From 2b0887c9ab23acd04c932d154ee1e687a45c7363 Mon Sep 17 00:00:00 2001
From: Nick Gasson <nick@nickg.me.uk>
Date: Thu, 1 Oct 2020 12:16:55 +0800
Subject: [PATCH] Fix black background on non-composited displays

---
 src/floating_shape.c | 23 +++++++++++++++++++----
 src/floating_shape.h |  2 +-
 2 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/src/floating_shape.c b/src/floating_shape.c
index f49d42a..dfbd1c5 100644
--- a/src/floating_shape.c
+++ b/src/floating_shape.c
@@ -41,6 +41,8 @@ static gboolean draw_shape(GtkWidget *widget, GdkEventExpose *event,
    float_shape_t *s = (float_shape_t *)userdata;
    cairo_t *cr;
    int width, height;
+   GdkWindow *root_win;
+   GdkPixbuf *root_pb;
 
    cr = gdk_cairo_create(gtk_widget_get_window(widget));
 
@@ -48,6 +50,20 @@ static gboolean draw_shape(GtkWidget *widget, GdkEventExpose *event,
 
    gtk_window_get_size(GTK_WINDOW(widget), &width, &height);
 
+   if (!s->composited) {
+      // Gtk3 removed the gtk_widget_shape_combine_mask() function so to
+      // support transparency on a non-composited display we first
+      // capture the root window and use that as a backgroud for the
+      // floating shape.
+      root_win = gdk_get_default_root_window();
+      root_pb = gdk_pixbuf_get_from_window(root_win, s->x, s->y, width, height);
+
+      gdk_cairo_set_source_pixbuf(cr, root_pb, 0, 0);
+      cairo_paint(cr);
+
+      g_object_unref(root_pb);
+   }
+
    gdk_cairo_set_source_pixbuf(cr, s->pixbuf, 0, 0);
    cairo_paint(cr);
 
@@ -93,10 +109,9 @@ float_shape_t *make_shape_from_pixbuf(GdkPixbuf *pixbuf)
    screen = gtk_widget_get_screen(s->window);
    visual = gdk_screen_get_rgba_visual(screen);
 
-   gtk_widget_set_visual(s->window, visual);
-
-   if (!gdk_screen_is_composited(screen)) {
-      fprintf(stderr, "Warning: display does not support alpha channel\n");
+   if (gdk_screen_is_composited(screen) && visual) {
+      gtk_widget_set_visual(s->window, visual);
+      s->composited = true;
    }
 
    g_signal_connect(G_OBJECT(s->window), "draw",
diff --git a/src/floating_shape.h b/src/floating_shape.h
index 535aad0..599c314 100644
--- a/src/floating_shape.h
+++ b/src/floating_shape.h
@@ -28,7 +28,7 @@ typedef struct {
    GtkWidget *window;
    GdkPixbuf *pixbuf;
    int x, y, width, height;
-   bool has_rgba;
+   bool composited;
 } float_shape_t;
 
 float_shape_t *make_shape_from_pixbuf(GdkPixbuf *pixbuf);
-- 
2.39.2