Support 'vertical' Workspace warping

'Vertical' Workspace warping is a variant of the existing Workspace
warping feature: When a user drags a window to the edge of the Screen,
the window is warped to the next / previous workspace.

'Vertical' Workspace warping detects a drag towards the upper / lower
border of the screen and warps the current workspace about an 'offset'.
Example given, lets say the user has 9 workspaces and considers them to
form a 3x3 grid:

  +-+-+-+
  |1|2|3|
  +-+-+-+
  |4|5|6|
  +-+-+-+
  |7|8|9|
  +-+-+-+

An 'offset' of 3 warps from workspaces 2 to workspace 5 (or 8), when a
window is dragged to the bottom / top border.

New configuration ressources:

    session.screenN.workspacewarpingvertical: true
    session.screenN.workspacewarpingverticaloffset: X

4 files changed, 58 insertions, 16 deletions

diff --git a/src/Screen.hh b/src/Screen.hh
index 30fbb4a..15eb349 100644
--- a/src/Screen.hh
+++ b/src/Screen.hh
@@ -95,6 +95,8 @@ public:
     bool isRootColormapInstalled() const { return root_colormap_installed; }
     bool isScreenManaged() const { return m_state.managed; }
     bool isWorkspaceWarping() const { return (m_workspaces_list.size() > 1) && *resource.workspace_warping; }
+    bool isWorkspaceWarpingVertical() const { return *resource.workspace_warping_vertical; }
+    int getWorkspaceWarpingVerticalOffset() const { return *resource.workspace_warping_vertical_offset; }
     bool doAutoRaise() const { return *resource.auto_raise; }
     bool clickRaises() const { return *resource.click_raises; }
     bool doOpaqueMove() const { return *resource.opaque_move; }
diff --git a/src/ScreenResource.cc b/src/ScreenResource.cc
index dbf532b..c188648 100644
--- a/src/ScreenResource.cc
+++ b/src/ScreenResource.cc
@@ -88,6 +88,8 @@ ScreenResource::ScreenResource(FbTk::ResourceManager& rm,
     max_disable_move(rm, false, scrname+".maxDisableMove", altscrname+".MaxDisableMove"),
     max_disable_resize(rm, false, scrname+".maxDisableResize", altscrname+".MaxDisableResize"),
     workspace_warping(rm, true, scrname+".workspacewarping", altscrname+".WorkspaceWarping"),
+    workspace_warping_vertical(rm, true, scrname+".workspacewarpingvertical", altscrname+".WorkspaceWarpingVertical"),
+    workspace_warping_vertical_offset(rm, 1, scrname+".workspacewarpingverticaloffset", altscrname+".WorkspaceWarpingVerticalOffset"),
     show_window_pos(rm, false, scrname+".showwindowposition", altscrname+".ShowWindowPosition"),
     auto_raise(rm, true, scrname+".autoRaise", altscrname+".AutoRaise"),
     click_raises(rm, true, scrname+".clickRaises", altscrname+".ClickRaises"),
diff --git a/src/ScreenResource.hh b/src/ScreenResource.hh
index 7f1e621..bc782e1 100644
--- a/src/ScreenResource.hh
+++ b/src/ScreenResource.hh
@@ -37,6 +37,7 @@ struct ScreenResource {
        max_disable_move,
        max_disable_resize,
        workspace_warping,
+       workspace_warping_vertical,
        show_window_pos,
        auto_raise,
        click_raises;
@@ -53,7 +54,8 @@ struct ScreenResource {
         menu_alpha,
         menu_delay,
         tab_width,
-        tooltip_delay;
+        tooltip_delay,
+       workspace_warping_vertical_offset;
     FbTk::Resource<bool> allow_remote_actions;
     FbTk::Resource<bool> clientmenu_use_pixmap;
     FbTk::Resource<bool> tabs_use_pixmap;
diff --git a/src/Window.cc b/src/Window.cc
index 23c9789..6714d0a 100644
--- a/src/Window.cc
+++ b/src/Window.cc
@@ -2539,6 +2539,10 @@ void FluxboxWindow::motionNotifyEvent(XMotionEvent &me) {
 
         // Warp to next or previous workspace?, must have moved sideways some
         int moved_x = me.x_root - m_last_resize_x;
+
+        // Warp to a workspace offset (if treating workspaces like a grid)
+        int moved_y = me.y_root - m_last_resize_y;
+
         // save last event point
         m_last_resize_x = me.x_root;
         m_last_resize_y = me.y_root;
@@ -2554,25 +2558,57 @@ void FluxboxWindow::motionNotifyEvent(XMotionEvent &me) {
             }
         }
 
-        if (moved_x && screen().isWorkspaceWarping()) {
+
+        // check for warping
+        //
+        // +--monitor-1--+--monitor-2---+
+        // |w            |             w|
+        // |w            |             w|
+        // +-------------+--------------+
+        //
+        // mouse-warping is enabled, the mouse needs to be in the "warp_pad"
+        // zone.
+        //
+        const int  warp_pad            = screen().getEdgeSnapThreshold();
+        const int  workspaces          = screen().numberOfWorkspaces();
+        const bool is_warping          = screen().isWorkspaceWarping();
+        const bool is_warping_vertical = screen().isWorkspaceWarpingVertical();
+
+        if ((moved_x || moved_y) && is_warping) {
             unsigned int cur_id = screen().currentWorkspaceID();
             unsigned int new_id = cur_id;
-            const int warpPad = screen().getEdgeSnapThreshold();
-            // 1) if we're inside the border threshold
-            // 2) if we moved in the right direction
-            if (me.x_root >= int(screen().width()) - warpPad - 1 &&
-                    moved_x > 0) {
-                //warp right
-                new_id = (cur_id + 1) % screen().numberOfWorkspaces();
-                m_last_resize_x = 0; // move mouse back to x=0
-            } else if (me.x_root <= warpPad &&
-                    moved_x < 0) {
-                //warp left
-                new_id = (cur_id + screen().numberOfWorkspaces() - 1) % screen().numberOfWorkspaces();
-                m_last_resize_x = screen().width() - 1; // move mouse to screen width - 1
+
+            // border threshold
+            int bt_right  = int(screen().width()) - warp_pad - 1;
+            int bt_left   = warp_pad;
+            int bt_top    = int(screen().height()) - warp_pad - 1;
+            int bt_bottom = warp_pad;
+
+            if (moved_x) {
+                if (me.x_root >= bt_right && moved_x > 0) { //warp right
+                    new_id          = (cur_id + 1) % workspaces;
+                    m_last_resize_x = 0;
+                } else if (me.x_root <= bt_left && moved_x < 0) { //warp left
+                    new_id          = (cur_id +  -1) % workspaces;
+                    m_last_resize_x = screen().width() - 1;
+                }
             }
-            if (new_id != cur_id) {
 
+            if (moved_y && is_warping_vertical) {
+
+                const int warp_offset = screen().getWorkspaceWarpingVerticalOffset();
+
+                if (me.y_root >= bt_top && moved_y > 0) { // warp down
+                    new_id          = (cur_id + warp_offset) % workspaces;
+                    m_last_resize_y = 0;
+                } else if (me.y_root <= bt_bottom && moved_y < 0) { // warp up
+                    new_id          = (cur_id + workspaces - warp_offset) % workspaces;
+                    m_last_resize_y = screen().height() - 1;
+                }
+            }
+
+            // if we are warping
+            if (new_id != cur_id) {
                 // remove motion events from queue to avoid repeated warps
                 while (XCheckTypedEvent(display, MotionNotify, &e)) {
                     // might as well update the y-coordinate