Recomendados
Recomendados
Más contenido relacionado
La actualidad más candente
La actualidad más candente (20)
Destacado
Similar a Box2D and libGDX
Similar a Box2D and libGDX (20)
Más de Jussi Pohjolainen
Más de Jussi Pohjolainen (19)
Último
Último (20)
Box2D and libGDX
- 1. Box2D and libGDX Jussi Pohjolainen Tampere University of Applied Sciences
- 2. Box2D • Free open source 2D physics simulator engine wriEen in C++ • Has been used for example in Angry Birds, Tiny Wings • Has been ported to Java, Flash, C#, JavaScript • Programs that use Box2D – libGDX, Unity, iOS SpriteKit, GameMaker Studio ...
- 3. Concepts • World – CollecNon of bodies, fixtures, joints that interact • Body – Game Objects that contains fixtures – Dynamic (spaceship), StaAc (ground) and KinemaAc – Fixture • Body has Fixture! • Density: Mass per square meter: bowling ball dense, balloon not • FricAon: When sliding along something, amount of opposite force • ResAtuAon: How bouncy object is (0 = does not bounce, 1 = very bouncy) • Shape – Fixture has Shape – Polygon or Circle, can be mixed • Joint – Holds bodies together. Several joints available.
- 4. World Body Fixture Shape // Create array full of bodies Array<Body> bodies = new Array<Body>(); // Take all bodies from world and put them into array world.getBodies(bodies); // Get shape of first body, it's first fixture and it's shape Shape s = bodies.get(0).getFixtureList().get(0).getShape();
- 5. Units • Box2D uses floaAng points • Tuned for meter – kilogram – second (KMS) • OpNmized so that shapes can move between 0.1 – 10 meters • It's tempNng to use pixel as units -‐> leads to poor simulaNon and weird behavior – Keep moving objects between 0.1 – 10 meters! • DO NOT USE PIXELS! DO NOT!
- 6. Units in libGDX • Window/real resoluNon <-‐> World Units <-‐> Box2D units (meters) • How to handle this? Just use meters in World Units, so you don't have to make any conversions – float width = 640.0f / 100.0f – float height = 400.0f / 100.0f – camera = new OrthographicCamera(); – camera.setToOrtho(false, width, height);
- 7. CreaNng a World // Create world and set it's gravity! // true => allow body sleeping World world = new World(new Vector2(0, -9.8f), true); // Next steps: create a body to the world
- 8. Body Types • Dynamic Body – Player and other actors on screen • StaAc Body – Walls, floors and so on • KinemaAc Body – Moving pladorm in pladorm game – It's a staNc body that can also move and rotate. When dynamic body collides, kinemaNc body "wins"
- 9. Bodies • Bodies are objects in physics space – Does not hold texture! So it's not visible! • Hold properNes like – mass, velocity, locaNon, angle • Define size and shape of the body using a fixture • Shape can be circle or polygon or a mixture of these!
- 10. CreaNng a Body • To create body, use – // Create BodyDef.. – Body playerBody = world.createBody(BodyDef); • BodyDef? – Type of body? StaNc, kinemaNc, dynamic – PosiNon • Ager creaNon, add a Fixture to the body – Density, ResNtuNon (bouncy?), fricNon (slippery?), shape (circle or polygon) – playerBody.createFixture(playerFixtureDef);
- 11. CreaNng a Body public void createPlayerBody() { // *** 1) DEFINITION OF A BODY *** / // Body Definition BodyDef myBodyDef = new BodyDef(); // It's a body that moves myBodyDef.type = BodyDef.BodyType.DynamicBody; // Initial position is centered up (width = 12.8, height = 7.2) // This position is the CENTER of the shape! myBodyDef.position.set(WORLD_WIDTH / 2, WORLD_HEIGHT / 2); // *** 2) CREATE THE BODY *** / Body playerBody = world.createBody(myBodyDef);
- 12. // *** 3) FIXTURE FOR THE BODY *** / // Create fixture and add the shape to it FixtureDef playerFixtureDef = new FixtureDef(); // Mass per square meter (kg^m2) playerFixtureDef.density = 1; // How bouncy object? Very bouncy [0,1] playerFixtureDef.restitution = 1.0f; // How slipper object? [0,1] playerFixtureDef.friction = 0.5f; // Create circle shape. CircleShape circleshape = new CircleShape(); circleshape.setRadius(0.1f); // Add the shape to the fixture playerFixtureDef.shape = circleshape; // Add fixture to the body playerBody.createFixture(playerFixtureDef); }
- 13. About Rendering • Box2D holds the physics, it's not about rendering – For every render call, update (step) the world • To render, map some texture to the posiNon of the playerBody! • For debugging, use debugRenderer
- 14. Example About Rendering public class Box2DExample extends ApplicationAdapter { private SpriteBatch batch; public static final boolean DEBUG_PHYSICS = true; public static final float WORLD_WIDTH = 6.4f; public static final float WORLD_HEIGHT = 4.0f; private OrthographicCamera camera; private World world; private Box2DDebugRenderer debugRenderer; @Override public void create () { camera = new OrthographicCamera(); camera.setToOrtho(false, WORLD_WIDTH, WORLD_HEIGHT); batch = new SpriteBatch(); world = new World(new Vector2(0f, -9.81f), true); debugRenderer = new Box2DDebugRenderer(); createPlayerBody(); } public void createPlayerBody() { ... } @Override public void render () { batch.setProjectionMatrix(camera.combined); Gdx.gl.glClearColor(1, 0, 0, 1); Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT); if(DEBUG_PHYSICS) { debugRenderer.render(world, camera.combined); } batch.begin(); // Do some drawing batch.end(); world.step(1/60f, 6, 2); } }
- 15. Rendering (Debug) // Create the renderer (in create...) Box2DDebugRenderer debugRenderer = new Box2DDebugRenderer(true, // draw bodies false, // joints false, // drawAABBs false, // drawInactiveBodies false, // drawVelocities false); // drawContacts public void render() { ... debugRenderer.render(world, camera.combined); world.step(1 / 60f, 6, 2); ... }
- 16. Update World: Stepping • To update world, we need to tell the world to step // Advance simulation 1/60 of a sec. This should // correspond to framerate in your game float timeStep = 1/60.0f; // How strongly to correct velocity when colliding // More higher, more correct simulation but cost of performance int velocityIterations = 6; // How strongly to correct position when colliding // More higher, more correct simulation but cost of performance int positionIterations = 2; world.step(timeStep, velocityIterations, positionIterations); • Do this at the end of the render() call
- 17. Variable Nmestep • If you have following – world.step(1/60f, 6, 2); • SimulaNon can be ruined if machine is not able to run at 60fps • You could calculate the game speed and add it to stepping – world.step(framerate, 6, 2); • Problem now is that your game can run very very fast or very very slow
- 18. public void render() { ... doPhysicsStep(); } private double accumulator = 0; private double currentTime = TimeUtils.millis() / 1000.0; private void doPhysicsStep() { // We are not using Gdx.graphics.getDeltaTime(), it may not // be accurate enough. // Current time double newTime = TimeUtils.millis() / 1000.0; // How much time since last call? double deltaTime = newTime - currentTime; currentTime = newTime; float TIME_STEP = 1/60f; // If it took ages (> 0.25 => 4 fps) // FIXED Upper limit to prevent going really slow if(deltaTime > 0.25) { deltaTime = 0.25; } accumulator += deltaTime; while (accumulator >= TIME_STEP) { world.step(TIME_STEP, 6, 2); accumulator -= TIME_STEP; } }
- 19. "Ground" public void createGround() { // *** 1) DEFINITION OF A BODY *** / // Body Definition BodyDef myBodyDef = new BodyDef(); // This body won't move myBodyDef.type = BodyDef.BodyType.StaticBody; // Initial position is centered up // This position is the CENTER of the shape! myBodyDef.position.set(WORLD_WIDTH / 2, 0.25f); // *** 2) CREATE THE BODY *** / Body groundBody = world.createBody(myBodyDef); // *** 3) FIXTURE FOR THE BODY *** / // Create shape PolygonShape groundBox = new PolygonShape(); // Real width and height is 2 X this! groundBox.setAsBox( WORLD_WIDTH/2 , 0.25f); // Add shape to fixture, 0.0f is density. // Using method createFixture(Shape, density) no need // to create FixtureDef object as on createPlayer! groundBody.createFixture(groundBox, 0.0f); }
- 20. Draw texture to body pos! public void render() { ... batch.draw(texture, playerBody.getPosition().x, playerBody.getPosition.y); }
- 21. Draw texture to body pos! batch.draw(playerTexture, playerBody.getPosition().x - playerRadius, playerBody.getPosition().y - playerRadius, playerRadius, // originX playerRadius, // originY playerRadius * 2, // width playerRadius * 2, // height 1.0f, // scaleX 1.0f, // scaleY playerBody.getTransform().getRotation() * MathUtils.radiansToDegrees, 0, // Start drawing from x = 0 0, // Start drawing from y = 0 playerTexture.getWidth(), // End drawing x playerTexture.getHeight(), // End drawing y false, // flipX false); // flipY
- 22. Create Body and Add User Data public void createJussi(float x, float y) { BodyDef bodyDef = new BodyDef(); bodyDef.type = BodyType.DynamicBody; bodyDef.position.set(x,y); Body body = world.createBody(bodyDef); PolygonShape dynamicCircle = new PolygonShape(); dynamicCircle.setAsBox(0.5f, 0.5f); FixtureDef fixtureDef = new FixtureDef(); fixtureDef.shape = dynamicCircle; fixtureDef.density = 1.0f; fixtureDef.friction = 0.1f; fixtureDef.restitution = 0.8f; body.createFixture(fixtureDef); // user data can be anything! any object! body.setUserData(jussiTexture); }
- 23. Create Body and Add User Data public void render() { ... debugRenderer.render(world, camera.combined); // populate the array with bodies world.getBodies(bodies); // iterate the bodies for (Body body : bodies) { if(body.getUserData() != null && body.getUserData() == jussiTexture) { batch.draw((Texture) body.getUserData(), body.getPosition().x - 0.5f, body.getPosition().y - 0.5f, ... body.getTransform().getRotation() * MathUtils.radiansToDegrees, ... false ); } } doPhysicsStep(); }
- 25. Forces and Impulses • To move things around, you'll need to apply forces or impulses to a body • Force – Gradually over Nme change velocity of a body – Also angular force available, torque (twisNng strength) • Impulse – Change velocity immediately • Of course you can just change the posiNon of a body
- 26. Examples // gradually accelerate right body.applyForceToCenter(50f, 0, true); // Jump up body.applyLinearImpulse(new Vector2(0f, 20f), body.getWorldCenter(), true);
- 27. COLLISIONS
- 28. Collision world.setContactListener(new ContactListener() { @Override public void beginContact(Contact contact) { Body bodyA = contact.getFixtureA().getBody(); Body bodyB = contact.getFixtureB().getBody(); } @Override public void endContact(Contact contact) { } @Override public void preSolve(Contact contact, Manifold oldManifold) { } @Override public void postSolve(Contact contact, ContactImpulse impulse) { } });