view: constrain window size to that of usable area

...on first map (when application is started).

Fixes #1399

include/view.h

@@ -407,6 +407,7 @@ void view_center(struct view *view, const struct wlr_box *ref);
  * @view: view to be placed
  */
 void view_place_initial(struct view *view);
+void view_constrain_size_to_that_of_usable_area(struct view *view);
 
 void view_restore_to(struct view *view, struct wlr_box geometry);
 void view_set_untiled(struct view *view);

src/view.c

@@ -731,6 +731,25 @@ view_place_initial(struct view *view)
 	view_center(view, NULL);
 }
 
+void
+view_constrain_size_to_that_of_usable_area(struct view *view)
+{
+	if (!view || !view->output) {
+		return;
+	}
+	struct wlr_box *usable_area = &view->output->usable_area;
+	struct border margin = ssd_get_margin(view->ssd);
+	struct wlr_box box = {
+		.x = view->pending.x,
+		.y = view->pending.y,
+		.width = MIN(usable_area->width - margin.left - margin.right,
+			view->pending.width),
+		.height = MIN(usable_area->height - margin.top - margin.bottom,
+			view->pending.height),
+	};
+	view_move_resize(view, box);
+}
+
 static void
 view_apply_natural_geometry(struct view *view)
 {

src/xdg.c

@@ -420,6 +420,8 @@ position_xdg_toplevel_view(struct view *view)
 	struct wlr_xdg_toplevel *parent_xdg_toplevel =
 		xdg_toplevel_from_view(view)->parent;
 
+	view_constrain_size_to_that_of_usable_area(view);
+
 	if (parent_xdg_toplevel) {
 		/* Child views are center-aligned relative to their parents */
 		struct view *parent = lookup_view_by_xdg_toplevel(

src/xwayland.c

@@ -505,6 +505,8 @@ set_initial_position(struct view *view,
 			XCB_ICCCM_SIZE_HINT_US_POSITION |
 			XCB_ICCCM_SIZE_HINT_P_POSITION));
 
+	view_constrain_size_to_that_of_usable_area(view);
+
 	if (has_position) {
 		/*
 		 * Make sure a floating view is onscreen. For a