In this post I describe the steps to create a domino effect in Android. I have used Box 2D which is a physics game engine and AndEngine. The simulation is based on a demo in Java by Daniel Murphy in his site http://www.jbox2d.org/. There is a great tutorial on Box2D at http://www.iforce2d.net/b2dtut/introduction. Box2D is a really powerful 2D physics engine with collision detection, friction and restitution and all the good things of nature.
In this post I deal with some of the basic concepts of Box2D engine. At the most basic level is the ‘Body’. A body has linear,angular velocity,mass, location etc. It is then assigned a ‘shape’ which can be circle or polygon and finally we have assign the bodies to fixtures which carry properties of friction, restitution, density (density x area = mass), etc.
Finally all bodies are part of the ‘world’.
You can take a look at the domino effect in the video clip – domino clip
The entire project can be cloned from GitHub at Dominoes
So for the domino effect I create floor,roof,left and right walls which are the shapes
//Create the floor
final VertexBufferObjectManager vertexBufferObjectManager = this.getVertexBufferObjectManager();
final Rectangle ground = new Rectangle(0, CAMERA_HEIGHT – 2, CAMERA_WIDTH, 2, vertexBufferObjectManager);
final Rectangle roof = new Rectangle(0, 0, CAMERA_WIDTH, 2, vertexBufferObjectManager);
final Rectangle left = new Rectangle(0, 0, 2, CAMERA_HEIGHT, vertexBufferObjectManager);
final Rectangle right = new Rectangle(CAMERA_WIDTH – 2, 0, 2, CAMERA_HEIGHT, vertexBufferObjectManager);
The body with the fixture is
final FixtureDef wallFixtureDef = PhysicsFactory.createFixtureDef(0, 0.5f, 0.5f);
PhysicsFactory.createBoxBody(this.mPhysicsWorld, ground, BodyType.StaticBody, wallFixtureDef);
PhysicsFactory.createBoxBody(this.mPhysicsWorld, roof, BodyType.StaticBody, wallFixtureDef);
PhysicsFactory.createBoxBody(this.mPhysicsWorld, left, BodyType.StaticBody, wallFixtureDef);
PhysicsFactory.createBoxBody(this.mPhysicsWorld, right, BodyType.StaticBody, wallFixtureDef);
Similarly I create 3 platforms on which I array vertical bricks.
The shape is created by creating a sprite.
platform1 = new Sprite(50, 100, this.mPlatformTextureRegion, this.getVertexBufferObjectManager());
The platform body is created as follows
platformBody1 = PhysicsFactory.createBoxBody(this.mPhysicsWorld, platform1, BodyType.StaticBody, FIXTURE_DEF);
The FIXTURE_DEF is the fixture which is defined as
privatestaticfinal FixtureDef FIXTURE_DEF = PhysicsFactory.createFixtureDef(50f, 0.1f, 0.5f);
where the parameters 50f,0.1f,0,5f correspond to density, coefficient of restitution and friction.
The platform is then added to the scene
this.mScene.attachChild(platform1);
I stack 37 vertical bricks on the platform
// Create 37 bricks
for(int i=0; i < 37; i++) {
brick = new Sprite(50 + i * 15, 50, this.mBrickTextureRegion, this.getVertexBufferObjectManager());
brickBody = PhysicsFactory.createBoxBody(this.mPhysicsWorld, brick, BodyType.DynamicBody, FIXTURE_DEF);
…
this.mPhysicsWorld.registerPhysicsConnector(new PhysicsConnector(brick, brickBody, true, true));
this.mScene.attachChild(brick);
brick.setUserData(brickBody);
}
I tilt the first few bricks to create the domino effect as follows
float angle = brickBody.getAngle();
Log.d(“Angle”,“angle:”+ angle);
// Tilt first 4 bricks
if (i == 0 || i == 1 || i == 2 || i == 3 || i == 4) {
brickBody.setTransform(120/PIXEL_TO_METER_RATIO_DEFAULT,80/PIXEL_TO_METER_RATIO_DEFAULT,(65 – (i*10)) * DEGTORAD);
}
Note: The PIXEL_TO_METER_RATIO_DEFAULT which divides the units.
I tried to make the end of the domino effect in the 1st platform trigger the domino effect in the 2nd which would trigger in the 3rd. However I could not make it happen consistently. So I trigger the domino effect in each of the 3 platforms by tilting the first few bricks.
Anyway it was good fun.
You can take a look at the domino effect in the domino clip
The entire project can be cloned from Dominoes
Take a look at some cool simulations using AndEngine & Box2D
1. Bull in a china shop – Behind the scenes in android
2. Creating a blob in Android using Box2D physics Engine & AndEngine
3. The making of Total Control Android game
4. Simulating an Edge Shape in Android
5. Simulating a Web Joint in Android
6. Modeling a Car in Android
7. Fun simulation of a Chain in Android
8. “Is it animal? Is it an insect?” in Android
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