osc: use new overlay API

This tries to avoid the update() call if nothing changed. This brings it
more into line with the old code (the osd-overlay command simply does
not skip the update if nothing changed). I don't know whether this
matters; most likely not. Normally, code should try to avoid redundant
updates on its own, so it's not the job of the command. However, for the
OSC we simply want to reduce the differences.

player/lua/osc.lua

@@ -116,6 +116,7 @@ local state = {
     using_video_margins = false,
     border = true,
     maximized = false,
+    osd = mp.create_osd_overlay("ass-events"),
 }
 
 local window_control_box_width = 80
@@ -127,6 +128,18 @@ local is_december = os.date("*t").month == 12
 -- Helperfunctions
 --
 
+function set_osd(res_x, res_y, text)
+    if state.osd.res_x == res_x and
+       state.osd.res_y == res_y and
+       state.osd.data == text then
+        return
+    end
+    state.osd.res_x = res_x
+    state.osd.res_y = res_y
+    state.osd.data = text
+    state.osd:update()
+end
+
 local margins_opts = {
     {"l", "video-margin-ratio-left"},
     {"r", "video-margin-ratio-right"},
@@ -2180,7 +2193,7 @@ end
 
 function render_wipe()
     msg.trace("render_wipe()")
-    mp.set_osd_ass(0, 0, "{}")
+    state.osd:remove()
 end
 
 function render()
@@ -2329,8 +2342,8 @@ function render()
     end
 
     -- submit
-    mp.set_osd_ass(osc_param.playresy * osc_param.display_aspect,
-                   osc_param.playresy, ass.text)
+    set_osd(osc_param.playresy * osc_param.display_aspect,
+            osc_param.playresy, ass.text)
 end
 
 --
@@ -2466,7 +2479,7 @@ function tick()
         ass:pos(320, icon_y+65)
         ass:an(8)
         ass:append("Drop files or URLs to play here.")
-        mp.set_osd_ass(640, 360, ass.text)
+        set_osd(640, 360, ass.text)
 
         if state.showhide_enabled then
             mp.disable_key_bindings("showhide")
@@ -2482,7 +2495,7 @@ function tick()
         render()
     else
         -- Flush OSD
-        mp.set_osd_ass(osc_param.playresy, osc_param.playresy, "")
+        set_osd(osc_param.playresy, osc_param.playresy, "")
     end
 
     state.tick_last_time = mp.get_time()