Allow dragging tiled windows with the mouse. (#3085)

Fixes #2643

Inner drop region behaves like move to mark.
The outer region is close to the edge (currently 30px from the edge).
This will place the container as a sibling in the given direction within
the parent container. If the move direction goes against the orientation
of the parent container, tree_move() is called.

Contributors:
Co-authored-by: Orestis Floros <orestisflo@gmail.com>
See #3085
- Inner drop region behaves like move to mark
- Handle workspaces
- Fix crash when target closes
- Initiate tiling drag from titlebar
- Hide indicator until container is dragged outside of original position
- Calculate outer_threshold using percentages instead of fixed pixel
values
- Emit 'move' event properly
- Don't focus previously unfocused containers
- Use tree_split() on different orientation
- Fix redundant split containers
- DT_PARENT
- Readability & optimizations
- Limit parent threshold by render_deco_height()
- Tests
- Fullscreen container handling
- Initiate drag from title bar
- Fix issue of EnterNotify events still triggering after drag_callback
  is called
- Include decorations for drop target calculation

Co-authored-by: Michael Forster <email@michael-forster.de>
See #2178
- Original implementation of tiling drag + indicator window
> A container can be dragged by the title bar to one of the four sides
> of another container. That container will then be split either
> horizontally or vertically.

Co-authored-by: Tony Crisci <tony@dubstepdish.com>
See #2653
- Original implementation of outer/inner drop region indicator:
> There are two drop regions per direction.
>
> The inner region is closer to the center of the window. Dropping on
> this region will split the target container and put the container
> within the split at the given direction beside the target container.
>
> The outer region is close to the edge (currently 30px from the edge).
> This will place the container as a sibling in the given direction within
> the parent container.
>
> Dropping into the outer region moves the con beside the target. If the
> move direction goes against the orientation of the parent container, the
> con moves out of the row.
- Fix crash: Ignore containers without a managed window (eg i3bar)

src/click.c

@@ -188,9 +188,6 @@ static void route_click(Con *con, xcb_button_press_event_t *event, const bool mo
             goto done;
     }
 
-    if (ws != focused_workspace)
-        workspace_show(ws);
-
     /* get the floating con */
     Con *floatingcon = con_inside_floating(con);
     const bool proportional = (event->state & XCB_KEY_BUT_MASK_SHIFT) == XCB_KEY_BUT_MASK_SHIFT;
@@ -218,7 +215,13 @@ static void route_click(Con *con, xcb_button_press_event_t *event, const bool mo
         goto done;
     }
 
-    /* 2: focus this con or one of its children. */
+    /* 2: floating modifier pressed, initiate a drag */
+    if (mod_pressed && event->detail == XCB_BUTTON_INDEX_1 && !floatingcon) {
+        tiling_drag(con, event);
+        goto done;
+    }
+
+    /* 3: focus this con or one of its children. */
     Con *con_to_focus = con;
     if (in_stacked && dest == CLICK_DECORATION) {
         /* If the container is a tab/stacked container and the click happened
@@ -231,19 +234,22 @@ static void route_click(Con *con, xcb_button_press_event_t *event, const bool mo
             }
         }
     }
+    if (ws != focused_workspace) {
+        workspace_show(ws);
+    }
     con_activate(con_to_focus);
 
-    /* 3: For floating containers, we also want to raise them on click.
+    /* 4: For floating containers, we also want to raise them on click.
      * We will skip handling events on floating cons in fullscreen mode */
     Con *fs = con_get_fullscreen_covering_ws(ws);
     if (floatingcon != NULL && fs != con) {
-        /* 4: floating_modifier plus left mouse button drags */
+        /* 5: floating_modifier plus left mouse button drags */
         if (mod_pressed && is_left_click) {
             floating_drag_window(floatingcon, event, false);
             return;
         }
 
-        /*  5: resize (floating) if this was a (left or right) click on the
+        /*  6: resize (floating) if this was a (left or right) click on the
          * left/right/bottom border, or a right click on the decoration.
          * also try resizing (tiling) if possible */
         if (mod_pressed && is_right_click) {
@@ -272,7 +278,7 @@ static void route_click(Con *con, xcb_button_press_event_t *event, const bool mo
             return;
         }
 
-        /* 6: dragging, if this was a click on a decoration (which did not lead
+        /* 7: dragging, if this was a click on a decoration (which did not lead
          * to a resize) */
         if (dest == CLICK_DECORATION && is_left_click) {
             floating_drag_window(floatingcon, event, !was_focused);
@@ -282,7 +288,13 @@ static void route_click(Con *con, xcb_button_press_event_t *event, const bool mo
         goto done;
     }
 
-    /* 7: floating modifier pressed, initiate a resize */
+    /* 8: floating modifier pressed, initiate a drag */
+    if ((mod_pressed || dest == CLICK_DECORATION) && event->detail == XCB_BUTTON_INDEX_1) {
+        tiling_drag(con, event);
+        goto done;
+    }
+
+    /* 9: floating modifier pressed, initiate a resize */
     if (dest == CLICK_INSIDE && mod_pressed && is_right_click) {
         if (floating_mod_on_tiled_client(con, event)) {
             return;
@@ -293,7 +305,7 @@ static void route_click(Con *con, xcb_button_press_event_t *event, const bool mo
         xcb_flush(conn);
         return;
     }
-    /* 8: otherwise, check for border/decoration clicks and resize */
+    /* 10: otherwise, check for border/decoration clicks and resize */
     if ((dest == CLICK_BORDER || dest == CLICK_DECORATION) &&
         is_left_or_right_click) {
         DLOG("Trying to resize (tiling)\n");