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25. April 2016

 

One of the major advantages to working in 3D is once you have your character modeled and rigged, creating new animations is simply a matter of defining a series of poses on a timeline.  Animations are generally defined by moving a series of bones controlling your mesh, which in turn are powered by a system called inverse kinematics.  IK is basically a fancy way of saying “move an end bone and the computer will calculate how all the other bones in the chain will respond” enabling you to animate by positioning the foot forimage example and the ankle, knee and hip will rotate appropriately.  It’s a pretty powerful way to perform animation and every single major 3D application implements IK (and FK – forward kinematics).

 

In the land of 2D art, the process is often quite different.  Generally the approach here is to generate a sprite sheet, which is a sequence of slightly altered versions of the same character, which played in sequence results in an animation.  If you ever done a flipbook animation at the top corner of any of your textbooks, you already have the process of traditional 2D animation down.  There are other techniques such as onion skinning and rotoscoping to aid in the animation process, but it still remains time intensive.  If only there was some way to take the 3D worlds bone based animations and apply them to generating 2D art?  Well, there is... Spine.

 

Today we are going to look inside Spine, look at the art generation process, how to make sprite graphics that are animation ready, define an animation, then perhaps most importantly, play that animation back in our game engine of choice.  Since Spine itself is built over top of the LibGDX library (by one of the frameworks founders to boot), therefore I suppose a LibGDX example makes the most sense.  If you are bored, the story of how Spine came to be is an interesting read.

 

Full disclosure, I requested a review license in order to get hands on time with Spine.  Additionally some of the assets I am using in this demonstration are part of asset packs available for purchase and aren’t my creation.  Spine is commercial software, ranging in price from $70 for the essentials version, $300 for professional and $2200 for enterprise (which is tied to your companies revenue).  There is a free trial available and capable of doing everything we are about to do below except export and run in code.  Without further ado, let’s jump in.  As is often the case on GameFromScratch, if you prefer a video version one is available here as well as embedded below.

 

Meet Spine

Here is the main Spine interface:

image

 

It’s actually an exercise in simplicity which I appreciate.  It also supports UI scaling, so works well on high DPI displays, something far too many applications suck at, so I also appreciate that.  The left hand viewport is where the magic happens, this is where you compose your characters and animations, while on the right hand side you’ve got your project hierarchy a scene graph of sorts.  The primary UI is across the bottom of the screen.  You can easily pan and zoom around the display using a combination or RMB and Ctrl + RMB.  There is some additional complexity hidden away behind this menu:

image

 

But most of the time, what you see is actually all that you need.  It’s a very clean and simple UI.  Notice in the top left corner it says SETUP.  This is because you are currently in Setup mode.  Once our Sprite has been assembled and our bones have been arranged ( more on this in a moment ), we can then switch in to animation mode by clicking SETUP.

image

In animation mode, its all about posing our character.  Notice SETUP changes to ANIMATE and our interface changes slightly.  Now we have a timeline across the bottom of the screen.  We will get back to that in a moment.

 

Creating Spine Ready Sprites

Creating a sprite that is ready to be animated in Spine is pretty close to traditional sprite based animation with two major exceptions.  First, you cut your image up into several different pieces.  You can draw your sprite as a single image if you wish, but once you are done you need to cut it into several different animatable pieces.  Consider the sprite from the above screenshots:

image

This looks like a single drawn sprite, but it’s actually made up for several pieces arranged together.  If you look in the images section of the hierarchy, you can see it’s actually composed of several different images:

image

 

Again, you can draw your sprite how you normally would, but each animatable piece will need to be cut up to proceed in Spine.  This leads to our second requirement...  you also need to draw parts of the images that are normally obscured.  Again, using this example, even if the upper arm isn’t full shown due to being obscured by the body you still need to draw the entire arm, as the visibility can change as the sprite moves, for example:

imageimage

 

So when drawing the pieces of your sprite, you have to think about the depth as well.  Here for example are all the pieces that go together to make this character:

image

 

Rigging Your Character

Next up comes perhaps the most time intensive portion of working with Spine, rigging you character.  You can think of this as arranging all the various images together to create your character, while defining the underlying armature (fancy word for skeleton).  We will do a very simple skeleton, just to demonstrate the process.  You will notice in the tree view that there is a root node under our skeleton:

image

 

This is the very base of the skeleton and all bones are parented to it ultimately.  From here we need to create a root bone, it’s very common to start from the hips, which is what we will do.  Using the create tool, we will quickly create a simple leg skeleton:

image

Click once to set the start of the skeleton, then move the mouse and click again to set the first bone.  Now move down slightly and set another bone, like so:

image

In the hierarchy I rename the bones to values that make sense.

image

Now that we have bones, let’s attach some images to each.  From the images section you can simply drag the appropriate image onto the bone, like so:

image

You will be prompted if you want to go ahead with it:

image

 

The image is now parented to that bone.  By selecting the image you can now transform, rotate and resize it so it best matches the underlying bone:

image

You can also modifying the bone length by hovering over the tip, like so:

GIF

 

Now repeat for the lower bone, like so:

image

 

You end up with a hierarchy like:

image

 

Extremely simple, but the character is rigged, well, the leg is anyways.

 

Creating an Animation

 

Now that we have a very simple animatable character, let’s now switch over to ANIMATE mode.  In the tree view, you should see a section called Animations.  There may be a default one there, otherwise create one using the New Animation button that appears when animation is selected:

image

image

 

Keyframed animation is pretty simple in concept.  You will notice at the bottom of the screen there is now a Dopesheet view:

image

 

Your animation is composed of a set of “key” frames.  That is, you post your character and take a snapshot of the location/rotation/scale of a given bone, then advance the timeline to a different value and repeat the process.  The computer then interpolates between keyframes to create a smooth animation.  You can turn “autokey” on, so that any changes you make in the editing window automatically set a key.  Otherwise you can manually create the key by clicking the green key to the right of each transform:

image

 

Set a key for the default rotate, translate and scale values, or use Autokey.  Next advance the timeline to say 5, like so:

image

 

Next using rotations, manipulate each bone, like so:

gif2

 

Advance the timeline slightly more, then repeat the process all over again.  You can control the playback of your animation using these simple VCR style controls:

image

 

Here is a very simple and crude kicking animation:

gif3

 

Another cool thing you can do is add Events as part of your timeline, like so:

image

image

Enabling you to create events that can be fired in code, allowing you to incorporate programmatic aspects into your animations, such as playing a footstep audio effect.  We will see this process shortly.

 

Exporting the Animation

Now that we’ve got an animation to use in our game, it’s time to export it.  Here there are a couple of choices. 

image

 

You can export your results as a video, a sequence of images or as data.  If you chose to export as an image you can actually have some rather advanced controls, including generating a texture atlas (directly usable in LibGDX) or sprite sheet:

image

 

With results like:

skeleton-kick

 

This approach can be utilized in just about every single kind of game engine available today.  However, where Spine shines is when you chose to export as data instead.  This is where runtimes come in.  These are essentially libraries or code for the various game engines that enable you to use spine format natively.  Full source is available on github and runtimes exist for most 2D engines available including Unity, LibGDX, Love, MonoGame, Torque2D, Cocos2d-x and many more.  In this example I will be using LibGDX.

 

In this case I’m going to export to JSON and generate a texture atlas using the following settings:

image

 

Now let’s break out some code.

 

Using Spine In Game

As mentioned earlier Spine have several runtimes available on github.  In the case of the LibGDX project, you simply have to copy the code into your appropriate source code folder.  Assuming you created a project using the setup utility, this means copying the contents of esotericsoftware to your core\src\com directory.  Then I wrote the following code, adapted from one of their LibGDX examples.

Make sure that you’ve exported your assets and created the atlas in your working directory, most likely \core\assets.  Then use the following code:

package com.gamefromscratch;

import com.badlogic.gdx.ApplicationAdapter;
import com.badlogic.gdx.Gdx;
import com.badlogic.gdx.graphics.GL20;
import com.badlogic.gdx.graphics.OrthographicCamera;
import com.badlogic.gdx.graphics.g2d.SpriteBatch;
import com.badlogic.gdx.graphics.g2d.TextureAtlas;
import com.esotericsoftware.spine.*;

public class Spine2 extends ApplicationAdapter {
    private OrthographicCamera camera;
    private SpriteBatch batch;
    private SkeletonRenderer renderer;
    private TextureAtlas atlas;
    private Skeleton skeleton;
    private AnimationState state;

	public void create () {
		camera = new OrthographicCamera();
        camera.setToOrtho(false);
		batch = new SpriteBatch();
		renderer = new SkeletonRenderer();
		renderer.setPremultipliedAlpha(true); // PMA results in correct blending without outlines.

		atlas = new TextureAtlas(Gdx.files.internal("skeleton.atlas"));
		SkeletonJson json = new SkeletonJson(atlas);
		SkeletonData skeletonData = json.readSkeletonData(Gdx.files.internal("skeleton.json"));
		skeleton = new Skeleton(skeletonData);
		skeleton.setPosition(0, 0);

		AnimationStateData stateData = new AnimationStateData(skeletonData);
		state = new AnimationState(stateData);

        // Set up an animation listener so we can respond to custom events or completion
        final AnimationState.TrackEntry track = state.setAnimation(0, "kick", false);
        track.setListener(new AnimationState.AnimationStateListener() {
            @Override
            public void event(int trackIndex, Event event) {
                // Check for the "half" event we defined in the editor
                if(event.getString().equals("half"))
                    System.out.println("Half way baby");
            }

            @Override
            public void complete(int trackIndex, int loopCount) {
                // or the complete event (not END!) when done, fire the idle animation instead
                state.setAnimation(0,"idle",false);
            }

            @Override
            public void start(int trackIndex) {
            }

            @Override
            public void end(int trackIndex) {
            }
        });
	}

	public void render () {
		state.update(Gdx.graphics.getDeltaTime()); // Update the animation time.
		state.apply(skeleton);
		skeleton.updateWorldTransform();

        Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT);
		camera.update();
		batch.getProjectionMatrix().set(camera.combined);
		batch.begin();
		renderer.draw(batch, skeleton);
		batch.end();
	}

	public void dispose () {
		atlas.dispose();
	}
}

 

When you run this code...

gif4

 

In the above code example you can see how you can handle an event you defined in Spine.  Otherwise it’s pretty simply to load and play animations on a character developed in Spine.  There is a comprehensive API, I’ve only touched on a very small part of it here due to space (this is already pretty long...).  There are also several features I never got to mention such as free form deformation ( useful for shapes such as capes ), swappable skins, place able props, etc..  If you are doing 2D animation, Spine is certainly a product you should check it.  Spine is by no means the only option when it comes to 2D animation in games, Spriter and Creature are two other popular alternatives.  It is however a very good option.

 

The Video

Art Programming


13. March 2016

 

BDX is a 3D engine that is hosted inside Blender and uses Java and the LibGDX library for programming.  For more information I took a pretty in-depth look at an earlier version available here.  Basically BDX installs as a Blender add-on, which you use to create your games content and levels, but you use LibGDX and Java to program your actual game.  BDX exposes several Blender features to your game, such as physics properties.

 

Details of this release are available on /r/gamedev, but the heart of the release are:

  • Saving the meshes from Blender has been optimized, which can make the starting process a ton faster.
  • Rendering to a depth texture for depth-based 2D screen shaders is now possible.
  • Additional built-in screen shaders include: Outline, Invert, and Depth-Of-Field shaders.
  • You can now color, tint, and otherwise alter individual materials on a GameObject.
  • Camera functions have been added to allow for view changes (i.e. changing the viewport width of the camera view).
  • Various bug-fixes.

It’s an interesting project, especially if you are working with Blender and Java, and is one you should consider checking out.  It is complete free and open source, released under the Apache 2 license.

GameDev News


8. February 2016

 

This story coming care of /r/gamedev, BDX released version 0.2.3.  BDX is a game engine hosted inside Blender using LibGDX and Java for game programming.  Essentially it enables you to define and create your game in Blender, including complete physics integration, while generating LibGDX code.  I did a pretty in-depth tutorial on working with BDX a while back.

In this release:

Here's a short change-log:

  • Per-pixel sun, point, and spot lighting. As it was before, you can simply create the lights in Blender to have them show up in-game, or spawn them during play.
  • Ability to turn off per-pixel lighting for lower-spec targeted platforms and devices.
  • Improvements to the profiler.
  • GameObjects can now switch the materials used on their mesh. You can specify the name of a material available in the scene in Blender, or you can directly provide a LibGDX material to use, in case you have one custom-made.
  • Various fixes and QOL improvements.

Check it out! We could always use some more feedback and testing.

It’s a cool project and if you are working in Blender and LibGDX is certainly something you should check out!

GameDev News


29. January 2016

 

Gdx-ai, an artificial intelligence library (steering, formations, pathfinding and more)  for LibGDX just release version 1.8.  From the change log:

[1.8.0]

- Updated to libgdx 1.9.1

- API Change and Addition: Pathfinding API

* Added method getIndex to the interface IndexedGraph.

* Removed classes DefaultIndexedGraph and IndexedNode.

- API Change and Addition: Behavior Tree API extended to make it easier to think and design in terms of states, see https://github.com/libgdx/gdx-ai/wiki/Behavior-Trees

* Added ability to guard any task.

* Added branch task DynamicGuardSelector.

* Now the text format supports internal sub-trees that, besides improving reuse and readability, allow you to use composite guards.

* Now the parser is able to report comments, which can be useful for certain tools such as graphical editors.

Gdx-ai can be downloaded from Github or can be installed using the GDX setup utility.

GameDev News


5. January 2016

 

LibGDX, the cross platform open source Java based gaming library, just released version 1.8 today and unlike many recent releases, there is a ton in this release.  The biggest aspect of this release is probably the change to LWJGL 3 on the backend.  LWJGL is a Light Weight (that’s the LW part) Java (the J) based Game Library (GL, tada!) that LibGDX desktop targets were built on top off.  Some of the limits of LWJGL 2 were holding back what LibGDX could do, such as multiple monitor support.

From the announcement blog post, the big wall of text of new features:

[1.8.0]
- API Change: Rewrote FreeType shadow rendering (much better).
- Added spaceX/Y to FreeType fonts.
- Higher quality FreeType font rendering.
- Hiero updated to v5, now with FreeType support and other new features!
- GlyphLayout now allocates much, much less memory when processing long text that wraps.
- Added LWJGL 3 backend, see https://github.com/libgdx/libgdx/issues/3673 for more info.
- Added Graphics#getFramebufferWidth and Graphics#getFramebufferHeight for HDPI handling
- API Change: Added HdpiUtils. Instead of calling GL20#glViewport and GL20#glScissor yourself
  please use HdpiUtils instead. It will ensure that you handle HDPI monitors correctly when
  using those OpenGL functions. On HDPI monitors, the size reported by Gdx.graphics 
  getWidth/getHeight is in logical coordinates as dictated by the operating system, usually half
  the HDPI resolution. The OpenGL drawing surface works in backbuffer coordinates at the full
  HDPI resolution. If you pass logical coordinates to glViewport and glScissor, you only 
  affect a quarter of the real backbuffer size. Use HdpiUtils instead, it will do the right thing, while letting you continue to work in logical (aka returned by Gdx.graphics.getWidth/getHeight) coordinates.
- API Change: Graphis#getDesktopDisplayMode() has been renamed to Graphics#getDisplayMode() and
  returns the current display mode of the monitor the window is shown on (primary monitor on
  all backends except LWJGL3, which supports real multi-monitor setups).
- API Change: Graphics#getDisplayModes() return the display modes of the monitor the monitor
  the window is shown on (primary monitor on all backends except LWJGL3 which supports real
  multi-monitor setups).
- API Change: Graphics#setDisplayMode(DisplayMode) has been renamed to 
  Graphics#setFullscreenMode(). If the window is in windowed mode, it will be switched 
  to fullscreen mode on the monitor from which the DisplayMode stems from.
- API Change: Graphics#setDisplayMode(int, int, boolean) has been renamed to 
  Graphics#setWindowedMode(int, int). This will NOT allow you to switch to fullscreen anymore, 
  use Graphics#setFullscreenMode() instead. If the window is in fullscreen mode, it will be
  switched to windowed mode on the monitor the window was in fullscreen mode on.
 - API Addition: Graphics#Monitor, represents a monitor connected to the machine the app is
  running on. A monitor is defined by a name and it's position relative to other connected
  monitors. All backends except the LWJGL3 backend will report only the primary monitor
 - API Addition: Graphics#getPrimaryMonitor() returns the primary monitor you usually want
  to work with.
 - API Addition: Graphics#getMonitor() returns the monitor your app's window is shown on,
  which may not be the primary monitor in >= 2 monitor systems. All backends except the 
  LWJGL3 backend will report only the primary monitor.
 - API Addition: Graphics#getMonitors() returns all monitors connected to the system. All
  backends except the LWJGL3 backend will only report the primary monitor.
 - API Addition: Graphics#getDisplayMode(Monitor) returns the display mode of the monitor
  the app's window is shown on. All backends except the LWJGL3 backend will report the
  primary monitor display mode instead of the actual monitor's display mode. Not a problem
  as all other backends run on systems with only a single monitor so far (primary monitor).
- Added option to include credentials on cross-origin http requests (used only for GWT backend).
- Added option to specify crossorigin attribute when loading images with AssetDownloader (GWT), see #3216.
- API Change: removed Sound#setPriority, this was only implemented for the Android backend. However, Android itself never honoured priority settings.
- API Change: cursor API has been cleaned up. To create a custom cursor, call Graphics#newCursor(), to set the custom cursor call Graphics#setCursor(), to set a system cursor call Graphics#setSystemCursor(). The Cursor#setSystemCursor method has been removed as that was not the
right place. Note that cursors only work on the LWJGL, LWJGL3 and GWT backends. Note that system cursors only fully work on LWJGL3 as the other two backends lack a means to set a specific system cursor. These backends fall back to displaying an arrow cursor when setting any system cursor.
- API Addition: Added Lwjgl3WindowListener, allows you to hook into per-window iconficiation, focus and close events. Also allows you to prevent closing the window when a close event arrives.
 


There are a lot more details available on the announcement post if you want more details on the specifics of the update. 

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