From 866cdb442c6100e340efe7a47b75b53c70338f0b Mon Sep 17 00:00:00 2001
From: Eric Koegel <eric.koegel@gmail.com>
Date: Sat, 23 Feb 2013 12:07:39 +0300
Subject: [PATCH] Clip overlapping backdrops (Bug #9052)

In a multi-monitor setup each successive wallpaper drawn has the
previous area subtracted from it so that the wallpapers aren't
drawn over each other.
---
 src/xfce-desktop.c   |   39 ++++++++++++++++++++++++++++++++++++++-
 src/xfce-workspace.c |    1 -
 2 files changed, 38 insertions(+), 2 deletions(-)

diff --git a/src/xfce-desktop.c b/src/xfce-desktop.c
index 95c30f6..fb63d00 100644
--- a/src/xfce-desktop.c
+++ b/src/xfce-desktop.c
@@ -310,6 +310,7 @@ backdrop_changed_cb(XfceBackdrop *backdrop, gpointer user_data)
     cairo_t *cr;
     GdkPixbuf *pix;
     GdkRectangle rect;
+    GdkRegion *clip_region = NULL;
     gint i, monitor = -1, current_workspace;
     
     TRACE("entering");
@@ -366,10 +367,46 @@ backdrop_changed_cb(XfceBackdrop *backdrop, gpointer user_data)
 
     cr = gdk_cairo_create(GDK_DRAWABLE(pmap));
     gdk_cairo_set_source_pixbuf(cr, pix, rect.x, rect.y);
+
+    if(monitor > 0
+       && !xfce_workspace_get_xinerama_stretch(desktop->priv->workspaces[current_workspace])) {
+        clip_region = gdk_region_rectangle(&rect);
+
+        DBG("clip_region: x: %d, y: %d, w: %d, h: %d",
+            rect.x, rect.y, rect.width, rect.height);
+
+        /* If we are not monitor 0 on a multi-monitor setup we need to subtract
+         * all the previous monitor regions so we don't draw over them. This
+         * should prevent the overlap and double backdrop drawing bugs.
+         */
+        for(i = 0; i < monitor; i++) {
+            GdkRectangle previous_monitor;
+            GdkRegion *previous_region;
+            gdk_screen_get_monitor_geometry(gscreen, i, &previous_monitor);
+
+            DBG("previous_monitor: x: %d, y: %d, w: %d, h: %d",
+                previous_monitor.x, previous_monitor.y,
+                previous_monitor.width, previous_monitor.height);
+
+            previous_region = gdk_region_rectangle(&previous_monitor);
+
+            gdk_region_subtract(clip_region, previous_region);
+
+            gdk_region_destroy(previous_region);
+        }
+
+        gdk_cairo_region(cr, clip_region);
+        cairo_clip(cr);
+    }
+
     cairo_paint(cr);
     g_object_unref(G_OBJECT(pix));
+
+    if(clip_region != NULL)
+        gdk_region_destroy(clip_region);
+
     cairo_destroy(cr);
-    
+
     /* tell gtk to redraw the repainted area */
     gtk_widget_queue_draw_area(GTK_WIDGET(desktop), rect.x, rect.y,
                                rect.width, rect.height);
diff --git a/src/xfce-workspace.c b/src/xfce-workspace.c
index ba9f327..dd32aaf 100644
--- a/src/xfce-workspace.c
+++ b/src/xfce-workspace.c
@@ -148,7 +148,6 @@ backdrop_cycle_cb(XfceBackdrop *backdrop, gpointer user_data)
     if(g_strcmp0(backdrop_file, new_backdrop) != 0) {
         xfce_backdrop_set_image_filename(backdrop, new_backdrop);
         g_free(new_backdrop);
-        g_signal_emit(G_OBJECT(user_data), signals[WORKSPACE_BACKDROP_CHANGED], 0, backdrop);
     }
 }
 
-- 
1.7.10.4