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#include <gtk/gtk.h>
/* The expose event handler for the event box.
*
* This function simply draws a transparency onto a widget on the area
* for which it receives expose events. This is intended to give the
* event box a "transparent" background.
*
* In order for this to work properly, the widget must have an RGBA
* colourmap. The widget should also be set as app-paintable since it
* doesn't make sense for GTK+ to draw a background if we are drawing it
* (and because GTK+ might actually replace our transparency with its
* default background colour).
*/
static gboolean
transparent_expose (GtkWidget *widget,
GdkEventExpose *event)
{
cairo_t *cr;
g_print("entry transparent_expose\n");
cr = gdk_cairo_create (widget->window);
cairo_set_operator (cr, CAIRO_OPERATOR_CLEAR);
gdk_cairo_region (cr, event->region);
cairo_fill (cr);
cairo_destroy (cr);
return FALSE;
}
/* The expose event handler for the window.
*
* This function performs the actual compositing of the event box onto
* the already-existing background of the window at 50% normal opacity.
*
* In this case we do not want app-paintable to be set on the widget
* since we want it to draw its own (red) background. Because of this,
* however, we must ensure that we use g_signal_connect_after so that
* this handler is called after the red has been drawn. If it was
* called before then GTK would just blindly paint over our work.
*
* Note: if the child window has children, then you need a cairo 1.6
* feature to make this work correctly.
*/
static gboolean
window_expose_event (GtkWidget *widget,
GdkEventExpose *event)
{
GdkRegion *region;
GtkWidget *child;
cairo_t *cr;
g_print("entry window_expose_event\n");
/* get our child (in this case, the event box) */
child = gtk_bin_get_child (GTK_BIN (widget));
/* create a cairo context to draw to the window */
cr = gdk_cairo_create (widget->window);
/* the source data is the (composited) event box */
gdk_cairo_set_source_pixmap (cr, child->window,
child->allocation.x,
child->allocation.y);
/* draw no more than our expose event intersects our child */
region = gdk_region_rectangle (&child->allocation);
gdk_region_intersect (region, event->region);
gdk_cairo_region (cr, region);
cairo_clip (cr);
/* composite, with a 50% opacity */
cairo_set_operator (cr, CAIRO_OPERATOR_OVER);
cairo_paint_with_alpha (cr, 0.5);
/* we're done */
cairo_destroy (cr);
return FALSE;
}
int
main (int argc, char **argv)
{
GtkWidget *window, *event, *button;
GdkScreen *screen;
GdkColormap *rgba;
GdkColor red;
gtk_init (&argc, &argv);
/* Make the widgets */
button = gtk_button_new_with_label ("A Button");
event = gtk_event_box_new ();
window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
/* Put a red background on the window */
gdk_color_parse ("green", &red);
gtk_widget_modify_bg (window, GTK_STATE_NORMAL, &red);
/* Set the colourmap for the event box.
* Must be done before the event box is realised.
*/
screen = gtk_widget_get_screen (event);
rgba = gdk_screen_get_rgba_colormap (screen);
gtk_widget_set_colormap (event, rgba);
/* Set our event box to have a fully-transparent background
* drawn on it. Currently there is no way to simply tell GTK+
* that "transparency" is the background colour for a widget.
*/
gtk_widget_set_app_paintable (GTK_WIDGET (event), TRUE);
g_signal_connect (event, "expose-event",
G_CALLBACK (transparent_expose), NULL);
/* Put them inside one another */
gtk_container_set_border_width (GTK_CONTAINER (window), 10);
gtk_container_add (GTK_CONTAINER (window), event);
gtk_container_add (GTK_CONTAINER (event), button);
/* Realise and show everything */
gtk_widget_show_all (window);
/* Set the event box GdkWindow to be composited.
* Obviously must be performed after event box is realised.
*/
gdk_window_set_composited (event->window, TRUE);
/* Set up the compositing handler.
* Note that we do _after_ so that the normal (red) background is drawn
* by gtk before our compositing occurs.
*/
g_signal_connect_after (window, "expose-event",
G_CALLBACK (window_expose_event), NULL);
gtk_main ();
return 0;
} |
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發(fā)表于 2011-06-22 08:00
