Re: gtk_widget_modify_fg() problems

[Soeren Sandmann <sandmann daimi au dk>]

"Rikke D. Giles" <rgiles telebyte com> writes:

> I'm developing a complicated dial widget to use in a weather analysis
> program.  The widget goes beyond the dial widget in the gtk tutorial,
> in that you can set the upper and lower boundaries, set 'danger' and
> 'critical' levels.  It uses a pangolayout to show a title, units (such
> as m/s or joules/hour or whatever) and the current dial reading.  It's
> not sensitive, it's meant for data output as opposed to input.  It
> also uses a pixmap for rendering, eliminating screen flicker and so
> on.

That is not necessary, because as long as you only draw in an expose
handler, gtk+ will automatically redirect the drawing to a
pixmap. Then when the expose handler finishes, gtk+ will draw the
pixmap to the screen. In other words, gtk+ automatically double
buffers the drawing as long as it happens in an expose handler.

> I'm trying to change the color in the dial_expose() function by using:
>
> Gdkcolor color;
>
> gdk_parse_color("red", color);
> gtk_widget_modify_fg(widget, &color);
>
> this is straight from the mini-FAQ on color in GTK.

You are probably not understanding gtk_widget_modify_fg(). You can't
call that function out of an expose handler.

Conceptually gtk_widget_modify_fg(widget, NULL) means "set the
foreground color of the widget, permanently", which is something else
than "temporarily change the color of the fg_gc". When you call
gtk_widget_modify_fg() it means a property of the widget has changed,
so the widget needs to be redrawn. This means the expose event will be
emitted again, causing the loop.

> gdk_parse_color("red", color);
> gtk_widget_modify_fg(widget, &color);
> gdk_draw_line (widget->window,
>                       widget->style->fg_gc[widget->state],
>                       xc + c*(dial->radius - tick_length),
>                       yc - s*(dial->radius - tick_length),
>                       xc + c*dial->radius,
>                       yc - s*dial->radius);
> ....
> ...
> ...
> gtk_widget_modify_fg(widget, NULL);  /* turn back to normal color */

The way to do what you want is to create a GdkGC and make it draw in
red:

    GdkGC *red_gc;
    GdkColor color = { 0, 65535, 0, 0 };
    red_gc = gdk_gc_new (widget->window);
    gdk_gc_set_rgb_fg_color (red_gc, &color);

    gdk_draw_line (widget->window, red_gc, ...);

    g_object_unref (G_OBJECT (red_gc));


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