osc.lua: use dedicated 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 option.

DOCS/man/options.rst

@@ -3134,6 +3134,16 @@ Subtitles
 
     Default: 34
 
+``--sub-margin-y-offset=<size>``
+    Additional vertical offset added to the subtitle margin, in scaled pixels.
+    This is added on top of ``--sub-margin-y``.
+
+    This is intended for dynamic margin adjustments at runtime (e.g. by
+    scripts like the OSC to avoid subtitle/UI overlap). For persistent
+    settings, use ``--sub-margin-y`` instead.
+
+    Default: 0
+
 ``--sub-align-x=<left|center|right>``
     Control to which corner of the screen text subtitles should be
     aligned to (default: ``center``).
@@ -4816,6 +4826,16 @@ OSD
 
     Default: 16
 
+``--osd-margin-y-offset=<size>``
+    Additional vertical offset added to the OSD margin, in scaled pixels.
+    This is added on top of ``--osd-margin-y``.
+
+    This is intended for dynamic margin adjustments at runtime (e.g. by
+    scripts like the OSC to avoid OSD/UI overlap). For persistent settings,
+    use ``--osd-margin-y`` instead.
+
+    Default: 0
+
 ``--osd-align-x=<left|center|right>``
     Control to which corner of the screen OSD should be
     aligned to (default: ``left``).

DOCS/man/osc.rst

@@ -412,10 +412,9 @@ 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. Uses ``--sub-margin-y-offset`` to apply the adjustment.
 
     With ``boxvideo`` enabled and ``--sub-use-margins=no``, subtitles are
     already confined to the video area and this option has no additional
@@ -424,11 +423,9 @@ 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. Uses ``--osd-margin-y-offset`` to apply the adjustment.
 
 ``windowcontrols``
     Default: auto (Show window controls if there is no window border/title-bar)

player/lua/osc.lua

@@ -544,18 +544,6 @@ 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
@@ -563,8 +551,8 @@ local function reset_margins()
         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()
@@ -618,8 +606,8 @@ 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)},
     {"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;