showimage+: a slightly improved derivative of SDL_image's showimage
By Matthew Boeh (mboeh@desperance.net)

This was a utility image viewer I made in 2005, designed because at the time none of the image
viewers available for X11 both (a) had the simplicity of controls I wanted and (b) worked
acceptably with a tiled window manager (Ion, at the time).

YMMV, caveat emptor, anno domini, etc. but I still use it to this very day because it's lightweight
and does exactly what I want it to. The actually tricky parts of the code come from a SDL_image
example program. I just built around it.

You'll need libsdl and SDL_image development packages. On Ubuntu:

$ sudo apt-get install libsdl1.2-dev libsdl-image1.2-dev

Controls:
- Left, Right: Go backward or forward through the list of images.
- number: Type a number and hit left or right to step through that many images.
- Up, Down, comma, period: Pan up, down, left, or right over an image.
- Home, End: Go to the first or last image.
- Delete: Remove this image from the list.
- Tab: Switch the background on which transparent images are drawn to: checkered, black, white.
- c: clear the memory cache.

Changes:
1.4.6:
* You can now click and drag on the image to pan.
1.4.5:
* Added alpha control and the option for white or black backgrounds.
1.4.4:
* Some cleanup.
1.4.3:
* Boundary checks: going back from the first or forward from the last is now a no-op.
1.4.2:
* Removed a few bugs:
  - wouldn't respond to 'quit' signal
  - crashed on non-loadable images
1.4
* Faster loading and navigation of images.
* Fast-forwarding through images -- type a number and press left or right to go
  that many images back or forward.
1.3
* Viewport now automatically resizes with window.
1.2
* A sizeable viewport (-h and -w options) that can be scrolled (up and down, comma and period)