forked from AuroraMiddleware/gtk
137 lines
4.2 KiB
Plaintext
137 lines
4.2 KiB
Plaintext
<!-- ##### SECTION Title ##### -->
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GtkDrawingArea
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<!-- ##### SECTION Short_Description ##### -->
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A widget for custom user interface elements
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<!-- ##### SECTION Long_Description ##### -->
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<para>
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The #GtkDrawingArea widget is used for creating custom user interface
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elements. It's essentially a blank widget; you can draw on
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<literal>widget->window</literal>. After creating a drawing area,
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the application may want to connect to:
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<itemizedlist>
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<listitem>
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<para>
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Mouse and button press signals to respond to input from
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the user. (Use gtk_widget_add_events() to enable events
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you wish to receive.)
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</para>
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</listitem>
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<listitem>
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<para>
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The "realize" signal to take any necessary actions
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when the widget is instantiated on a particular display.
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(Create GDK resources in response to this signal.)
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</para>
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</listitem>
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<listitem>
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<para>
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The "configure_event" signal to take any necessary actions
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when the widget changes size.
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</para>
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</listitem>
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<listitem>
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<para>
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The "expose_event" signal to handle redrawing the
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contents of the widget.
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</para>
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</listitem>
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</itemizedlist>
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</para>
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<para>
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The following code portion demonstrates using a drawing
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area to display a circle in the normal widget foreground
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color.
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Note that GDK automatically clears the exposed area
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to the background color before sending the expose event, and
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that drawing is implicitly clipped to the exposed area.
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</para>
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<example>
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<title>Simple <structname>GtkDrawingArea</structname> usage.</title>
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<programlisting>
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gboolean
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expose_event_callback (GtkWidget *widget, GdkEventExpose *event, gpointer data)
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{
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gdk_draw_arc (widget->window,
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widget->style->fg_gc[GTK_WIDGET_STATE (widget)],
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TRUE,
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0, 0, widget->allocation.width, widget->allocation.height,
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0, 64 * 360);
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return TRUE;
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}
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[...]
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GtkWidget *drawing_area = gtk_drawing_area_new (<!-- -->);
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gtk_widget_set_size_request (drawing_area, 100, 100);
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g_signal_connect (G_OBJECT (drawing_area), "expose_event",
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G_CALLBACK (expose_event_callback), NULL);
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</programlisting>
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</example>
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<para>
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Expose events are normally delivered when a drawing area first comes
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onscreen, or when it's covered by another window and then uncovered
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(exposed). You can also force an expose event by adding to the "damage
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region" of the drawing area's window; gtk_widget_queue_draw_area() and
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gdk_window_invalidate_rect() are equally good ways to do this. You'll
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then get an expose event for the invalid region.
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</para>
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<para>
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The available routines for drawing are documented on the <link
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linkend="gdk-Drawing-Primitives">GDK Drawing Primitives</link> page.
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See also gdk_pixbuf_render_to_drawable() for drawing a #GdkPixbuf.
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</para>
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<para>
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To receive mouse events on a drawing area, you will need to enable
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them with gtk_widget_add_events(). To receive keyboard events, you
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will need to set the #GTK_CAN_FOCUS flag on the drawing area, and
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should probably draw some user-visible indication that the drawing
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area is focused. Use the GTK_HAS_FOCUS() macro in your expose event
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handler to decide whether to draw the focus indicator. See
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gtk_paint_focus() for one way to draw focus.
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</para>
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<!-- ##### SECTION See_Also ##### -->
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<para>
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Sometimes #GtkImage is a useful alternative to a drawing area.
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You can put a #GdkPixmap in the #GtkImage and draw to the #GdkPixmap,
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calling gtk_widget_queue_draw() on the #GtkImage when you want to
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refresh to the screen.
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</para>
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<!-- ##### STRUCT GtkDrawingArea ##### -->
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<para>
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The #GtkDrawingArea struct contains private data only, and
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should be accessed using the functions below.
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</para>
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<!-- ##### FUNCTION gtk_drawing_area_new ##### -->
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<para>
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Creates a new drawing area.
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</para>
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@Returns: a new #GtkDrawingArea
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<!-- ##### FUNCTION gtk_drawing_area_size ##### -->
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<para>
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(Use gtk_widget_set_size_request() instead.)
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Sets the size that the drawing area will request
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in response to a "size_request" signal. The
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drawing area may actually be allocated a size
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larger than this depending on how it is packed
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within the enclosing containers.
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</para>
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@darea: a #GtkDrawingArea.
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@width: the width to request.
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@height: the height to request.
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