问题
If I create a normal GtkWindow with nothing inside or a GtkWindow with a GtkDrawingArea inside (or that inside a GtkScrolledWindow), I get a window with the theme's background, as in this picture.
But if I use a GtkLayout, I get a window with a solid color background, as in this picture.
The only resource anyone (myself included) could find so far was this other Stack Overflow question, but when I do what it says to do, I get a fully black background, like in this picture, even if I get a cairo context for the GtkLayout's bin window.
So how exactly do I get the GtkLayout to be transparent, or if that's not an option, to use the theme's background?
Though I am running with GTK+ 3.10, I need to target GTK+ 3.4, so gtk_widget_set_opacity() won't work. The theme shown in my screenshots is the gtk-oxygen theme; I am using KDE.
Sample program below. It has options to cover all the cases I described above. I also tried variations of the various cairo calls in draw() (commenting some out, adding another alpha color selection after setting CLEAR, not setting a clip rect, etc.); that didn't work either.
Thanks!
/* pietro gagliardi - 7-8 april 2014 */
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#define GDK_VERSION_MIN_REQUIRED GDK_VERSION_3_4
#define GDK_VERSION_MAX_ALLOWED GDK_VERSION_3_4
#include <gtk/gtk.h>
gboolean windowonly = FALSE;
gboolean drawingarea = FALSE;
gboolean viewport = FALSE;
gboolean drawsig = FALSE;
gboolean binwin = FALSE;
void parseargs(int argc, char *argv[])
{
if (argc != 2 && argc != 3)
goto usage;
#define extra(str) (argc == 3 && strcmp(argv[2], str) == 0)
#define noextra(cond) if (!(cond) && argc == 3) goto usage;
if (strcmp(argv[1], "windowOnly") == 0) {
noextra(FALSE);
windowonly = TRUE;
return;
} else if (strcmp(argv[1], "drawingArea") == 0) {
drawingarea = TRUE;
viewport = extra("viewport");
noextra(viewport);
return;
} else if (strcmp(argv[1], "layout") == 0) {
binwin = extra("drawbin");
drawsig = binwin || extra("draw");
noextra(drawsig);
return;
}
usage:
fprintf(stderr, "usage:\n");
fprintf(stderr, "\t%s windowOnly\n", argv[0]);
fprintf(stderr, "\t%s drawingArea [viewport]\n", argv[0]);
fprintf(stderr, "\t%s layout [draw|drawbin]\n", argv[0]);
exit(1);
}
gboolean draw(GtkWidget *widget, cairo_t *cr, gpointer data)
{
double x, y, w, h;
if (binwin)
cr = gdk_cairo_create(gtk_layout_get_bin_window((GtkLayout *) widget));
cairo_clip_extents(cr, &x, &y, &w, &h);
cairo_set_operator(cr, CAIRO_OPERATOR_CLEAR);
cairo_rectangle(cr, x, y, w, h);
cairo_fill(cr);
cairo_set_operator(cr, CAIRO_OPERATOR_OVER);
cairo_set_source_rgba(cr, 0, 0, 0, 0);
cairo_rectangle(cr, x, y, w, h);
cairo_fill(cr);
if (binwin)
cairo_destroy(cr);
return FALSE;
}
int main(int argc, char *argv[])
{
GtkWidget *w;
GtkWidget *q;
parseargs(argc, argv);
gtk_init(NULL, NULL);
w = gtk_window_new(GTK_WINDOW_TOPLEVEL);
g_signal_connect(w, "destroy", G_CALLBACK(gtk_main_quit), NULL);
if (!windowonly) {
if (drawingarea) {
q = gtk_drawing_area_new();
if (viewport) {
GtkWidget *sw;
sw = gtk_scrolled_window_new(NULL, NULL);
gtk_scrolled_window_add_with_viewport(GTK_SCROLLED_WINDOW(sw), q);
q = sw;
}
} else {
q = gtk_layout_new(NULL, NULL);
if (drawsig)
g_signal_connect(q, "draw", G_CALLBACK(draw), NULL);
}
gtk_container_add(GTK_CONTAINER(w), q);
}
gtk_widget_show_all(w);
gtk_main();
return 0;
}
回答1:
Add a GtkCssProvider to your window with one or both of
GtkLayout {
background-color: transparent;
}
GtkViewport {
background-color: transparent;
}
loaded in it. You may also be able to do this with gtk_widget_override_background_color().
回答2:
They key is to set a proper RGBA visual for the window
w = //some GtkWidget, I used the GtkWindow to test
gtk_widget_set_app_paintable (w, TRUE); // important or you will get solid color
GdkScreen *screen = gtk_widget_get_screen (w);
GdkVisual *visual = gdk_screen_get_rgba_visual (screen);
gtk_widget_set_visual(w, visual);
gtk_widget_show_all(w);
Note: Also do
g_signal_connect(G_OBJECT(w), "screen-changed", G_CALLBACK(screen_changed_contaniing_above_code), NULL);
or weird things might happen on certain multi screen setups (could not reproduce with my local), but well.. just do it, you can't know how Xinerama or other X extensions react when dragging the window between screens...
See this SO question which has a complete compileable example.
Also I'd recommend to draw only once using CAIRO_OPERATOR_SOURCE.
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#define GDK_VERSION_MIN_REQUIRED GDK_VERSION_3_4
#define GDK_VERSION_MAX_ALLOWED GDK_VERSION_3_4
#include <gtk/gtk.h>
gboolean draw(GtkWidget *widget, cairo_t *cr, gpointer data)
{
double x, y, w, h;
cairo_clip_extents(cr, &x, &y, &w, &h);
cairo_set_source_rgba (cr, 1., 0., 0., 0.25); //translucent red
cairo_set_operator(cr, CAIRO_OPERATOR_SOURCE);
cairo_rectangle(cr, x, y, w, h);
cairo_fill(cr);
return FALSE;
}
void fix_visual(GtkWidget *w)
{
GdkScreen *screen = gtk_widget_get_screen (w);
GdkVisual *visual = gdk_screen_get_rgba_visual (screen);
gtk_widget_set_visual(w, visual);
//FIXME cleanup maybe
}
void screen_changed (GtkWidget *widget, GdkScreen *screen, gpointer user_data)
{
fix_visual (widget);
}
int main(int argc, char *argv[])
{
GtkWidget *w;
GtkWidget *q;
gtk_init(&argc, &argv);
w = gtk_window_new(GTK_WINDOW_TOPLEVEL);
g_signal_connect(w, "destroy", G_CALLBACK(gtk_main_quit), NULL);
q = gtk_layout_new(NULL, NULL);
g_signal_connect(w, "screen-changed", G_CALLBACK(screen_changed), NULL);
g_signal_connect(q, "draw", G_CALLBACK(draw), NULL);
gtk_container_add(GTK_CONTAINER(w), q);
gtk_widget_set_app_paintable (w, TRUE);
fix_visual (w);
gtk_widget_show_all(w);
gtk_main();
return 0;
}
来源：https://stackoverflow.com/questions/22940588/how-do-i-really-make-a-gtk-3-gtklayout-transparent-draw-theme-background