Modifying textures using libGDX Pixmap in runtime - Explained

We have previously shown a bit how we were using LibGDX Pixmap to modify textures in runtime here and here for a game prototype we were doing. In this post I want to share more detail of how we do that. The objective was to make destructible terrain like in Worms 2.

Introduction

When you work with OpenGL textures, you can't directly modify their pixels whenever you want since they are on OpenGL context. To modify them you have to upload an array of bytes using glTexImage2D or glTexSubImage2D. The problem is you have to maintain on the application side an array of bytes representing the modifications you want to do.

To simplify working with byte arrays representing images, LibGDX provides a useful class named Pixmap which is a map of pixels kept in local memory with some methods to interact with a native library to perform all modifications with better performance.

Moving data from Pixmap to OpenGL Texture

In our prototypes, we wanted to remove part of the terrain whenever a missile touches it, like a Worms 2 explosion. That means we need some way to detect the collisions between the missile and the terrain and then a way to remove pixels from a texture.

We simplified the first problem by getting the color of the pixel only for the missile's position and checking if it was transparent or not. A more correct solution could be using a bitmap mask to check collisions between pixels but we wanted to simplify the work for now.

For the second problem, given a radius of explosion of the missile, we used the pixmap fillCircle method by previously setting the color to (0,0,0,0) (fully transparent) and disabled Pixmap blending to override those pixels.

But that only modified the pixmap data, now we needed to modify the OpenGL texture. To do that, we called OpenGL glTexImage2D using the bytes of the pixmap as the new texture data and that worked correctly.

Transforming from world coordinates to Pixmap coordinates

One problem when working with pixmaps is we have to map world coordinates (the position of the missile for example) to coordinates inside the Pixmap.


This image shows the coordinate system of the Pixmap, it goes from 0 to width in x and 0 to height in y.


This image shows how we normally need to move, rotate and resize the Pixmap in a game.

To solve this, we are using a LibGDX Sprite to maintain the Pixmap transformation, so we can easily move, rotate and scale it. Then, we can use that information to project a world coordinate to Pixmap coordinate by applying the inverse transform, here is the code:

	public void project(Vector2 position, float x, float y) {
		position.set(x, y);

		float centerX = sprite.getX() + sprite.getOriginX();
		float centerY = sprite.getY() + sprite.getOriginY();

		position.add(-centerX, -centerY);

		position.rotate(-sprite.getRotation());

		float scaleX = pixmap.getWidth() / sprite.getWidth();
		float scaleY = pixmap.getHeight() / sprite.getHeight();

		position.x *= scaleX;
		position.y *= scaleY;

		position.add( //
				pixmap.getWidth() * 0.5f, //
				-pixmap.getHeight() * 0.5f //
		);

		position.y *= -1f;
	}

(note: it is the first version at least, it could have bugs and could be improved also)

To simplify our work with all this stuff, we created a class named PixmapHelper which manage a Pixmap, a Texture and a Sprite, so we could move the Sprite wherever we wanted to and if we modify the pixmap through the PixmapHelper then the Texture was automatically updated and hence the Sprite (since it uses internally the Texture).

The next video shows how we tested the previous work in a prototype were we simulated cluster bombs (similar to Worms 2):

Some adjustments to improve performance

Instead of always working with a full size Pixmap by modifying it and then moved to the OpenGL texture, we created smaller Pixmaps of fixed sizes: 32x32, 64x64, etc. Then, each time we needed to make an explosion, we used the best Pixmap for that explosion and then we called glTexSubImage2D instead glTexImage2D to avoid updating untouched pixels. One limitation of this modification is we have to create and maintain several fixed size pixmaps depending on the modification size. Our current greater quad is 256x256 (almost never used).

Then, we changed to store each modification instead performing them in the moment the PixmapHelper erase method was called, and we added an update method which performs all modifications together. This improvement allow us to call Pixmap update method when we wanted, maybe one in three game updates or things like that.

Conclusion

Despite using LibGDX Pixmap for better performance, moving data to and from OpenGL context is not a cheap operation, on Android devices this could means some pauses when refreshing the modified textures with the new data. However, there is a lot of space for performance improvement, some ideas are to work only with pixmap of less bits instead RGBA8888 and use that one as the collisions context and as the mask of the real image (even using shaders), between other ideas.

Finally, the technique looks really nice and we believe that it could be used without problems for a simple game but it is not ready yet to manage a greater game like Worms 2.

Hope you like the technique and if you use it, maybe even also share your findings.

P.S.: In case you were wondering: yes, I love Worms 2.

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Scripting with Artemis Entity System Framework

Artemis is a component based entity system framework made in Java by Arni Arent (appel) and Tiago Costa (spiegel).

The core of Artemis is small and it is based on four main concepts. The Component, where all information about an Entity is stored. The Entity, which represents a game object. The EntitySystem, where custom logic, for entities with one or more component, is processed. And finally the World, where Entities and EntitySystems live. The idea is to grow over those concepts by making your own Components and EntitySystems.

The problem

There are some cases where it depends a lot how are you using Artemis, to feel it is helping you or not. For example, when you want an Entity to have some custom behavior on a specific level you could follow the next approach.

First, create an SpecificBehaviorForLevelComponent to declare that an Entity with that component will have that custom behavior and then create the SpecificBehaviorForLevelSystem which performs the logic.

The problem with this approach is that you will have an empty Component used only as a mark to let the EntitySystem work over it. Also, you will have an EntitySystem that will perform logic only in a specific moment of the game and then it will be useless.

If you have to create more than just one custom behavior, then you are a bit doomed and you will hate Artemis. However, it is not Artemis, or any component based entity framework, fault.

Script Framework, a possible solution

To simplify working with cases like the one mentioned before, we created a scripting framework over Artemis, composed by three main concepts: the Script, the ScriptComponent and the ScriptSystem.

Script

This is an interface which provides the following three methods:

  • init(world, entity) : called once when the entity enters the world.
  • update(world, entity) : called in each world update
  • dispose(world, entity) : called once when the entity leaves the world.

It should be implemented and added to the ScriptComponent of an Entity in order to perform the behavior.

ScriptComponent

This is an Artemis Component which contains a collection of Scripts and it is used by the ScriptSystem in order to know which Scripts to process on each Entity.

ScriptSystem

This is an Artemis EntitySystem responsible of calling, for each Entity, the init/update/dispose methods of each Script declared in the ScriptComponent of that Entity.

For the previous example, where we wanted a specific behavior for an entity in one level, we could create a SpecificBehaviorForLevelScript and, when loading that level, add that script to the ScriptComponent. So, instead creating Components and EntitySystems, we can create only Scripts.

Pros

  • Clear and simple API.
  • Easy to add/remove a Script vs add/remove a System.
  • Scripts are easily reusable (when you want two or more entities with a custom behavior).
  • Logic localized in one place.
  • Allow different implementations of the Script interface, for example, a Groovy implementation.

Cons

  • Not good for global stuff like rendering, an EntitySystem keeps being better for those cases.
  • Hard to know the right balance between which code should be on Scripts and which one on Systems.

Conclusion

The Script Framework is some point in the middle between Entities with no logic at all and Entities with all the logic. It should be used with care, learning to balance which code should be on Scripts and which code on Systems is not easy.

Artemis is only a small core, a foundation of classes to work with. The real power comes from the custom Components and Systems you create over it. For example, in our case we created several Systems that we reuse between games, some of them are the RenderSystem responsible of rendering the entities with the RenderComponent using libGDX and the PhysicsSystem responsible of processing the Box2d world.

References

There are a lot of resources about components based entity systems, however the best/correct solution between all these references is not so clear.

Hope you like it.

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Quick prototyping and sharing FTW!!

Since the beginning of times (of Gemserk), I had one or more local projects where I could test stuff related to the libraries we were using (Slick2D, LibGDX, Artemis), graphical effects, game ideas or just algorithms. One example is the lighting bolt effect I talked about in a previous post, I have also made some videos of some other tests but never uploaded the code.

As these kind of prototypes could be useful for other developers we have started a new project named prototypes (yeah, super creative name) where we (at least I) are going to add some of the new tests and prototypes we make.

To be easily tested by anyone, we created a Webstart and an Android application with a launcher to select which test or prototype you want to run.

Hope you like it.

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Super Flying Thing - Update 09

There is a new version of Super Flying Thing available, here is the change log:

  • Changed to count the best time to end a level
  • Modified random level generation and changed random mode to be named training
  • Removed practice mode, go to training now
  • Removed Exit button, you can exit the game pressing back button on main menu
  • Added sound for the explosions
  • Added about us screen with links to blog and more games

Remember, you can play it right now, just follow the next links:

PLAY ON PC or PLAY ON ANDROID:

Play on Android

Hope you enjoy it.

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First version of new random level generator for Super Flying Thing

Two weeks ago I was working to improve random level generation of Super Flying Thing, the objective was to make the levels a bit more interesting.

Previous generator was really simple, the idea was to define where the starting and destination planet will be and then generate a lot of "garbage" in the way, sometimes with no possible path between both planets.

New level generator does more work to generate a bit more interesting level. Basically the idea is to use some pre generated tiles:

Tiles are defined by SVG groups in a SVG file with custom meta data defining with which tile can be paired.

Based on that information, the generator creates a pattern and based on that pattern and the tiles, it creates the level.

For example, if we have four tiles {A, B, C, D} where A is the where the start planet should be and D where the destination planet should be, and we have the possible links {A -> B, A -> C, B -> B, B -> C, B -> D, C -> B, C -> C, C -> D}, then a possible level could be ABBCBCD (using a regular expression could be defined with something like A(B|C)+D).

So, a very basic pseudo algorithm could be something like this:

	tiles.add(startTile)
	currentTile = startTile
	while (currentTile != endtile) {
		tile = getPossibleNextTile(currentTile);
		tiles.add(tile);
		currentTile = tile;
	}

Where getPossibleNextTile() method uses the meta data of the tile to define randomly a possible next tile.

Here is how a random generated level looks like:

As the title says, this is the first version of the generator, there are a lot of possible improvements to be made and/or create a new generator and throw this one to the trash can.

After writing the post I realized that there is not so much information and the algorithm is pretty basic but I hope it could be of help anyway.

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What's going on with the Super Flying Thing?

On the last weeks I was a bit distracted working on Vampire Runner and with Mad Jetpack so I ended up kinda leaving Super Flying Thing abandoned, I also have some doubts about which features to work on so I preferred to dedicate time on other projects while deciding what to do with the game.

Super Flying Thing is really fun to me, I love the concept but right now the game could be a bit boring and I want to improve that, not so sure how, but I want to try some ideas I have in mind.

About levels

The main idea of the game is you have to master your flying skills and for that you have to try and fail a lot of times. For that reason, I want to modify the levels to be smaller and harder but not frustrating since you can quickly try again and again.

Random levels are now generated using pre generated tiles (I want to talk about this in a dedicated post), so they are a bit more interesting, however they don't transmit the idea of try and fail a lot of times yet, so I have to work a bit on level generation.

About game modes

The practice mode will be removed since you can practice in both challenge and random modes. However, for starters I want to add a Tutorial where you can test the controls and learn how to play to mitigate the change I plan to do over the levels.

Also, we want to try an Endless mode where you have to go as far as you can, playing through different challenges each time harder and harder.

About content

On some levels there are lasers, moving obstacles and even portals. Despite I love all this stuff, I will probably remove them until I see how they really fit in the game.

Stars will be probably removed as well since they don't contribute nothing to the game for now. Again, this will be probably temporary until it fits in the game.

About game objective

On normal game mode, the main objective will remain the same, travel from one planet to the other. However, I want to add a second objective to add challenge factor to the game, something to make the player want to try again the same level several times. One possibility is to add some kind of local competition, for example, improve the time to reach the destination planet, play against your best time, or something like this. Going further with that possibility, maybe publish that replay/best score online and compete with others.

We have to dig further in this subject since it can contribute with re playability factor.

About controls

Now that we fixed the game behaving different on different devices I will rip off the AxisController and the TiltController and probably one more, and leave only the original one plus maybe some other.

The original control was modified a bit in order to let the player control the ship better based on how new levels are going to be.

Conclusion

That's all for now, the idea of this post is to let you know that I want to to continue this game.

Hope you liked it, even if it has nothing interesting.

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Testing Android controls on libGDX PC application using libGDX remote

When testing our games, sometimes we only need to test the game controls on the Android devices, not all the game, and deploying it on the device is always slower than running it on the PC.

The LibGDX library provides a way to send your Android device input data to through the network, one of the possible uses is to control your libGDX PC application with it.

Here is a demo video using the remote input, made by libGDX team:


(note: magic starts after minute 2)

In the case of Super Flying Thing, we need it when testing and debugging some controls that cannot be tested directly on PC like the TiltController for example (we need device orientation data). Recently, we starting using it also to test and customize other controls like the the ClassicController (despite it has a bit of lag in some cases).

Sadly, my camera is also my android phone so I can't make a video of how we are using it.

One interesting point of this is that we could use multiple android devices (and probably other devices like iPod/iPhone/iPad/others) to create multiple wireless controllers for PC, and that, for example, could be funny if we want to make a local multiplayer game.

Another interesting point is that you could implement your own remote input server to read the device input data sent by the GDX Remote Android Application, so you wouldn't be forced to use libGDX in your server application.

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Super Flying Thing - Update 08

There is a new version of Super Flying Thing available, here is the change log:

  • Added replays to show how you died a lot of times :P, could be disabled if you don't want to watch it.
  • Changed the Splash screen to load all stuff once to improve performance during the game and to show loading progress.
  • Changed screen buttons, moved them up to avoid touching the ads when trying to touch a button.
  • Changed to avoid showing a title bar when the game started.
  • Changed Settings screen, moved controllers stuff to another screen.
  • More performance improvement.
  • Fixed (probably) the bug of OutOfMemoryException when the game was left open for a long time.

Remember, you can play it right now, just follow the next links:

PLAY ON PC or PLAY ON ANDROID:

Play on Android

Hope you enjoy it.

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Super Flying Thing - Update 07

Hi everyone, we found a little tiny bug that made our game run different in different phones, so in some phones the ship would move way faster than in others, and that make the game a little too challenging (impossible to control, always dying, lots of fun).

The other big changes in this updates are some stuff trying to get the game to run better on phones that aren't the latest and greatest. For now the background will start disabled but you can enable it by going to the settings page (it looks really nice 🙂 but it is expensive to show in some phones, in the future we will try to test the phone or start with the background enabled and detect if it is an issue and suggest to the user that he can disable it to get better performance).

As always, a change log:

  • Fixed a bug making the game run different on different devices, some times almost not playable
  • Added settings to enable/disable background to improve game performance (disabled by default)
  • Added new controller named TargetController which allows you to specify the point the ship should go
  • Added a second background which moves with the camera giving a basic idea of parallax
  • Changed ship animation to have more frames to be smoother
  • Changed internal stuff to improve performance.
  • Changed the graphics (background, walls, color of portals)

Also, we have a new gameplay video:

Remember, you can play it right now, just follow the next links:

PLAY ON PC or PLAY ON ANDROID:

Play on Android

Hope you enjoy it.

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Super Flying Thing - Update 06

Readers, I know there are some, there is a new update of the game, should be available on Android Market already.
We added different controllers and we are testing how they feel and what method of control people like best.

As always, a change log:

  • Added more levels and fixed previous ones.
  • Added different controllers to test.
  • Added level preview on level selection screen.
  • Added settings screen which lets you choose different controllers and test them.
  • Added message to show which level is being previewed
  • Added animation to visited planet to differentiate easily between start and destination planets.
  • Changed ship to receive damage instead killing it instantly, so you now could survive in some cases.
    Fixed a bug with lasers.

Remember, you can play it right now, just follow the next links:

PLAY ON PC or PLAY ON ANDROID:

Play on Android

Hope you enjoy it.

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Rating: 5.0/5 (2 votes cast)