osc.lua: use private options to control SUB/OSD offset

There is concern that with certain user options or script the value of
`{sub,osd}-margin-y` value may be persisted or overwrite user option
when it's changed while OSD is visible and offset is applied.

Fix this by using dedicated private option only for OSC use.

Author: kasper93

DOCS/man/osc.rst

@@ -411,10 +411,9 @@ Configurable Options
 ``sub_margins``
     Default: yes
 
-    Whether to adjust ``--sub-margin-y`` so that subtitles do not overlap
-    with the OSC. The offset is derived from the bottom OSC margin and added
-    on top of the current ``--sub-margin-y`` value. Requires
-    ``dynamic_margins`` or ``visibility=always`` to take effect.
+    Whether to adjust the subtitle margin so that subtitles do not overlap
+    with the OSC. Requires ``dynamic_margins`` or ``visibility=always`` to
+    take effect.
 
     With ``boxvideo`` enabled and ``--sub-use-margins=no``, subtitles are
     already confined to the video area and this option has no additional
@@ -423,11 +422,9 @@ Configurable Options
 ``osd_margins``
     Default: yes
 
-    Whether to adjust ``--osd-margin-y`` so that OSD text does not overlap
-    with the OSC. The offset is derived from the top OSC margin (including
-    window controls when present) and added on top of the current
-    ``--osd-margin-y`` value. Requires ``dynamic_margins`` or
-    ``visibility=always`` to take effect.
+    Whether to adjust the OSD margin so that OSD text does not overlap
+    with the OSC. Requires ``dynamic_margins`` or ``visibility=always`` to
+    take effect.
 
 ``windowcontrols``
     Default: auto (Show window controls if there is no window border)

player/lua/osc.lua

@@ -543,27 +543,15 @@ local function cache_enabled()
     return state.cache_state and #state.cache_state["seekable-ranges"] > 0
 end
 
-local function set_margin_offset(prop, offset)
-    if offset > 0 then
-        if not state[prop] then
-            state[prop] = mp.get_property_number(prop)
-        end
-        mp.set_property_number(prop, state[prop] + offset)
-    elseif state[prop] then
-        mp.set_property_number(prop, state[prop])
-        state[prop] = nil
-    end
-end
-
 local function reset_margins()
     if state.using_video_margins then
         for _, mopt in ipairs(margins_opts) do
             mp.set_property_number(mopt[2], 0.0)
         end
         state.using_video_margins = false
     end
-    set_margin_offset("sub-margin-y", 0)
-    set_margin_offset("osd-margin-y", 0)
+    mp.set_property_number("sub-margin-y-offset", 0)
+    mp.set_property_number("osd-margin-y-offset", 0)
 end
 
 local function update_margins()
@@ -617,8 +605,8 @@ local function update_margins()
         end
         return margin * osc_param.playresy
     end
-    set_margin_offset("sub-margin-y", get_margin("sub"))
-    set_margin_offset("osd-margin-y", get_margin("osd"))
+    mp.set_property_number("sub-margin-y-offset", get_margin("sub"))
+    mp.set_property_number("osd-margin-y-offset", get_margin("osd"))
 
     mp.set_property_native("user-data/osc/margins", margins)
 end

sub/ass_mp.c

@@ -64,7 +64,7 @@ void mp_ass_set_style(ASS_Style *style, double res_y,
     style->Spacing = opts->spacing * scale;
     style->MarginL = opts->margin_x * scale;
     style->MarginR = style->MarginL;
-    style->MarginV = opts->margin_y * scale;
+    style->MarginV = (opts->margin_y + opts->margin_y_offset) * scale;
     style->ScaleX = 1.;
     style->ScaleY = 1.;
     style->Alignment = 1 + (opts->align_x + 1) + (opts->align_y + 2) % 3 * 4;

sub/osd.c

@@ -60,6 +60,7 @@ static const m_option_t style_opts[] = {
     {"spacing", OPT_FLOAT(spacing), M_RANGE(-10, 10)},
     {"margin-x", OPT_INT(margin_x), M_RANGE(0, INT_MAX)},
     {"margin-y", OPT_INT(margin_y), M_RANGE(0, INT_MAX)},
+    {"margin-y-offset", OPT_INT(margin_y_offset), .flags = M_OPT_PRIVATE},
     {"align-x", OPT_CHOICE(align_x,
         {"left", -1}, {"center", 0}, {"right", +1})},
     {"align-y", OPT_CHOICE(align_y,

sub/osd.h

@@ -155,6 +155,7 @@ struct osd_style_opts {
     float spacing;
     int margin_x;
     int margin_y;
+    int margin_y_offset;
     int align_x;
     int align_y;
     float blur;