x11: pseudo HiDPI scaling

Scale the window by the assumed DPI scaling factor, using 96 DPI as
base. For example, a screen that reports 192 DPI is assumed to have a
DPI scale factor 2. The window will then be created with twice the size.

For robustness reasons, we accept only integer DPI scales between 1 and
9. We also error out if the X and Y scales are very different, as this
most likely indicates a multiscreen system with botched size reporting.

I'm not sure if reading the X server's DPI is such a good idea - maybe
the Xrdb "Xft.dpi" value should be used instead. The current method
follows what xdpyinfo does.

This can be disabled with --hidpi-window-scale=no.

1 files changed, 17 insertions, 4 deletions

diff --git a/video/out/win_state.c b/video/out/win_state.c
index 29eaa1b663..3546daadec 100644
--- a/video/out/win_state.c
+++ b/video/out/win_state.c
@@ -67,13 +67,17 @@ static void apply_autofit(int *w, int *h, int scr_w, int scr_h,
 // Compute the "suggested" window size and position and return it in *out_geo.
 // screen is the bounding box of the current screen within the virtual desktop.
 // Does not change *vo.
+//  screen: position of the screen on virtual desktop on which the window
+//          should be placed
+//  dpi_scale: the DPI multiplier to get from virtual to real coordinates
+//             (>1 for "hidpi")
 // Use vo_apply_window_geometry() to copy the result into the vo.
 // NOTE: currently, all windowing backends do their own handling of window
 //       geometry additional to this code. This is to deal with initial window
 //       placement, fullscreen handling, avoiding resize on reconfig() with no
 //       size change, multi-monitor stuff, and possibly more.
-void vo_calc_window_geometry(struct vo *vo, const struct mp_rect *screen,
-                             struct vo_win_geometry *out_geo)
+void vo_calc_window_geometry2(struct vo *vo, const struct mp_rect *screen,
+                              double dpi_scale, struct vo_win_geometry *out_geo)
 {
     struct mp_vo_opts *opts = vo->opts;
 
@@ -86,12 +90,15 @@ void vo_calc_window_geometry(struct vo *vo, const struct mp_rect *screen,
     if (vo->params)
         params = *vo->params;
 
+    if (!opts->hidpi_window_scale)
+        dpi_scale = 1;
+
     int d_w, d_h;
     mp_image_params_get_dsize(&params, &d_w, &d_h);
     if ((vo->driver->caps & VO_CAP_ROTATE90) && params.rotate % 180 == 90)
         MPSWAP(int, d_w, d_h);
-    d_w = MPCLAMP(d_w * opts->window_scale, 1, 16000);
-    d_h = MPCLAMP(d_h * opts->window_scale, 1, 16000);
+    d_w = MPCLAMP(d_w * opts->window_scale * dpi_scale, 1, 16000);
+    d_h = MPCLAMP(d_h * opts->window_scale * dpi_scale, 1, 16000);
 
     int scr_w = screen->x1 - screen->x0;
     int scr_h = screen->y1 - screen->y0;
@@ -118,6 +125,12 @@ void vo_calc_window_geometry(struct vo *vo, const struct mp_rect *screen,
         out_geo->flags |= VO_WIN_FORCE_POS;
 }
 
+void vo_calc_window_geometry(struct vo *vo, const struct mp_rect *screen,
+                             struct vo_win_geometry *out_geo)
+{
+    vo_calc_window_geometry2(vo, screen, 1.0, out_geo);
+}
+
 // Copy the parameters in *geo to the vo fields.
 // (Doesn't do anything else - windowing backends should trigger VO_EVENT_RESIZE
 //  to ensure that the VO reinitializes rendering properly.)