xwayland: Update the global screen scale

Recompute and update the global screen scale based on the different
outputs the root window is placed on.

For backward compatibility, this functionality is however disabled by
default and can be enabled using a new command line option "-hidpi".

That option has no effect if Xwayland is running rootless.

Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
Reviewed-By: Kenny Levinsen <kl@kl.wtf>
Acked-by: Peter Hutterer <peter.hutterer@who-t.net>
Part-of: <https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/1197>

hw/xwayland/man/Xwayland.man

@@ -82,6 +82,11 @@ and fallback to GL ES if GL version is less than 2.1.
 
 This option is not compatible with \fI-shm\fP option.
 .TP 8
+.B \-hidpi
+Adjust to the scale of the outputs when running rootful in windowing mode.
+
+This option is not compatible with rootless mode (\fI-rootless\fP).
+.TP 8
 .B \-host-grab
 Disable host keyboard shorcuts and confine the pointer when running rootful.
 

hw/xwayland/meson.build

@@ -174,6 +174,7 @@ xwayland_vars = [
     'have_decorate=' + have_libdecor.to_string(),
     'have_enable_ei_portal=' + build_ei_portal.to_string(),
     'have_byteswappedclients=true',
+    'have_hidpi=true',
 ]
 
 pkgconfig = import('pkgconfig')

hw/xwayland/xwayland-screen.c

@@ -768,6 +768,35 @@ xwl_screen_lost_focus(struct xwl_screen *xwl_screen)
     }
 }
 
+Bool
+xwl_screen_update_global_surface_scale(struct xwl_screen *xwl_screen)
+{
+    ScreenPtr screen = xwl_screen->screen;
+    struct xwl_window *xwl_window;
+    int32_t old_scale;
+
+    if (xwl_screen->rootless)
+        return FALSE;
+
+    if (xwl_screen->fullscreen)
+        return FALSE;
+
+    if (!xwl_screen->hidpi)
+        return FALSE;
+
+    if (screen->root == NullWindow)
+        return FALSE;
+
+    xwl_window = xwl_window_get(screen->root);
+    if (!xwl_window)
+        return FALSE;
+
+    old_scale = xwl_screen->global_surface_scale;
+    xwl_screen->global_surface_scale = xwl_window_get_max_output_scale(xwl_window);
+
+    return (xwl_screen->global_surface_scale != old_scale);
+}
+
 Bool
 xwl_screen_init(ScreenPtr pScreen, int argc, char **argv)
 {
@@ -881,6 +910,9 @@ xwl_screen_init(ScreenPtr pScreen, int argc, char **argv)
         else if (strcmp(argv[i], "-nokeymap") == 0) {
             xwl_screen->nokeymap = 1;
         }
+        else if (strcmp(argv[i], "-hidpi") == 0) {
+            xwl_screen->hidpi = 1;
+        }
     }
 
     if (!xwl_screen->rootless) {

hw/xwayland/xwayland-screen.h

@@ -66,6 +66,7 @@ struct xwl_screen {
     int decorate;
     int enable_ei_portal;
     int nokeymap;
+    int hidpi;
 
     CreateScreenResourcesProcPtr CreateScreenResources;
     CloseScreenProcPtr CloseScreen;
@@ -170,5 +171,6 @@ void xwl_surface_damage(struct xwl_screen *xwl_screen,
                         int32_t x, int32_t y, int32_t width, int32_t height);
 int xwl_screen_get_next_output_serial(struct xwl_screen * xwl_screen);
 void xwl_screen_lost_focus(struct xwl_screen *xwl_screen);
+Bool xwl_screen_update_global_surface_scale(struct xwl_screen *xwl_screen);
 
 #endif /* XWAYLAND_SCREEN_H */

hw/xwayland/xwayland-window.c

@@ -671,10 +671,10 @@ xwl_window_maybe_resize(struct xwl_window *xwl_window, double width, double heig
     xwl_screen->height = height;
 
     xwl_output = xwl_screen_get_fixed_or_first_output(xwl_screen);
-    if (!xwl_randr_add_modes_fixed(xwl_output, round(width), round(height)))
+    if (!xwl_randr_add_modes_fixed(xwl_output, round(width / scale), round(height / scale)))
         return;
 
-    mode = xwl_output_find_mode(xwl_output,  round(width), round(height));
+    mode = xwl_output_find_mode(xwl_output, round(width / scale), round(height / scale));
     xwl_output_set_mode_fixed(xwl_output, mode);
 
     xwl_window_attach_buffer(xwl_window);
@@ -797,7 +797,39 @@ static const struct xdg_surface_listener xdg_surface_listener = {
 static void
 xwl_window_update_surface_scale(struct xwl_window *xwl_window)
 {
+    struct xwl_screen *xwl_screen = xwl_window->xwl_screen;
+    int previous_scale, new_scale;
+    double new_width, new_height;
+
+    previous_scale = xwl_screen->global_surface_scale;
+    assert(previous_scale != 0);
     xwl_window->surface_scale = xwl_window_get_max_output_scale(xwl_window);
+
+    if (xwl_screen_update_global_surface_scale(xwl_screen)) {
+        new_scale = xwl_screen->global_surface_scale;
+
+        DebugF("XWAYLAND: Global scale is now %i (was %i)\n",
+               new_scale, previous_scale);
+
+        new_width = xwl_screen->width / previous_scale * new_scale;
+        new_height = xwl_screen->height / previous_scale * new_scale;
+
+        wl_surface_set_buffer_scale(xwl_window->surface, xwl_screen->global_surface_scale);
+        /* Reflect the scale factor using XRandR transform */
+        xwl_output_set_xscale(xwl_screen->fixed_output, new_scale);
+        xwl_window_maybe_resize(xwl_window, new_width, new_height);
+#ifdef XWL_HAS_LIBDECOR
+        if (xwl_window->libdecor_frame) {
+            xwl_window_libdecor_set_size_limits(xwl_window);
+            xwl_window_update_libdecor_size(xwl_window,
+                                            NULL,
+                                            round(new_width / new_scale),
+                                            round(new_height / new_scale));
+        }
+        else
+#endif
+            wl_surface_commit(xwl_window->surface);
+    }
 }
 
 static void

hw/xwayland/xwayland.c

@@ -97,6 +97,7 @@ ddxUseMsg(void)
     ErrorF("-rootless              run rootless, requires wm support\n");
     ErrorF("-fullscreen            run fullscreen when rootful\n");
     ErrorF("-geometry WxH          set Xwayland window size when rootful\n");
+    ErrorF("-hidpi                 adjust to output scale when rootful\n");
     ErrorF("-host-grab             disable host keyboard shortcuts when rootful\n");
     ErrorF("-nokeymap              ignore keymap from the Wayland compositor\n");
     ErrorF("-output                specify which output to use for fullscreen when rootful\n");
@@ -269,6 +270,9 @@ ddxProcessArgument(int argc, char *argv[], int i)
     else if (strcmp(argv[i], "-nokeymap") == 0) {
         return 1;
     }
+    else if (strcmp(argv[i], "-hidpi") == 0) {
+        return 1;
+    }
 
     return 0;
 }