Mastering Perl/Tk

Displaying an Image or Bitmap

The simplest way to replace the text on your Button with an image is to use a bitmap.^[1] The image will take the place of the text; you can’t display both at the same time. The -bitmap option takes a string that specifies which bitmap to use:

-bitmap => 'bitmapname'

There are several built-in bitmaps: error, gray12, gray25, gray50, gray75, hourglass, info, questhead, question, warning, Tk, and transparent. Figure 4-7 shows all the built-in bitmaps. To more easily show you the bitmaps, Figure 4-7 was grabbed from the widget demonstration program.

Using -bitmap for a Label is exactly the same as for a Button. You’ll notice that the Tk bitmap is the same as that used in the upper-left corner of the application. Here are some examples using -bitmap when creating a Button:

$mw->Button(-bitmap => 'error', -command => \&handle_error)->pack;

To specify a bitmap from a file, you need to put an @ in front of the path:

$mw->Button(-bitmap => '@/usr/nwalsh/mybitmap', 
             -command => sub { exit })->pack;

Note that if you use double quotes, you have to escape the @ with a backslash (e.g., "\@/usr/nwalsh/mybitmap").

Figure 4-7. Window showing all the default bitmaps

If you don’t want to use a bitmap, or have a different format of file (such as a GIF), you can use the -image option. First create an image pointer and then use the -image option to display the image. ...