osc.lua: add option to make rendering smoother

OSC rendering used to be smooth (up to OSD rendering fps) before
48f906249e, but after that commit the
frame duration is hardcoded to 30 ms. This is too high and results in
choppy OSC rendering, which is very noticeable with the progress bar
while moving mouse over it or playing a short 60 fps video.

This makes the duration an option so that it can be decreased to make
OSC rendering smoother.

DOCS/man/osc.rst

@@ -472,6 +472,12 @@ Configurable Options
 
     Sets the colors of the elements that are being pressed or held down.
 
+``tick_delay``
+    Default: 1/60
+
+    Sets the minimum interval between OSC redraws in seconds. This can be
+    decreased on fast systems to make OSC rendering smoother.
+
 
 Script Commands
 ~~~~~~~~~~~~~~~

player/lua/osc.lua

@@ -69,7 +69,9 @@ local user_opts = {
     top_buttons_color = "#FFFFFF",	-- color of top buttons
     held_element_color = "#999999",	-- color of an element while held down
 
-    time_pos_outline_color = "#000000"	-- color of the border timecodes in slimbox and TimePosBar
+    time_pos_outline_color = "#000000",	-- color of the border timecodes in slimbox and TimePosBar
+
+    tick_delay = 1 / 60,                  -- minimum interval between OSC redraws in seconds
 }
 
 local osc_param = { -- calculated by osc_init()
@@ -90,7 +92,7 @@ local margins_opts = {
     {"b", "video-margin-ratio-bottom"},
 }
 
-local tick_delay = 0.03
+local tick_delay = 1 / 60
 local tracks_osc = {}
 local tracks_mpv = {}
 local window_control_box_width = 80
@@ -2980,6 +2982,7 @@ end
 opt.read_options(user_opts, "osc", function()
     validate_user_opts()
     set_osc_styles()
+    tick_delay = user_opts.tick_delay
     request_tick()
     visibility_mode(user_opts.visibility, true)
     update_duration_watch()