command: add property returning hidpi scale

DOCS/man/input.rst

@@ -2073,6 +2073,12 @@ Property list
 ``vsync-jitter``
     Estimated deviation factor of the vsync duration.
 
+``display-hidpi-scale``
+    The HiDPI scale factor as reported by the windowing backend. If no VO is
+    active, or if the VO does not report a value, this property is unavailable.
+    It may be saner to report an absolute DPI, however, this is the way HiDPI
+    support is implemented on most OS APIs. See also ``--hidpi-window-scale``.
+
 ``video-aspect`` (RW)
     Deprecated. This is tied to ``--video-aspect-override``, but always
     reports the current video aspect if video is active.

player/command.c

@@ -2325,6 +2325,17 @@ static int mp_property_vsync_jitter(void *ctx, struct m_property *prop,
     return m_property_double_ro(action, arg, stddev);
 }
 
+static int mp_property_hidpi_scale(void *ctx, struct m_property *prop,
+                                   int action, void *arg)
+{
+    MPContext *mpctx = ctx;
+    struct vo *vo = mpctx->video_out;
+    double scale = 0;
+    if (!vo || vo_control(vo, VOCTRL_GET_HIDPI_SCALE, &scale) < 1 || scale <= 0)
+        return M_PROPERTY_UNAVAILABLE;
+    return m_property_double_ro(action, arg, scale);
+}
+
 static int mp_property_display_names(void *ctx, struct m_property *prop,
                                      int action, void *arg)
 {
@@ -3398,6 +3409,7 @@ static const struct m_property mp_properties_base[] = {
     {"display-fps", mp_property_display_fps},
     {"estimated-display-fps", mp_property_estimated_display_fps},
     {"vsync-jitter", mp_property_vsync_jitter},
+    {"display-hidpi-scale", mp_property_hidpi_scale},
 
     {"working-directory", mp_property_cwd},
 

video/out/vo.h

@@ -116,6 +116,7 @@ enum mp_voctrl {
     VOCTRL_GET_ICC_PROFILE,             // bstr*
     VOCTRL_GET_AMBIENT_LUX,             // int*
     VOCTRL_GET_DISPLAY_FPS,             // double*
+    VOCTRL_GET_HIDPI_SCALE,             // double*
 
     VOCTRL_GET_PREF_DEINT,              // int*