scratchpad: set initial size

This matches i3's behavior of setting scratchpad containers to 50% of
the workspace's width and 75% of the workspace's height, bound by the
minimum and maximum floating width/height.

include/sway/tree/container.h

@@ -217,6 +217,8 @@ void floating_calculate_constraints(int *min_width, int *max_width,
 
 void container_floating_resize_and_center(struct sway_container *con);
 
+void container_floating_set_default_size(struct sway_container *con);
+
 void container_set_floating(struct sway_container *container, bool enable);
 
 void container_set_geometry_from_content(struct sway_container *con);

sway/tree/container.c

@@ -712,19 +712,28 @@ void container_floating_resize_and_center(struct sway_container *con) {
 	}
 }
 
-static void container_floating_set_default_size(struct sway_container *con) {
+void container_floating_set_default_size(struct sway_container *con) {
 	if (!sway_assert(con->workspace, "Expected a container on a workspace")) {
 		return;
 	}
+
 	int min_width, max_width, min_height, max_height;
 	floating_calculate_constraints(&min_width, &max_width,
 			&min_height, &max_height);
 	struct wlr_box *box = calloc(1, sizeof(struct wlr_box));
 	workspace_get_box(con->workspace, box);
+
+	double width = fmax(min_width, fmin(box->width * 0.5, max_width));
+	double height = fmax(min_height, fmin(box->height * 0.75, max_height));
 	if (!con->view) {
-		con->width = fmax(min_width, fmin(box->width * 0.5, max_width));
+		con->width = width;
-		con->height = fmax(min_height, fmin(box->height * 0.75, max_height));
+		con->height = height;
+	} else {
+		con->content_width = width;
+		con->content_height = height;
+		container_set_geometry_from_content(con);
 	}
+
 	free(box);
 }
 

sway/tree/root.c

@@ -62,6 +62,8 @@ void root_scratchpad_add_container(struct sway_container *con) {
 	struct sway_container *parent = con->parent;
 	struct sway_workspace *workspace = con->workspace;
 	container_set_floating(con, true);
+	container_floating_set_default_size(con);
+	container_floating_move_to_center(con);
 	container_detach(con);
 	con->scratchpad = true;
 	list_add(root->scratchpad, con);