awful.screen: Add a method to apply various paddings.

This avoid code duplications.

lib/awful/screen.lua

@@ -30,6 +30,19 @@ data.padding = {}
 
 screen.mouse_per_screen = {}
 
+--- Take an input geometry and substract/add a delta
+-- @tparam table geo A geometry (width, height, x, y) table
+-- @tparam table delta A delata table (top, bottom, x, y)
+-- @treturn table A geometry (width, height, x, y) table
+local function apply_geometry_ajustments(geo, delta)
+    return {
+        x      = geo.x      + (delta.left or 0),
+        y      = geo.y      + (delta.top  or 0),
+        width  = geo.width  - (delta.left or 0) - (delta.right  or 0),
+        height = geo.height - (delta.top  or 0) - (delta.bottom or 0),
+    }
+end
+
 -- @param s Screen
 -- @param x X coordinate of point
 -- @param y Y coordinate of point
@@ -173,6 +186,53 @@ function screen.focused()
     return capi.mouse.screen
 end
 
+--- Get a placement bounding geometry.
+-- This method compute different variants of the "usable" screen geometry.
+--
+-- Valid arguments are:
+--
+-- * **honor_padding**: Honor the screen padding.
+-- * **honor_workarea**: Honor the screen workarea
+-- * **margins**: Apply some margins on the output. This can wither be a number
+--    or a table with *left*, *right*, *top* and *bottom* keys.
+-- * **tag**: Use the tag screen instead of `s`
+-- * **parent**: A parent drawable to use a base geometry
+-- * **bounding_rect**: A bounding rectangle. This parameter is incompatible with
+--    `honor_workarea`.
+--
+-- @tparam[opt=mouse.screen] screen s A screen
+-- @tparam[opt={}] table args The arguments
+-- @treturn table A table with *x*, *y*, *width* and *height*.
+function screen.get_bounding_geometry(s, args)
+    args = args or {}
+
+    -- If the tag has a geometry, assume it is right
+    if args.tag then
+        s = args.tag.screen
+    end
+
+    s = get_screen(s or capi.mouse.screen)
+
+    local geo = args.bounding_rect or (args.parent and args.parent:geometry()) or
+        s[args.honor_workarea and "workarea" or "geometry"]
+
+    if (not args.parent) and (not args.bounding_rect) and args.honor_padding then
+        local padding = screen.padding(s)
+        geo = apply_geometry_ajustments(geo, padding)
+    end
+
+    if args.margins then
+        geo = apply_geometry_ajustments(geo,
+            type(args.margins) == "table" and args.margins or {
+                left = args.margins, right  = args.margins,
+                top  = args.margins, bottom = args.margins,
+            }
+        )
+    end
+
+    return geo
+end
+
 capi.screen.add_signal("padding")
 
 return screen