wayland: set geometry directly to output resolution for fullscreen

Unfortunately due to the way fractional scaling on wayland works, it
can lead to rounding errors when calculating the physical size of the
buffer. It's convoluted but essentially the compositor will communicate
the logical size back to us. Depending on the fractional scale factor,
the communicated size can be truncated in a significant enough way that
causes final calculated size to be off by a maximum of two (truncation
at both steps).

In general, there's nothing we can really do about this but for
specifically fullscreen there's an easy enough workaround. Just set the
size to be the same as the output. Since we might not have rendered the
surface yet (and thus not have an easily accessible wl->current_output),
it's easier to just loop through the output list until we have a match.

Fixes #17415.

Author: Dudemanguy

video/out/wayland_common.c

@@ -310,6 +310,7 @@ static void add_feedback(struct vo_wayland_feedback_pool *fback_pool,
                          struct wp_presentation_feedback *fback);
 static void apply_keepaspect(struct vo_wayland_state *wl, int *width, int *height);
 static void get_compositor_preferred_description(struct vo_wayland_state *wl);
+static void get_fullscreen_dims(struct vo_wayland_state *wl);
 static void get_shape_device(struct vo_wayland_state *wl, struct vo_wayland_seat *s);
 static void guess_focus(struct vo_wayland_state *wl);
 static void handle_key_input(struct vo_wayland_seat *s, uint32_t key, uint32_t state, bool no_emit);
@@ -1921,6 +1922,8 @@ static void handle_toplevel_config(void *data, struct xdg_toplevel *toplevel,
     wl->geometry.x1 = handle_round(wl->scaling, width);
     wl->geometry.y1 = handle_round(wl->scaling, height);
 
+    get_fullscreen_dims(wl);
+
     if (mp_rect_equals(&old_geometry, &wl->geometry))
         return;
 
@@ -3128,6 +3131,26 @@ static void get_compositor_preferred_description(struct vo_wayland_state *wl)
 #endif
 }
 
+static void get_fullscreen_dims(struct vo_wayland_state *wl)
+{
+    if (!wl->opts->fullscreen || !wl->fractional_scale_manager)
+        return;
+
+    // Fractional scaling can have pixel rounding errors (max of 2).
+    // For fullscreen, loop through output geometry and find a valid match.
+    int width = mp_rect_w(wl->geometry);
+    int height = mp_rect_h(wl->geometry);
+    struct vo_wayland_output *output;
+    wl_list_for_each(output, &wl->output_list, link) {
+        if (abs(mp_rect_w(output->geometry) - width <= 2) && abs(mp_rect_h(output->geometry) - height) <= 2) {
+            wl->geometry.x1 = mp_rect_w(output->geometry);
+            wl->geometry.y1 = mp_rect_h(output->geometry);
+            return;
+        }
+    }
+    return;
+}
+
 static void get_shape_device(struct vo_wayland_state *wl, struct vo_wayland_seat *s)
 {
     if (!s->cursor_shape_device && wl->cursor_shape_manager) {