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 Post subject: Transparent image application over GTK-DirectFB
PostPosted: Fri Dec 22, 2006 12:03 pm 
Familiar Face

Joined: Fri Dec 08, 2006 6:44 am
Posts: 11

I have drawn a rectangle over a Pixmap and over the rectangle drawn a Pixbuf (transparent image).

whenver the pixbuf(transparent image) is totallly inside the rectangle the transparency effect is there. but when I tried to draw the pixbuf outside
rectangle the background color of pixbuf (transparent image) becomes black..

Why any transparent image which is drawn over a pixmap has background color set to black..
and the background color of pixbuf depends on the Depth of the Pixmap... For different depths of pixmap the background color of Pixbuf changes..

Depth Background color of Transparent Image.
32 Working fine in this case (shows the pixmap foreground color behind it)

Also can anyone tell how to change the foreground color of the Pixmap...

I have modified the gtk/examples/scribble-simple/scribble-simple.c for my application.. (it should be run over DirecfFB)
I'm giving the application itself.. so it will be more clear..(you must have a transparent image in the same folder to run this application)
Image should be transparent, otherwise there is no sense for the background color of the image.

#include <stdlib.h>
#include <gtk/gtk.h>

#define RECTANGLE 1
#define IMAGE 1

/* Backing pixmap for drawing area */
static GdkPixmap *pixmap = NULL;

GdkPixbuf *gdk_pixbuf = NULL;

/* Create a new backing pixmap of the appropriate size */
static gboolean configure_event( GtkWidget *widget,
GdkEventConfigure *event )
GdkColor color; = 0xffff;

if (pixmap)
g_object_unref (pixmap);

pixmap = gdk_pixmap_new (widget->window,
32); //change the depth to -1, 1, 8, 16 to see the effect in background color of the image

gdk_gc_set_rgb_fg_color (widget->style->white_gc, &color);


gdk_draw_rectangle (pixmap,


gdk_pixbuf = gdk_pixbuf_new_from_file ("2.gif", NULL); //2.gif is a transparent image
gdk_draw_pixbuf (pixmap, widget->style->black_gc, gdk_pixbuf, 0, 0, 20, 60, 150, 70, GDK_RGB_DITHER_NONE, 0, 0);

return TRUE;

/* Redraw the screen from the backing pixmap */
static gboolean expose_event( GtkWidget *widget,
GdkEventExpose *event )
GdkColor color; =0xffff; =0xffff;
//gdk_gc_set_rgb_fg_color (widget->style->fg_gc[GTK_WIDGET_STATE(widget)], &color);
gdk_draw_drawable (widget->window,
widget->style->bg_gc[GTK_WIDGET_STATE (widget)],
event->area.x, event->area.y,
event->area.x, event->area.y,
event->area.width, event->area.height);

return FALSE;

/* Draw a rectangle on the screen */
static void draw_brush( GtkWidget *widget,
gdouble x,
gdouble y)
GdkRectangle update_rect;

update_rect.x = x - 5;
update_rect.y = y - 5;
update_rect.width = 10;
update_rect.height = 10;

gdk_draw_rectangle (pixmap,
update_rect.x, update_rect.y,
update_rect.width, update_rect.height);
gtk_widget_queue_draw_area (widget,
update_rect.x, update_rect.y,
update_rect.width, update_rect.height);

static gboolean button_press_event( GtkWidget *widget,
GdkEventButton *event )
if (event->button == 1 && pixmap != NULL)
draw_brush (widget, event->x, event->y);

return TRUE;

static gboolean motion_notify_event( GtkWidget *widget,
GdkEventMotion *event )
int x, y;
GdkModifierType state;

if (event->is_hint)
gdk_window_get_pointer (event->window, &x, &y, &state);
x = event->x;
y = event->y;
state = event->state;

if (state & GDK_BUTTON1_MASK && pixmap != NULL)
draw_brush (widget, x, y);

return TRUE;

void quit ()
exit (0);

int main( int argc,
char *argv[] )
GtkWidget *window;
GtkWidget *drawing_area;
GtkWidget *vbox;

GtkWidget *button;

gtk_init (&argc, &argv);
window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
gtk_widget_set_name (window, "Test Input");

vbox = gtk_vbox_new (FALSE, 0);
gtk_container_add (GTK_CONTAINER (window), vbox);
gtk_widget_show (vbox);

g_signal_connect (G_OBJECT (window), "destroy",

/* Create the drawing area */

drawing_area = gtk_drawing_area_new ();
gtk_widget_set_size_request (GTK_WIDGET (drawing_area), 200, 200);
gtk_box_pack_start (GTK_BOX (vbox), drawing_area, TRUE, TRUE, 0);

gtk_widget_show (drawing_area);

/* Signals used to handle backing pixmap */

g_signal_connect (G_OBJECT (drawing_area), "expose_event",
G_CALLBACK (expose_event), NULL);
g_signal_connect (G_OBJECT (drawing_area),"configure_event",
G_CALLBACK (configure_event), NULL);

/* Event signals */

g_signal_connect (G_OBJECT (drawing_area), "motion_notify_event",
G_CALLBACK (motion_notify_event), NULL);
g_signal_connect (G_OBJECT (drawing_area), "button_press_event",
G_CALLBACK (button_press_event), NULL);

gtk_widget_set_events (drawing_area, GDK_EXPOSURE_MASK

/* .. And a quit button */
button = gtk_button_new_with_label ("Quit");
gtk_box_pack_start (GTK_BOX (vbox), button, FALSE, FALSE, 0);

g_signal_connect_swapped (G_OBJECT (button), "clicked",
G_CALLBACK (gtk_widget_destroy),
G_OBJECT (window));
gtk_widget_show (button);

gtk_widget_show (window);

gtk_main ();

return 0;

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