Question

The following two lines of code load an image from an SVG file and set it as the icon for a window:

GdkPixbuf *icon = gdk_pixbuf_new_from_file("icon.svg", NULL);
gtk_window_set_icon(GTK_WINDOW(win), icon);

This SVG file contains, among other things, a rectangle defined like:

<rect
   style="fill:#000000"
   id="screen"
   ... />

I would like to dynamically change the color of this rect element after I’ve loaded the file, but before I set it as the icon for the window.

If I manually change the style attribute on this element of the file on disk just before I start my program, it has the desired effect. But I would like to have it set by the program itself, to match a colour it has chosen.

(This is so I can distinguish multiple similar windows in the window switcher menu, among other places)

Answer 1

I’ve now found the answer to this, from IRC (#gtk+ on irc.gnome.org), and reading GTK’s own source code.

The answer involves building a string that sets a stylesheet and uses XML’s xinclude to pull in the original image.

GdkPixbuf *load_icon(char *background)
{
  /* This technique stolen from 
   *   http://git.gnome.org/browse/gtk+/tree/gtk/gtkicontheme.c#n3180
   */

  gchar *str = g_strconcat(
      "<?xml version=\"1.0\" encoding=\"UTF-8\" standalone=\"no\"?>\n"
      "<svg version=\"1.1\"\n"
      "     xmlns=\"http://www.w3.org/2000/svg\"\n"
      "     xmlns:xi=\"http://www.w3.org/2001/XInclude\"\n"
      "     width=\"64\"\n"
      "     height=\"64\">\n"
      "  <style type=\"text/css\">\n"
      "    #screen {\n"
      "      fill: ", background, " !important;\n"
      "    }\n"
      "  </style>\n"
      "  <xi:include href=\"" PANGOTERM_SHAREDIR "/pangoterm.svg" "\"/>\n"
      "</svg>",
    NULL);

  GInputStream *stream = g_memory_input_stream_new_from_data(str, -1, g_free);

  GdkPixbuf *ret = gdk_pixbuf_new_from_stream(stream, NULL, NULL);

  g_object_unref(stream);

  return ret;
}