Le mercredi 23 juillet 2008 à 10:38 +0200, Yann Droneaud a écrit :
> Hi,
>
> I'm trying to write a program to display a picture with full
> transparency in its own window (without border), using Composite
> extension (ARGB colormap and visual).
>
Using Cairo correctly (e.g. using operator CAIRO_OPERATOR_SOURCE) fixes
my problems, see below.
> So here are my little demonstration programs
>
> - test-gdkpixbuf.c :
>
> This program does the following:
> - looks up the RGBA colormap with gdk_screen_get_rgba_colormap()
> - installs the colormap with gtk_widget_set_default_colormap()
> - creates a GdkPixbuf with gdk_pixbuf_new_from_file()
> - creates a GtkWindow
> - sets the widget as GTK_APP_PAINTABLE with
> gtk_widget_set_app_paintable()
> - disables double buffering with gtk_widget_set_double_buffered()
> - in the realize signal handler, it removes any background pixmap
> using gdk_window_set_back_pixmap()
> - in the expose event handler, it draws the GdkPixBuf using
> gdk_draw_pixbuf()
>
Problem:
- gdk_draw_pixbuf() seems to use Cairo with operator CAIRO_OPERATOR_OVER
so it composes the GdkPixbuf with the background of the window (or
the content of the root window, if it has no background).
Two way to fix:
Fill the window with a black, full transparency content before
calling gdk_draw_pixbuf(): in expose_event():
...
cairo_t *cr = gdk_cairo_create(widget->window);
cairo_set_operator(cr, CAIRO_OPERATOR_SOURCE);
cairo_set_source_rgba(cr, 0.0, 0.0, 0.0, 0.0);
cairo_paint(cr);
cairo_destroy(cr);
gdk_draw_pixbuf(widget->window,
...
Or, better, use gdk_cairo_set_source_pixbuf() instead of
gdk_draw_pixbuf():
...
cairo_t *cr = gdk_cairo_create(widget->window);
gdk_cairo_region(cr, event->region);
cairo_set_operator(cr, CAIRO_OPERATOR_SOURCE);
gdk_cairo_set_source_pixbuf(cr, pixbuf, 0.0, 0.0);
cairo_paint(cr);
cairo_destroy(cr);
...
Here, I was using CAIRO_OPERATOR_OVER in my first tests, so the
results were the same than with gdk_draw_pixbuf(). My mistake.
Fixed program is test-gdkpixbuf-cairo.c
> - test-gdkpixbuf-bg.patch:
>
> Apply the patch on top of test-gdkpixbuf.c to create
> test-gdkpixbuf-background.c
> This patch set a pixmap as a background, and draw nothing on the
> window. Only the realize signal and expose event handlers are
> modified:
> - realize signal handler creates a new pixmap with gdk_pixmap_new(),
> writes the content of the GdkPixBuf with gdk_draw_pixbuf() and then
> install the background with gdk_window_set_back_pixmap().
> - expose event handler only call to gdk_window_clear()
>
Problems:
- gdk_create_pixmap() returns a GdkPixmap with undefined content
- gdk_draw_pixbuf() composes the GdkPixbuf's content with the
undefined content of the GdkPixmap
See my post[1] titled "There's something in my pixmap".
Same fixes two can be applied here: either initialize the content of the
drawable before calling gdk_draw_pixbuf(), either use only cairo to
draw the GdkPixbuf with the correct operator: CAIRO_OPERATOR_SOURCE.
Remark: I'm still interested in a version using only GDK drawing
functions and no Cairo functions.
Regards.
[1] http://mail.gnome.org/archives/gtk-list/2008-July/msg00107.html
--
Yann Droneaud <ydroneaud@xxxxxxxxxxxx>
/* test-gdkpixbuf-cairo.c - draw a RGBA image in a window using Cairo
*
* Yann Droneaud <ydroneaud@xxxxxxxxxxxx>
*
*/
#include <gtk/gtk.h>
#include <gdk/gdk.h>
#include <gdk/gdkkeysyms.h>
#include <gdk-pixbuf/gdk-pixbuf.h>
static void
realize_signal(GtkWidget *widget,
gpointer data)
{
gdk_window_set_back_pixmap(widget->window, NULL, FALSE);
return;
}
static void
destroy_signal(GtkWidget *widget,
gpointer data)
{
gtk_main_quit();
return;
}
static gboolean
button_press_event(GtkWidget *widget,
GdkEventButton *event,
gpointer data)
{
if (event->button == 1 && (event->state & GDK_CONTROL_MASK)) {
gtk_window_begin_move_drag(GTK_WINDOW(widget),
(gint) event->button,
(gint) event->x_root,
(gint) event->y_root,
event->time);
return TRUE;
}
return FALSE;
}
static gboolean
key_press_event(GtkWidget *widget,
GdkEventKey *event,
gpointer data)
{
/* handle move if mouse button is pressed and later ctrl is hit */
if ((event->keyval == GDK_Control_L ||
event->keyval == GDK_Control_R) &&
(event->state & GDK_BUTTON1_MASK)) {
gint x;
gint y;
gdk_display_get_pointer(gdk_display_get_default(),
NULL, /* screen */
&x,
&y,
NULL); /* state */
gtk_window_begin_move_drag(GTK_WINDOW(widget),
(gint) 1, /* first button, see mask */
x,
y,
event->time);
return TRUE;
}
if (event->keyval == GDK_Escape) {
gtk_main_quit();
return TRUE;
}
return FALSE; /* event not handled */
}
static gboolean
expose_event(GtkWidget *widget,
GdkEventExpose *event,
gpointer data)
{
GdkPixbuf *pixbuf = (GdkPixbuf *) data;
cr = gdk_cairo_create(widget->window);
gdk_cairo_region(cr, event->region);
cairo_set_operator(cr, CAIRO_OPERATOR_SOURCE);
gdk_cairo_set_source_pixbuf(cr, pixbuf, 0.0, 0.0);
cairo_paint(cr);
cairo_destroy(cr);
return TRUE;
}
int
main(int argc,
char *argv[])
{
GdkScreen *screen;
GtkWidget *window;
GdkColormap *colormap;
const char *color_name = NULL;
GdkColor color;
const char *pixbuf_name = NULL;
GdkPixbuf *pixbuf;
GError *error = NULL;
gtk_init (&argc, &argv);
if (argc > 1 && argv[1] != NULL && *argv[1] != '\0') {
pixbuf_name = argv[1];
}
if (argc > 2 && argv[2] != NULL && *argv[2] != '\0') {
color_name = argv[2];
}
if (pixbuf_name == NULL) {
g_printerr("missing parameter\n");
return 1;
}
/* get RGBA colormap */
screen = gdk_screen_get_default();
colormap = gdk_screen_get_rgba_colormap(screen);
if (colormap == NULL) {
g_printerr("no RGBA colormap\n");
return 1;
}
/* use the RGBA colormap */
gtk_widget_set_default_colormap(colormap);
/* load the pixbuf */
pixbuf = gdk_pixbuf_new_from_file(argv[1], &error);
if (pixbuf == NULL) {
g_printerr("can't load pixbuf\n");
return 1;
}
/* check pixbuf format */
if (gdk_pixbuf_get_has_alpha(pixbuf) != TRUE ||
gdk_pixbuf_get_n_channels(pixbuf) != 4 ||
gdk_pixbuf_get_bits_per_sample(pixbuf) != 8) {
g_printerr("incorrect pixbuf format !\n");
return 1;
}
window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
gtk_widget_set_app_paintable(window, TRUE);
gtk_widget_set_double_buffered(window, FALSE);
/* unneeded, see gtk_widget_set_default_colormap() */
gtk_widget_set_colormap(window, colormap);
gtk_window_set_decorated(GTK_WINDOW(window), FALSE);
gtk_window_set_resizable(GTK_WINDOW(window), FALSE);
gtk_window_set_title(GTK_WINDOW(window), "simple");
gtk_widget_set_size_request(window,
gdk_pixbuf_get_width(pixbuf),
gdk_pixbuf_get_height(pixbuf));
if (color_name != NULL) {
gdk_color_parse(color_name, &color);
gtk_widget_modify_bg(window, GTK_STATE_NORMAL, &color);
}
g_signal_connect_after(G_OBJECT(window), "realize",
G_CALLBACK(realize_signal), NULL);
g_signal_connect(G_OBJECT(window), "destroy",
G_CALLBACK(destroy_signal), NULL);
g_signal_connect(G_OBJECT(window), "key_press_event",
G_CALLBACK(key_press_event), NULL);
g_signal_connect(G_OBJECT(window), "button_press_event",
G_CALLBACK(button_press_event), NULL);
g_signal_connect(G_OBJECT(window), "expose_event",
G_CALLBACK(expose_event), pixbuf);
gtk_widget_add_events(window,
GDK_EXPOSURE_MASK
| GDK_BUTTON_PRESS_MASK
| GDK_KEY_PRESS_MASK);
gtk_widget_show(window);
gtk_main ();
return 0;
}
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