script for finding optimal thumbnail size.
The thumbnail size is calculated so that when viewing thumbnails in full screen the empty space is minimal.

The calculation uses the width and height of the display.
If you are using the bottom bar you have to substract his height(by default the font size + 2px) from the height of the display.

The calculation can be done for windows too.

sxiv.rb -w <window-width> -h <window-height>

For more information:

sxiv.rb --help