The Journalist's Cage

A Screenshot Utility Is Born

GNOME's built-in screenshot utility really sucks. It must be invoked every time a single screenshot is taken, the interface doesn't facilitate capture of specific windows or screen regions, there is no easy way to save the same capture to more than one location, and the tiny preview makes it difficult to evaluate the captured image before I choose to save it. When I need to make screenshots for my articles, I typically use the import command provided by ImageMagick. I finally got tired of putting up with suboptimal screen capture tools and decided to write my own.

My new screenshot utility features a full-size preview, the ability to capture individual windows or specific screen regions, an integrated file selection component, support for saving the captured image directly to a remote location, and support for saving the same capture to multiple locations. The entire utility took me about an hour to build, including time spent researching the various APIs. The current version is approximately 25 lines code, not including comments or blank lines. I designed the interface with Glade and wrote the code with Ruby. The network transparency features are all implemented with GNOME's VFS library and the screen capture functionality is provided by Ruby ImageMagick bindings.

The effectiveness of my utility, the relative ease with which I developed it, and the brevity of the code are all a testement to the power of Ruby and GNOME. I'm convinced that Ruby and Glade provide the best solution available for rapid application development on Linux. The GNOME bindings for Ruby are excellent and relatively complete, but there are still problems in a few places. The GnomeVFS bindings are currently undocumented, and the API does not behave the way one would expect it to. GnomeVFS::File diverges from the traditional File class in several respects. The most frustrating difference relates to file creation. It should be possible to create a new remote file thusly:

GnomeVFS::File.new("sftp://cixar.com/home/segphault/test.txt", 2)

Unfortunately, the above yields a "File not found" error. I queried the folks in the relevant IRC channel, but didn't get much help. After a great deal of experimentation, I filed a bug report. I then proceeded to examine the relevant source code to see if I could find out why file creation was raising a "File not found" error. Careful examination of the file_initialize function revealed that file creation only transpires when the File.new method is passed three arguments. The missing argument indicates whether or not the program should refuse to overwrite existing files. The following successfully performs the creation operation:

GnomeVFS::File.new("sftp://cixar.com/home/segphault/test.txt", 2, false)

In any event, my new utility works quite well, and you can benefit from it too, because I am distributing it under the GPL. You can read the code or download the utility. Keep in mind that it has quite a few dependencies, so you might not be able to run it if you can't get the necessary libraries.

Tags: ruby, programming, imagemagick, gnome, glade

Posted on 2005-08-241 comments