Re: Drawing text into a drawing area with Pango

[Peter Krueger <pkrueger appss de>]

On Tue, 17 Feb 2004, Bryan Brown wrote:
> Problem is, it's not clear to me what parts of the Pango context and
> layout I need to initialize other than the text string.  Here's a snippet
> of the code that I've tried so far:
>
> === begin code snippet ===
>
> PangoContext *context;
> PangoLayout  *layout;
> gchar *text_buffer[] = "BLAH";
> GdkEventButton *event;
> GdkGC *gc;
> gint x_start, y_start;
>
> [snip]
>
>    context = (PangoContext *) pango_context_new ();
>    layout  = pango_layout_new (context);
>    pango_layout_set_text (layout, text_buffer, -1);
>
> [snip]
>
>    x_start = event->x;
>    y_start = event->y;
>
>    gdk_draw_layout (drawing_area->window,
>                     gc,
>                     x_start,
>                     y_start,
>                     layout);
>
> === end code snippet ===
>
> This causes an abend in the call to gdk_draw_layout when run, presumably
> because I've not initialized some items in the Pango context and/or
> layout.
>
> What other items do I need to initialize?  I can't readily find some
> "simple", sample code to illustrate the process, hence my appeal for help.

Hello Bryan,
at first you don't need to create a PangoContext yourself. You can create
the layout directly from your drawingarea widget:
PangoLayout *pLayout = gtk_widget_create_pango_layout(drawing_area, 0);

Then set the text and draw it like you did. After you printed your text
free the PangoLayout with g_object_unref(pLayout).
From your code snipped I guess you forgot to initialize the gc. You can
create your own graphics context with:
gc = gdk_gc_new(drawing_area->window);
and free it when you don't need it anymore with:
g_object_unref(gc);
Create the gc just before you need it to make sure that the widget is
already realized and drawing_area->window is valid.

The drawing area also contains a couple of graphics contexts inside its
GtkStyle. If you would like to use one of them instead of creating your
own try something like
gc = gtk_widget_get_style(drawing_area)->fg_gc[GTK_STATE_NORMAL]
and see if it fits your needs. In this case you don't have to free the
graphics context. But remember that you must not change any attributes
inside such a "borrowed" gc. GTK eventually shares graphics contexts
between different widgets and changing attributes of such a gc has weird
effects on your user interface.

Regards,
                   Peter
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Peter Krüger

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