Learning Perl/Tk

12.4. Colormap Complications

When you are running several applications at once and you start a web browser, you'll sometimes notice that the colors become corrupted. When you switch from an application to the browser, the colors in your other applications suddenly change. If you switch back from your browser to an application, the browser colors change. This is happening because the web browser is a color hog. It has requested more colors than the operating system can allocate at once. The OS must alter the colormap between applications to allow the active application to use the colors it wants to use. The colormap simply gives the operating system a way to keep track of who is using which colors.

Perl/Tk applications can have many colors too—you can get color-happy and make each button a different color of the rainbow. This can cause problems if there are other applications running that want a lot of different colors too. If other applications are color hogs, Perl/Tk will switch to black-and-white mode. If you don't like this behavior, you can use the -colormap option to override it. -colormap takes either the word "new" or a reference to another window. If given "new", it will create its own colormap. When you use -colormap with another window, the two windows will share the colormap. But there is one catch, and that is the -visual option.

The -visual option takes as an argument a string that contains a keyword and a number; for example:

-visual => "staticgrey 2"

The keyword ...