Center surface inside container when it's too small

The goal here is to center fullscreen views when they are both too small
for the output and refuse to resize to the output's dimensions. It has
the side effect of also centering the view when it's too small for its
container.

Example clients that have this behaviour are emersion's hello-wayland
and weston.

It works by introducing surface_{x,y,width,height} properties to the
container struct. The x and y represent layout-local coordinates where
the surface will be rendered. The width and height are only used to
track the surface's previous dimensions so we can detect when the client
has resized it and recenter and apply damage accordingly.

The new surface properties are calculated when a transaction is applied,
as well as when a view resizes itself unexpectedly. The latter is done
in view_update_size. This function was previously restricted to views
which are floating, but can now be called for any views.

For views which refuse to resize *smaller* than a particular size, such
as gnome-calculator, the surface is still anchored to the top left as
per the current behaviour.

include/sway/tree/container.h

@@ -88,9 +88,16 @@ struct sway_container {
 	double saved_x, saved_y;
 	double saved_width, saved_height;
 
+	// These are in layout coordinates.
 	double content_x, content_y;
 	int content_width, content_height;
 
+	// In most cases this is the same as the content x and y, but if the view
+	// refuses to resize to the content dimensions then it can be smaller.
+	// These are in layout coordinates.
+	double surface_x, surface_y;
+	double surface_width, surface_height;
+
 	enum sway_fullscreen_mode fullscreen_mode;
 
 	enum sway_container_border border;

sway/desktop/render.c

@@ -204,9 +204,9 @@ static void render_view_toplevels(struct sway_view *view,
 		.alpha = alpha,
 	};
 	// Render all toplevels without descending into popups
-	double ox = view->container->current.content_x -
+	double ox = view->container->surface_x -
 		output->wlr_output->lx - view->geometry.x;
-	double oy = view->container->current.content_y -
+	double oy = view->container->surface_y -
 		output->wlr_output->ly - view->geometry.y;
 	output_surface_for_each_surface(output, view->surface, ox, oy,
 			render_surface_iterator, &data);
@@ -240,9 +240,9 @@ static void render_saved_view(struct sway_view *view,
 		return;
 	}
 	struct wlr_box box = {
-		.x = view->container->current.content_x - output->wlr_output->lx -
+		.x = view->container->surface_x - output->wlr_output->lx -
 			view->saved_geometry.x,
-		.y = view->container->current.content_y - output->wlr_output->ly -
+		.y = view->container->surface_y - output->wlr_output->ly -
 			view->saved_geometry.y,
 		.width = view->saved_buffer_width,
 		.height = view->saved_buffer_height,
@@ -1004,7 +1004,6 @@ void output_render(struct sway_output *output, struct timespec *when,
 			wlr_renderer_clear(renderer, clear_color);
 		}
 
-		// TODO: handle views smaller than the output
 		if (fullscreen_con->view) {
 			if (fullscreen_con->view->saved_buffer) {
 				render_saved_view(fullscreen_con->view, output, damage, 1.0f);

sway/desktop/transaction.c

@@ -249,6 +249,26 @@ static void apply_container_state(struct sway_container *container,
 		desktop_damage_box(&box);
 	}
 
+	// If the view hasn't responded to the configure, center it within
+	// the container. This is important for fullscreen views which
+	// refuse to resize to the size of the output.
+	if (view && view->surface) {
+		if (view->surface->current.width < container->width) {
+			container->surface_x = container->content_x +
+				(container->content_width - view->surface->current.width) / 2;
+		} else {
+			container->surface_x = container->content_x;
+		}
+		if (view->surface->current.height < container->height) {
+			container->surface_y = container->content_y +
+				(container->content_height - view->surface->current.height) / 2;
+		} else {
+			container->surface_y = container->content_y;
+		}
+		container->surface_width = view->surface->current.width;
+		container->surface_height = view->surface->current.height;
+	}
+
 	if (!container->node.destroying) {
 		container_discover_outputs(container);
 	}

sway/desktop/xdg_shell.c

@@ -291,10 +291,9 @@ static void handle_commit(struct wl_listener *listener, void *data) {
 		wlr_xdg_surface_get_geometry(xdg_surface, &new_geo);
 		struct sway_container *con = view->container;
 
-		if ((new_geo.width != con->content_width ||
-					new_geo.height != con->content_height) &&
-				container_is_floating(con)) {
-			// A floating view has unexpectedly sent a new size
+		if ((new_geo.width != con->surface_width ||
+					new_geo.height != con->surface_height)) {
+			// The view has unexpectedly sent a new size
 			desktop_damage_view(view);
 			view_update_size(view, new_geo.width, new_geo.height);
 			memcpy(&view->geometry, &new_geo, sizeof(struct wlr_box));

sway/desktop/xdg_shell_v6.c

@@ -284,10 +284,9 @@ static void handle_commit(struct wl_listener *listener, void *data) {
 		wlr_xdg_surface_v6_get_geometry(xdg_surface_v6, &new_geo);
 		struct sway_container *con = view->container;
 
-		if ((new_geo.width != con->content_width ||
-					new_geo.height != con->content_height) &&
-				container_is_floating(con)) {
-			// A floating view has unexpectedly sent a new size
+		if ((new_geo.width != con->surface_width ||
+					new_geo.height != con->surface_height)) {
+			// The view has unexpectedly sent a new size
 			desktop_damage_view(view);
 			view_update_size(view, new_geo.width, new_geo.height);
 			memcpy(&view->geometry, &new_geo, sizeof(struct wlr_box));

sway/desktop/xwayland.c

@@ -333,10 +333,9 @@ static void handle_commit(struct wl_listener *listener, void *data) {
 		get_geometry(view, &new_geo);
 		struct sway_container *con = view->container;
 
-		if ((new_geo.width != con->content_width ||
-					new_geo.height != con->content_height) &&
-				container_is_floating(con)) {
-			// A floating view has unexpectedly sent a new size
+		if ((new_geo.width != con->surface_width ||
+					new_geo.height != con->surface_height)) {
+			// The view has unexpectedly sent a new size
 			// eg. The Firefox "Save As" dialog when downloading a file
 			desktop_damage_view(view);
 			view_update_size(view, new_geo.width, new_geo.height);

sway/tree/container.c

@@ -169,8 +169,8 @@ static struct sway_container *surface_at_view(struct sway_container *con, double
 		return NULL;
 	}
 	struct sway_view *view = con->view;
-	double view_sx = lx - con->content_x + view->geometry.x;
-	double view_sy = ly - con->content_y + view->geometry.y;
+	double view_sx = lx - con->surface_x + view->geometry.x;
+	double view_sy = ly - con->surface_y + view->geometry.y;
 
 	double _sx, _sy;
 	struct wlr_surface *_surface = NULL;

sway/tree/view.c

@@ -673,15 +673,22 @@ void view_unmap(struct sway_view *view) {
 }
 
 void view_update_size(struct sway_view *view, int width, int height) {
-	if (!sway_assert(container_is_floating(view->container),
-				"Expected a floating container")) {
-		return;
+	struct sway_container *con = view->container;
+
+	if (container_is_floating(con)) {
+		con->content_width = width;
+		con->content_height = height;
+		con->current.content_width = width;
+		con->current.content_height = height;
+		container_set_geometry_from_content(con);
+	} else {
+		con->surface_x = con->content_x + (con->content_width - width) / 2;
+		con->surface_y = con->content_y + (con->content_height - height) / 2;
+		con->surface_x = fmax(con->surface_x, con->content_x);
+		con->surface_y = fmax(con->surface_y, con->content_y);
 	}
-	view->container->content_width = width;
-	view->container->content_height = height;
-	view->container->current.content_width = width;
-	view->container->current.content_height = height;
-	container_set_geometry_from_content(view->container);
+	con->surface_width = width;
+	con->surface_width = height;
 }
 
 static const struct sway_view_child_impl subsurface_impl;