osc: make margins available

This is for console.lua (see next commit). The idea is that console.lua
can adjust its offset to the bottom of the window by the height of the
OSC.

If the OSC is not set to permanently visible, export no margins, because
it would look weird to move the console depending on the mouse movement.

player/lua/osc.lua

@@ -2058,6 +2058,7 @@ function osc_init()
         reset_margins()
     end
 
+    update_margins()
 end
 
 function reset_margins()
@@ -2069,6 +2070,24 @@ function reset_margins()
     end
 end
 
+function update_margins()
+    local margins = osc_param.video_margins
+
+    -- Don't report margins if it's visible only temporarily. At least for
+    -- console.lua this makes no sense.
+    if (not state.osc_visible) or (user_opts.hidetimeout >= 0) then
+        margins = {l = 0, r = 0, t = 0, b = 0}
+    end
+
+    utils.shared_script_property_set("osc-margins",
+        string.format("%f,%f,%f,%f", margins.l, margins.r, margins.t, margins.b))
+end
+
+function shutdown()
+    reset_margins()
+    utils.shared_script_property_set("osc-margins", nil)
+end
+
 --
 -- Other important stuff
 --
@@ -2110,6 +2129,7 @@ end
 function osc_visible(visible)
     state.osc_visible = visible
     control_timer()
+    update_margins()
 end
 
 function pause_state(name, enabled)
@@ -2478,7 +2498,7 @@ end
 
 validate_user_opts()
 
-mp.register_event("shutdown", reset_margins)
+mp.register_event("shutdown", shutdown)
 mp.register_event("start-file", request_init)
 mp.register_event("tracks-changed", request_init)
 mp.observe_property("playlist", nil, request_init)
@@ -2609,6 +2629,8 @@ function visibility_mode(mode, no_osd)
     if not no_osd and tonumber(mp.get_property("osd-level")) >= 1 then
         mp.osd_message("OSC visibility: " .. mode)
     end
+
+    update_margins()
 end
 
 visibility_mode(user_opts.visibility, true)