Added function to change screen focus by direction

The function awful.screen.focus_bydirection changes the screen focus
according to physical position. The code is based on
awful.client.focus.bydirection.

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

lib/awful/screen.lua.in

@@ -47,6 +47,23 @@ function screen.focus(_screen)
     capi.mouse.screen = _screen
 end
 
+--- Give the focus to a screen, and move pointer, by physical position relative to current screen.
+-- @param dir The direction, can be either "up", "down", "left" or "right".
+-- @param screen Screen number.
+function screen.focus_bydirection(dir, _screen)
+    local sel = _screen or capi.mouse.screen
+    if sel then
+        local geomtbl = {}
+        for s = 1, capi.screen.count() do
+            geomtbl[s] = capi.screen[s].geometry
+        end
+        local target = util.get_rectangle_in_direction(dir, geomtbl, capi.screen[sel].geometry)
+        if target then
+            return screen.focus(target)
+        end
+    end
+end
+
 --- Give the focus to a screen, and move pointer, but relative to the current
 -- focused screen.
 -- @param i Value to add to the current focused screen index. 1 will focus next

lib/awful/util.lua.in

@@ -260,6 +260,76 @@ function util.subsets(set)
     return ret
 end
 
+-- Return true whether rectangle B is in the right direction
+-- compared to rectangle A.
+-- @param dir The direction.
+-- @param gA The geometric specification for rectangle A.
+-- @param gB The geometric specification for rectangle B.
+-- @return True if B is in the direction of A.
+local function is_in_direction(dir, gA, gB)
+    if dir == "up" then
+        return gA.y > gB.y
+    elseif dir == "down" then
+        return gA.y < gB.y
+    elseif dir == "left" then
+        return gA.x > gB.x
+    elseif dir == "right" then
+        return gA.x < gB.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 screen and the left side of the checked screen.
+-- @param dir The direction.
+-- @param gA The first rectangle.
+-- @param gB The second rectangle.
+-- @return The distance between the screens.
+local function calculate_distance(dir, _gA, _gB)
+    local gA = _gA
+    local gB = _gB
+
+    if dir == "up" then
+        gB.y = gB.y + gB.height
+    elseif dir == "down" then
+        gA.y = gA.y + gA.height
+    elseif dir == "left" then
+        gB.x = gB.x + gB.width
+    elseif dir == "right" then
+        gA.x = gA.x + gA.width
+    end
+
+    return math.sqrt(math.pow(gB.x - gA.x, 2) + math.pow(gB.y - gA.y, 2))
+end
+
+-- Get the nearest rectangle in the given direction. Every rectangle is specified as a table
+-- with 'x', 'y', 'width', 'height' keys, the same as client or screen geometries.
+-- @param dir The direction, can be either "up", "down", "left" or "right".
+-- @param recttbl A table of rectangle specifications.
+-- @param cur The current rectangle.
+-- @return The index for the rectangle in recttbl closer to cur in the given direction. nil if none found.
+function util.get_rectangle_in_direction(dir, recttbl, cur)
+    local dist, dist_min
+    local target = nil
+
+    -- We check each object
+    for i, rect in ipairs(recttbl) do
+        -- Check geometry to see if object is located in the right direction.
+        if is_in_direction(dir, cur, rect) then
+            -- Calculate distance between current and checked object.
+            dist = calculate_distance(dir, cur, rect)
+
+            -- If distance is shorter then keep the object.
+            if not target or dist < dist_min then
+                target = i
+                dist_min = dist
+            end
+        end
+    end
+    return target
+end
+
 --- Join all tables given as parameters.
 -- This will iterate all tables and insert all their keys into a new table.
 -- @param args A list of tables to join