In wxGlade some widgets need to specify a bitmap path. You can use any graphic format supported by wxWidgets.
The bitmap can be specified in several ways:
Usually you can type an absolute path in a text box or browse for
      a bitmap with a file dialog. This will produce a
      wxBitmap object with the typed string as bitmap
      path (e.g. wxBitmap("/usr/share/icons/application.png",
      wxBITMAP_TYPE_ANY))
You can enter a variable name using the var:
      tag in the text box. This will produce a wxBitmap
      object with the variable name as bitmap path (e.g.
      var:my_bitmap_path produces
      wxBitmap(my_bitmap_path, wxBITMAP_TYPE_ANY)). In
      Perl code generation a “$” sign is added if you omit
      it.
You can enter a code chunk returning a
      wxBitmap, by using the code:
      tag. This inserts verbatim the code you enter in brackets and nothing
      more (e.g.: if wxSomeWidget needs a
      wxBitmap as an argument, the string
      code:if (x == 0) get_bitmap1() else get_bitmap2();
      produces wxSomeWidget((if (x == 0) get_bitmap1() else
      get_bitmap2();), option1, option2)).
wxGlade never declares or assigns variable or function names, so after code generation, you have to provide extra code to declare your variables or functions.
If you use var: or code: tags the preview window shows an empty bitmap of fixed size.