GTK+2: gdk_draw_arc() -- changing arc colour

[Chris Martin <c martin sheffield ac uk>]

In the example shown in GTK API/Miscellaneous/GtkDrawingArea it seems
impossible to change the colour the arc is drawn in.

Has anybody a solution to this?

Two examples of code tried -- the first is the "simple" method, the
second a more devious one: seeing that gdk_gc_new() called
gdk_gc_new_with_values() it seemed possible that supplying it with
values might work...

Example 1:

gboolean
expose_event_callback(GtkWidget * widget, GdkEventExpose * event,
                      gpointer data)
{
  GdkGC *gc;
  GdkColor colour;

  memset(&colour, 0, sizeof(colour));
  if (gdk_color_parse(colour_str, &colour)) {
    g_print("gdk_color_parse(%s) succeeds.\n", colour_str);
    g_print("colour: pixel %lu, red 0x%04x, green 0x%04x, blue 0x%04x.\n",
            colour.pixel, colour.red, colour.green, colour.blue);
    g_print("colour: pixel %lu, red %u, green %u, blue %u.\n",
            colour.pixel, colour.red>>8, colour.green>>8, colour.blue>>8);
  } else
    g_print("gdk_color_parse(%s) fails.\n", colour_str);

  gc = gdk_gc_new(widget->window);
  gdk_gc_set_foreground(gc, &colour);

  gdk_draw_arc(widget->window, gc, TRUE,
               0, 0, widget->allocation.width, widget->allocation.height,
               0, 64 * 360);
  return TRUE;
}

Example 2:

gboolean
expose_event_callback(GtkWidget * widget, GdkEventExpose * event,
                      gpointer data)
{
  GdkGC *gc;
  GdkGCValues values;
  GdkColor colour;

  gdk_gc_get_values(widget->style->fg_gc[GTK_WIDGET_STATE(widget)], &values);

  memset(&colour, 0, sizeof(colour));
  if (gdk_color_parse(colour_str, &colour)) {
    g_print("gdk_color_parse(%s) succeeds.\n", colour_str);
    g_print("colour: pixel %lu, red 0x%04x, green 0x%04x, blue 0x%04x.\n",
            colour.pixel, colour.red, colour.green, colour.blue);
    g_print("colour: pixel %lu, red %u, green %u, blue %u.\n",
            colour.pixel, colour.red>>8, colour.green>>8, colour.blue>>8);
  } else
    fprintf(stderr, "gdk_color_parse(%s) fails.\n", colour_str);

  values.foreground = colour;

  gc = gdk_gc_new_with_values(widget->window, &values, GDK_GC_FOREGROUND);

  gdk_draw_arc(widget->window, gc, TRUE,
               0, 0, widget->allocation.width, widget->allocation.height,
               0, 64 * 360);

  return TRUE;
}

In both cases the filled arc is drawn in black -- the output shows
that the colour was parsed correctly and the GdkColor was set
correctly:

Example 1:

$ ./try-colour1
gdk_color_parse(LightGrey) succeeds.
colour: pixel 0, red 0xd3d3, green 0xd3d3, blue 0xd3d3.
colour: pixel 0, red 211, green 211, blue 211.

Example 2:
$ ./try-colour2
gdk_color_parse(LightGrey) succeeds.
colour: pixel 0, red 0xd3d3, green 0xd3d3, blue 0xd3d3.
colour: pixel 0, red 211, green 211, blue 211.