positioning.lua: add this script

This script provides script messages and bindings to pan videos and
images, making mpv a better image viewer out of the box.

DOCS/man/mpv.rst

@@ -1461,6 +1461,8 @@ works like in older mpv releases:
 
 .. include:: console.rst
 
+.. include:: positioning.rst
+
 .. include:: lua.rst
 
 .. include:: javascript.rst

DOCS/man/options.rst

@@ -1067,6 +1067,10 @@ Program Behavior
     Enable the builtin script that lets you select from lists of items (default:
     yes). By default, its keybindings start with the ``g`` key.
 
+``--load-positioning=<yes|no>``
+    Enable the builtin script that provides various keybindings to pan videos
+    and images (default: yes).
+
 ``--player-operation-mode=<cplayer|pseudo-gui>``
     For enabling "pseudo GUI mode", which means that the defaults for some
     options are changed. This option should not normally be used directly, but

DOCS/man/positioning.rst

@@ -0,0 +1,36 @@
+POSITIONING
+===========
+
+This script provides key bindings to pan videos and images.
+
+Script messages and bindings
+----------------------------
+
+``pan <axis> <amount>``
+    Adjust ``--video-align-x`` or ``--video-align-y`` relatively to the OSD
+    sizes, rather than relatively to the video sizes like the options. This is
+    useful to pan large images consistently.
+
+    ``axis`` can be ``x`` or ``y``, and ``amount`` is a number such that an
+    amount of 1 scrolls as much as the OSD width or height.
+
+``drag-to-pan``
+    Pan the video while holding a mouse button, relatively to the clicked point in
+    the OSD.
+
+``align-to-cursor``
+    Pan the video while holding a mouse button, relatively to the whole video.
+
+``cursor-centric-zoom <zoom>``
+    Increase ``--video-zoom`` by ``zoom`` and adjust ``--video-align-x`` and
+    ``--video-align-y`` to shift the OSD towards the position hovered by the
+    cursor, or the average position of touch points if known.
+
+Configurable Options
+~~~~~~~~~~~~~~~~~~~~
+
+``suppress_osd``
+    Default: no
+
+    Whether to not print the new value of ``--video-zoom`` when using
+    ``cursor-centric-zoom``.

options/options.c

@@ -588,6 +588,7 @@ static const m_option_t mp_opts[] = {
         OPT_CHOICE(lua_load_auto_profiles, {"no", 0}, {"yes", 1}, {"auto", -1}),
         .flags = UPDATE_BUILTIN_SCRIPTS},
     {"load-select", OPT_BOOL(lua_load_select), .flags = UPDATE_BUILTIN_SCRIPTS},
+    {"load-positioning", OPT_BOOL(lua_load_positioning), .flags = UPDATE_BUILTIN_SCRIPTS},
 #endif
 
 // ------------------------- stream options --------------------
@@ -1009,6 +1010,7 @@ static const struct MPOpts mp_default_opts = {
     .lua_load_console = true,
     .lua_load_auto_profiles = -1,
     .lua_load_select = true,
+    .lua_load_positioning = true,
 #endif
     .auto_load_scripts = true,
     .loop_times = 1,

options/options.h

@@ -186,6 +186,7 @@ typedef struct MPOpts {
     bool lua_load_console;
     int lua_load_auto_profiles;
     bool lua_load_select;
+    bool lua_load_positioning;
 
     bool auto_load_scripts;
 

player/core.h

@@ -440,7 +440,7 @@ typedef struct MPContext {
 
     struct mp_ipc_ctx *ipc_ctx;
 
-    int64_t builtin_script_ids[6];
+    int64_t builtin_script_ids[7];
 
     mp_mutex abort_lock;
 

player/lua.c

@@ -84,6 +84,9 @@ static const char * const builtin_lua_scripts[][2] = {
     },
     {"@select.lua",
 #   include "player/lua/select.lua.inc"
+    },
+    {"@positioning.lua",
+#   include "player/lua/positioning.lua.inc"
     },
     {0}
 };

player/lua/meson.build

@@ -1,6 +1,6 @@
 lua_files = ['defaults.lua', 'assdraw.lua', 'options.lua', 'osc.lua',
              'ytdl_hook.lua', 'stats.lua', 'console.lua', 'auto_profiles.lua',
-             'input.lua', 'fzy.lua', 'select.lua']
+             'input.lua', 'fzy.lua', 'select.lua', 'positioning.lua']
 foreach file: lua_files
     lua_file = custom_target(file,
         input: file,

player/lua/positioning.lua

@@ -0,0 +1,119 @@
+--[[
+This file is part of mpv.
+
+mpv is free software; you can redistribute it and/or
+modify it under the terms of the GNU Lesser General Public
+License as published by the Free Software Foundation; either
+version 2.1 of the License, or (at your option) any later version.
+
+mpv is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU Lesser General Public License for more details.
+
+You should have received a copy of the GNU Lesser General Public
+License along with mpv.  If not, see <http://www.gnu.org/licenses/>.
+]]
+
+local options = {
+    suppress_osd = false,
+}
+
+require "mp.options".read_options(options)
+
+mp.register_script_message("pan", function (axis, amount)
+    local dims = mp.get_property_native("osd-dimensions")
+    local dimension = axis == "x" and dims.w - dims.ml - dims.mr or dims.h - dims.mt - dims.mb
+    local osd_dimension = axis == "x" and dims.w or dims.h
+    -- 1 video-align shifts the OSD by (dimension - osd_dimension) / 2 pixels,
+    -- so the equation to find how much video-align to add to offset the OSD by
+    -- osd_dimension is:
+    -- x/1 = osd_dimension / ((dimension - osd_dimension) / 2)
+    if dimension ~= osd_dimension then
+        mp.commandv("add", "video-align-" .. axis,
+                    amount * 2 * osd_dimension / (dimension - osd_dimension))
+    end
+end)
+
+mp.add_key_binding(nil, "drag-to-pan", function (t)
+    if t.event == "up" then
+        mp.remove_key_binding("drag-to-pan-mouse-move")
+        return
+    end
+
+    local dims = mp.get_property_native("osd-dimensions")
+    local old_mouse_pos = mp.get_property_native("mouse-pos")
+    local old_align_x = mp.get_property_native("video-align-x")
+    local old_align_y = mp.get_property_native("video-align-y")
+
+    mp.add_forced_key_binding("MOUSE_MOVE", "drag-to-pan-mouse-move", function()
+        local mouse_pos = mp.get_property_native("mouse-pos")
+        -- 1 video-align shifts the OSD by (dimension - osd_dimension) / 2 pixels,
+        -- so the equation to find how much video-align to add to offset the OSD
+        -- by the difference in mouse position is:
+        -- x/1 = (mouse_pos - old_mouse_pos) / ((dimension - osd_dimension) / 2)
+        local align = old_align_x + 2 * (mouse_pos.x - old_mouse_pos.x)
+                      / (dims.ml + dims.mr)
+        mp.set_property("video-align-x", math.min(1, math.max(align, -1)))
+        align = old_align_y + 2 * (mouse_pos.y - old_mouse_pos.y)
+                / (dims.mt + dims.mb)
+        mp.set_property("video-align-y", math.min(1, math.max(align, -1)))
+    end)
+end, { complex = true })
+
+mp.add_key_binding(nil, "align-to-cursor", function (t)
+    if t.event == "up" then
+        mp.remove_key_binding("align-to-cursor-mouse-move")
+        return
+    end
+
+    local dims = mp.get_property_native("osd-dimensions")
+    mp.add_forced_key_binding("MOUSE_MOVE", "align-to-cursor-mouse-move", function()
+        local mouse_pos = mp.get_property_native("mouse-pos")
+        mp.set_property("video-align-x", (mouse_pos.x * 2 - dims.w) / dims.w)
+        mp.set_property("video-align-y", (mouse_pos.y * 2 - dims.h) / dims.h)
+    end)
+end, { complex = true })
+
+mp.register_script_message("cursor-centric-zoom", function (amount)
+    local command = (options.suppress_osd and "no-osd " or "") ..
+                    "add video-zoom " .. amount .. ";"
+
+    local x, y
+    local touch_positions = mp.get_property_native("touch-pos")
+    if next(touch_positions) then
+        for _, position in pairs(touch_positions) do
+            x = x + position.x
+            y = y + position.y
+        end
+        x = x / #touch_positions
+        y = y / #touch_positions
+    else
+        local mouse_pos = mp.get_property_native("mouse-pos")
+        x = mouse_pos.x
+        y = mouse_pos.y
+    end
+
+    local dims = mp.get_property_native("osd-dimensions")
+    local width = (dims.w - dims.ml - dims.mr) * 2^amount
+    local height = (dims.h - dims.mt - dims.mb) * 2^amount
+
+    local old_cursor_ml = dims.ml - x
+    local cursor_ml = old_cursor_ml * 2^amount
+    local ml = cursor_ml + x
+    -- video/out/aspect.c:src_dst_split_scaling() defines ml as:
+    -- ml = (osd-width - width) * (video-align-x + 1) / 2 + pan-x * width
+    -- So video-align-x is:
+    local align = 2 * (ml - mp.get_property_native("video-pan-x") * width)
+                  / (dims.w - width) - 1
+    command = command .. "no-osd set video-align-x " ..
+              math.min(1, math.max(align, -1)) .. ";"
+
+    local mt = (dims.mt - y) * 2^amount + y
+    align = 2 * (mt - mp.get_property_native("video-pan-y") * height)
+            / (dims.h - height) - 1
+    command = command .. "no-osd set video-align-y " ..
+              math.min(1, math.max(align, -1))
+
+    mp.command(command)
+end)

player/scripting.c

@@ -263,6 +263,7 @@ void mp_load_builtin_scripts(struct MPContext *mpctx)
     load_builtin_script(mpctx, 4, mpctx->opts->lua_load_auto_profiles,
                         "@auto_profiles.lua");
     load_builtin_script(mpctx, 5, mpctx->opts->lua_load_select, "@select.lua");
+    load_builtin_script(mpctx, 6, mpctx->opts->lua_load_positioning, "@positioning.lua");
 }
 
 bool mp_load_scripts(struct MPContext *mpctx)