1.6 to 1.7 migration

A few changes to basic project structures were made with the PlayN 1.7 release. This document describes those changes and how to update your PlayN project to accommodate them.


Previously your game implemented the Game interface and provided implementations of a few methods:

public class MyGame implements Game {
  public void init () {}
  public void update (float delta) {}
  public void paint (float alpha) {}
  public int updateRate () { return N; }

Now your game should extend Game.Default, and pass its update rate into the Game.Default constructor:

public class MyGame extends Game.Default {
  public MyGame () {
  public void init () {}
  public void update (int delta) {}
  public void paint (float alpha) {}

Note also that update takes int delta instead of float delta. The delta value is a number of milliseconds and was never non-integral.

This release also improves the smoothness of update and paint calls. As long as you are properly using alpha to interpolate between simulation updates, you should simply see your game run smoother.

If you wish to implement your own custom approach to update and paint you can implement Game directly instead of using Game.Default. In that case, you implement the tick method (instead of update and paint) and decide how to handle simulation updates and paints yourself:

public class MyGame implements Game {
  public void init () {}
  public void tick (int elapsed) {}

You can look at the source code for Game.Default to see how it handles simulation and painting updates, and tweak or replace the default algorithm.

Upstream JBox2D now supports GWT

Previously, PlayN maintained a fork of the JBox2D code base with small tweaks to make it work with GWT (so that it would work with the HTML backend). Those tweaks have been merged upstream, and now it is possible to use the latest release of JBox2D ( directly with PlayN.

PlayN still provides a playn-jbox2d artifact, which provides a DebugDraw2D implementation that allows one to render debug information for JBox2D games, but that artifact no longer provides JBox2D itself. If your game does not use the HTML backend, you don’t need to make any changes to your project configuration. If your game does use JBox2D and the HTML backend, there are two changes that are needed.

  1. Add a dependency to the JBox2D source artifact to your html/pom.xml:

Note that the PlayN project POM defines jbox2d.version, so you don’t need to define that in your top-level POM.

  1. Change GwtBox2D to JBox2D in your GWT module file:
-  <inherits name="org.jbox2d.GwtBox2D" />
+  <inherits name="org.jbox2d.JBox2D" />

Using the latest version of JBox2D will require that you update your game to use the latest JBox2D APIs. You can view the Box2D manual for information on the latest API: http://box2d.org/manual.pdf

SurfaceLayer replaced with SurfaceImage + ImageLayer

A Surface provides a hardware accelerated bitmap into which a game can render, and which can then be displayed in the scene graph. Previously surfaces were tightly bound a special layer, SurfaceLayer, which was the only way to create and render to such a bitmap.

Now surfaces have been decoupled from layers and are just another kind of Image. CanvasImage provides a non-hardware accelerated bitmap into which a game can render, and now SurfaceImage provides a hardware accelerated bitmap into which a game can render. A SurfaceImage can then be placed into one or more ImageLayer instances to be included in a scene graph, or a SurfaceImage can be drawn via the immediate-mode rendering mechanism provided by ImmediateLayer.

If you had code like:

SurfaceLayer layer = graphics().createSurfaceLayer(width, height);
graphics().rootLayer().addAt(layer, 10, 10);

You can change that code to:

SurfaceImage image = graphics().createSurface(width, height);
ImageLayer layer = graphics().createImageLayer(image);
graphics().rootLayer().addAt(layer, 10, 10);

Everything that was possible with SurfaceLayer is still possible with SurfaceImage and many other previously impossible things are now possible. That said, there are some limitations in the current implementation, some of which will be remedied in the future and some of which are simply limitations due to the nature of surface images being GPU-managed bitmaps:

I would have preferred to restructure the class hierarchy of Image, CanvasImage and SurfaceImage to make it impossible to call methods on SurfaceImage which can never be made to work, but it would have required Image to be changed to a new type, which would have been a massive disruption to the codebase of every PlayN game in existence. So I decided that this slightly sloppier API which admits impossible requests was a better approach.