awful: add focusbydirection() (FS#166)

Signed-off-by: Julien Danjou <julien@danjou.info>

lib/awful.lua.in

@@ -13,6 +13,7 @@ local pairs = pairs
 local unpack = unpack
 local os = os
 local io = io
+local math = math
 local setmetatable = setmetatable
 local table = table
 local capi =
@@ -169,6 +170,87 @@ function client.next(i, c)
     end
 end
 
+--- Return true whether client B is in the right direction
+-- compared to client A.
+-- @param dir The direction.
+-- @param cA The first client.
+-- @param cB The second client.
+-- @return True if B is in the direction of A.
+local function is_in_direction(dir, cA, cB)
+    if dir == "up" then
+        return cA['y'] > cB['y']
+    elseif dir == "down" then
+        return cA['y'] < cB['y']
+    elseif dir == "left" then
+        return cA['x'] > cB['x']
+    elseif dir == "right" then
+        return cA['x'] < cB['x']
+    end
+    return false
+end
+
+--- Calculate distance between two points.
+-- i.e: if we want to move to the right, we will take the right border
+-- of the currently focused client and the left side of the checked client.
+-- This avoid the focus of an upper client when you move to the right in a
+-- tilebottom layout with nmaster=2 and 5 clients open, for instance.
+-- @param dir The direction.
+-- @param cA The first client.
+-- @param cB The second client.
+-- @return The distance between the clients.
+local function calculate_distance(dir, cA, cB)
+    local xA = cA['x']
+    local xB = cB['x']
+    local yA = cA['y']
+    local yB = cB['y']
+
+    if dir == "up" then
+        yB = yB + cB['height']
+    elseif dir == "down" then
+        yA = yA + cA['height']
+    elseif dir == "left" then
+        xB = xB + cB['width']
+    elseif dir == "right" then
+        xA = xA + cA['width']
+    end
+
+    return math.sqrt(math.pow(xB - xA, 2) + math.pow(yB - yA, 2))
+end
+
+--- Focus a client by the given direction.
+-- @param dir The direction, can be either "up", "down", "left" or "right".
+-- @param c Optional client.
+function client.focusbydirection(dir, c)
+    local sel = c or capi.client.focus_get()
+    if sel then
+        local coords = sel.coords
+        local dist, dist_min
+        local target = nil
+        local cls = capi.client.visible_get(sel.screen)
+
+        -- We check each client.
+        for i, c in ipairs(cls) do
+            -- Check coords to see if client is located in the right direction.
+            if is_in_direction(dir, coords, c.coords) then
+
+                -- Calculate distance between focused client and checked client.
+                dist = calculate_distance(dir, coords, c.coords)
+
+                -- If distance is shorter then keep the client.
+                if not target or dist < dist_min then
+                    target = c
+                    dist_min = dist
+                end
+            end
+        end
+
+        -- If we found a client to focus, then do it.
+        if target then
+            target:focus_set()
+        end
+    end
+end
+
 --- Focus a client by its relative index.
 -- @param i The index.
 -- @param c Optional client.