command: add cursor-centric-zoom

DOCS/interface-changes/cursor-centric-zoom.txt

@@ -0,0 +1 @@
+add `cursor-centric-zoom` command

DOCS/man/input.rst

@@ -1527,6 +1527,11 @@ Remember to quote string arguments in input.conf (see `Flat command syntax`_).
     of window dragging. For example, on Windows only the left mouse button can
     begin window dragging, while X11 and Wayland allow other mouse buttons.
 
+``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.
+
 Undocumented commands: ``ao-reload`` (experimental/internal).
 
 List of events

DOCS/man/mpv.rst

@@ -354,7 +354,8 @@ Wheel left/right
     Seek forward/backward 10 seconds.
 
 Ctrl+Wheel up/down
-    Change video zoom.
+    Change video zoom and shift the OSD towards the position hovered by the
+    cursor.
 
 Context Menu
 -------------

etc/input.conf

@@ -65,9 +65,9 @@
 #ZOOMIN    add video-zoom   0.1         # zoom in
 #Alt+-     add video-zoom  -0.1         # zoom out
 #ZOOMOUT   add video-zoom  -0.1         # zoom out
-#Ctrl+WHEEL_UP   add video-zoom  0.1    # zoom in
-#Ctrl+WHEEL_DOWN add video-zoom -0.1    # zoom out
-#Alt+BS set video-zoom 0; set panscan 0; set video-pan-x 0; set video-pan-y 0 # reset zoom and pan settings
+#Ctrl+WHEEL_UP   cursor-centric-zoom  0.1 # zoom in
+#Ctrl+WHEEL_DOWN cursor-centric-zoom -0.1 # zoom out
+#Alt+BS set video-zoom 0; no-osd set panscan 0; no-osd set video-pan-x 0; no-osd set video-pan-y 0; no-osd set video-align-x 0; no-osd set video-align-y 0 # reset zoom and pan settings
 #PGUP add chapter 1                     # seek to the next chapter
 #PGDWN add chapter -1                   # seek to the previous chapter
 #Shift+PGUP seek 600                    # seek 10 minutes forward

player/command.c

@@ -6813,6 +6813,54 @@ static void cmd_flush_status_line(void *p)
     mp_msg_flush_status_line(mpctx->log, cmd->args[0].v.b);
 }
 
+static void cmd_cursor_centric_zoom(void *p)
+{
+    struct mp_cmd_ctx *cmd = p;
+    struct MPContext *mpctx = cmd->mpctx;
+
+    double zoom = cmd->args[0].v.d * cmd->cmd->scale;
+
+    int x = 0, y = 0;
+    int xs[MAX_TOUCH_POINTS], ys[MAX_TOUCH_POINTS], ids[MAX_TOUCH_POINTS];
+    int count = mp_input_get_touch_pos(mpctx->input, MAX_TOUCH_POINTS, xs, ys, ids);
+    if (count) {
+        for (int i = 0; i < count; i++) {
+            x += xs[i];
+            y += ys[i];
+        }
+        x /= count;
+        y /= count;
+    } else {
+        int hover;
+        mp_input_get_mouse_pos(mpctx->input, &x, &y, &hover);
+    }
+
+    struct mp_osd_res dims = osd_get_vo_res(mpctx->osd);
+    int width = (dims.w - dims.ml - dims.mr) * pow(2, zoom);
+    int height = (dims.h - dims.mt - dims.mb) * pow(2, zoom);
+
+    if (width > dims.w) {
+        int old_cursor_ml = dims.ml - x;
+        int cursor_ml = old_cursor_ml * pow(2, zoom);
+        int 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:
+        float align = 2.0 * (ml - mpctx->video_out->opts->pan_x * width) / (dims.w - width) - 1;
+        align = MPMIN(1, MPMAX(-1, align));
+        mp_property_do("video-align-x", M_PROPERTY_SET, &align, mpctx);
+    }
+
+    if (height > dims.h) {
+        int mt = (dims.mt - y) * pow(2, zoom) + y;
+        float align = 2.0 * (mt - mpctx->video_out->opts->pan_y * height) / (dims.h - height) - 1;
+        align = MPMIN(1, MPMAX(-1, align));
+        mp_property_do("video-align-y", M_PROPERTY_SET, &align, mpctx);
+    }
+
+    change_property_cmd(cmd, "video-zoom", M_PROPERTY_SWITCH, &zoom);
+}
+
 /* This array defines all known commands.
  * The first field the command name used in libmpv and input.conf.
  * The second field is the handler function (see mp_cmd_def.handler and
@@ -7291,6 +7339,11 @@ const struct mp_cmd_def mp_cmds[] = {
 
     { "flush-status-line", cmd_flush_status_line, { {"clear", OPT_BOOL(v.b)} } },
 
+    { "cursor-centric-zoom", cmd_cursor_centric_zoom, {
+        {"zoom", OPT_DOUBLE(v.d)}, },
+        .allow_auto_repeat = true,
+        .scalable = true,
+    },
     {0}
 };