commit 082f3dc0e53d4db1b6a990f0a23a18d358bc1b45
Author: Harald Judt <h.judt@gmx.at>
Date:   Mon Mar 11 20:05:35 2013 +0100

    Pager: Add viewport switching support (for compiz and alike).

diff --git a/plugins/pager/pager.c b/plugins/pager/pager.c
index 6f0a378..0f9b6c3 100644
--- a/plugins/pager/pager.c
+++ b/plugins/pager/pager.c
@@ -251,26 +251,77 @@ pager_plugin_scroll_event (GtkWidget      *widget,
   if (plugin->scrolling == FALSE)
     return TRUE;
 
-  active_ws = wnck_screen_get_active_workspace (plugin->wnck_screen);
-  active_n = wnck_workspace_get_number (active_ws);
-
-  if (event->direction == GDK_SCROLL_UP
-      || event->direction == GDK_SCROLL_LEFT)
-    active_n--;
+  if (n_workspaces == 0)
+    {
+      /* do we have only one workspace or are we in viewport mode (compiz) */
+      active_ws = wnck_screen_get_active_workspace (plugin->wnck_screen);
+      if (wnck_workspace_is_virtual (active_ws))
+        {
+	/* viewport mode */
+        int viewport_x;
+        int viewport_y;
+        int screen_width, screen_height;
+        int workspace_width, workspace_height;
+        int scroll_direction;
+
+        /* total workspacesize, e.g. 5120x1024 (5120=4x1280) */
+        workspace_width  = wnck_workspace_get_width  (active_ws);
+        workspace_height = wnck_workspace_get_height (active_ws);
+        /* current screensize, e.g. 1280x1024 */
+        screen_width  = wnck_screen_get_width  (plugin->wnck_screen);
+        screen_height = wnck_screen_get_height (plugin->wnck_screen);
+        /* current viewportcoordinates, e.g. 0,0 or 1280,0 */
+        viewport_x = wnck_workspace_get_viewport_x (active_ws);
+        viewport_y = wnck_workspace_get_viewport_y (active_ws);
+
+        switch (event->direction)
+          {
+            case GDK_SCROLL_UP:
+            case GDK_SCROLL_LEFT:
+              scroll_direction = +1;
+                break;
+            case GDK_SCROLL_DOWN:
+            case GDK_SCROLL_RIGHT:
+              scroll_direction = -1;
+                break;
+            default:
+                break;
+          }
+        /* viewportscroll is only in x-direction */
+        viewport_x = viewport_x + (scroll_direction * screen_width);
+
+        /* wrap if needed */
+        if (viewport_x > workspace_width)
+            viewport_x = 0;
+        if (viewport_x < 0)
+            viewport_x = workspace_width - screen_width;
+
+        wnck_screen_move_viewport (plugin->wnck_screen,
+                                  viewport_x, viewport_y);
+      }
+    }
   else
-    active_n++;
-
-  /* wrap around */
-  n_workspaces = wnck_screen_get_workspace_count (plugin->wnck_screen) - 1;
-  if (active_n < 0)
-    active_n = n_workspaces;
-  else if (active_n > n_workspaces)
-    active_n = 0;
-
-  new_ws = wnck_screen_get_workspace (plugin->wnck_screen, active_n);
-  if (new_ws != NULL && active_ws != new_ws)
-    wnck_workspace_activate (new_ws, event->time);
-
+    {
+      /* real workspaces */
+      active_ws = wnck_screen_get_active_workspace (plugin->wnck_screen);
+      active_n = wnck_workspace_get_number (active_ws);
+
+      if (event->direction == GDK_SCROLL_UP
+          || event->direction == GDK_SCROLL_LEFT)
+        active_n = active_n + 1;
+      else
+        active_n = active_n - 1;
+
+      /* wrap around */
+      if (active_n < 0)
+        active_n = n_workspaces;
+      else if (active_n > n_workspaces)
+        active_n = 0;
+
+      new_ws = wnck_screen_get_workspace (plugin->wnck_screen, active_n);
+      if (new_ws != NULL && active_ws != new_ws)
+        wnck_workspace_activate (new_ws, event->time);
+    }
   return TRUE;
 }