FS#996: awful.ewmh: Connect to property::border_width signal

For example, I have some lua code which sets the border width based on the
number of visible clients. When just a single client is visible, the border
width is 0, else it's what the theme says.

Previously, this caused visible "glitches" for fullscreen'd and maximized
clients. This patch fixes that and updates the client's geometry and
border width appropriately.

This has a slight chance of going into an endless loop if someone sets a
fullscreen'd clients border width from its property::border_width signal.
Just don't do that!

Thanks to Arvydas Sidorenko for finding this issue.

Signed-off-by: Uli Schlachter <psychon@znc.in>

lib/awful/ewmh.lua.in

@@ -112,9 +112,29 @@ local function screen_change(window)
     end
 end
 
+-- Update a client's settings when its border width changes
+local function border_change(window)
+    -- Fix up the geometry in case this window needs to cover the whole screen.
+    local bw = window.border_width or 0
+    local g = screen[window.screen].workarea
+    if window.maximized_vertical then
+        window:geometry { height = g.height - 2*bw, y = g.y }
+    end
+    if window.maximized_horizontal then
+        window:geometry { height = g.height - 2*bw, y = g.y }
+    end
+    if window.fullscreen then
+        -- This *will* cause an endless loop if some other property::border_width
+        -- signal dares to change the border width, too, so don't do that!
+        window.border_width = 0
+        window:geometry(screen[window.screen].geometry)
+    end
+end
+
 client.connect_signal("request::maximized_horizontal", maximized_horizontal)
 client.connect_signal("request::maximized_vertical", maximized_vertical)
 client.connect_signal("request::fullscreen", fullscreen)
 client.connect_signal("property::screen", screen_change)
+client.connect_signal("property::border_width", border_change)
 
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