Perpetuum Mobile
Good afternoon, dear user habr.com! This is the third article on the topic. I work all day long, I can not tear myself away from the amazing Box2D library.
If you have not read the first and second articles, be sure to look, it will be fun! I work in Eclipse , I write in Java. Why did I name my article this way? Read on - and very soon everything will become clear! Spoiler: we'll make your perpetual motion machine (including for the machine), and, perhaps, we will create the machine itself!
Figure 1. Perpetuum mobile.
So today we try to get something like this:
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Figure 2. The machine with the engine.
Yes, this is not a typo! Today we will make a car with a real engine, it will be indistinguishable from the real one! This is not a “cart” from the first article.
See the first article on connecting libGDX .
Here is an image with a demonstration of how my build looks. I added the Utils package to the Core folder with the class Constants, which contains only one constant - the number of pixels per meter. This is so that the world is not gigantic.
Figure 3. My build.
Here is the code for the DesktopLauncher class from the com.mygdx.game.desktop package:
The following code is for the MyGdxGame class from the com.mygdx.game package. Everything is in the comments to the code.
Figure 4. What do we get when compiling?
We create our car engine that turns its wheels. But it works forever, because there is no energy loss. So we create our perpetual motion machine!
And you wonder what is at the end of the level? Send screenshots in the comments as you pass. Thank you for reading the article to the end! I hope you can create your car in Box2D!
PS Waiting for your questions in the comments! Long live the game physics!
If you have not read the first and second articles, be sure to look, it will be fun! I work in Eclipse , I write in Java. Why did I name my article this way? Read on - and very soon everything will become clear! Spoiler: we'll make your perpetual motion machine (including for the machine), and, perhaps, we will create the machine itself!
Figure 1. Perpetuum mobile.
So today we try to get something like this:
')
Figure 2. The machine with the engine.
Yes, this is not a typo! Today we will make a car with a real engine, it will be indistinguishable from the real one! This is not a “cart” from the first article.
See the first article on connecting libGDX .
Here is an image with a demonstration of how my build looks. I added the Utils package to the Core folder with the class Constants, which contains only one constant - the number of pixels per meter. This is so that the world is not gigantic.
Figure 3. My build.
Here is the code for the DesktopLauncher class from the com.mygdx.game.desktop package:
Paste this code into the class and forget about it.
package com.mygdx.game.desktop; import com.badlogic.gdx.backends.lwjgl.LwjglApplication; import com.badlogic.gdx.backends.lwjgl.LwjglApplicationConfiguration; import com.mygdx.game.MyGdxGame; public class DesktopLauncher { public static void main(String[] arg) { LwjglApplicationConfiguration config = new LwjglApplicationConfiguration(); // config.width = 720; // config.height = 480; config.backgroundFPS = 60; config.foregroundFPS = 60; new LwjglApplication(new MyGdxGame(), config); } } The following code is for the MyGdxGame class from the com.mygdx.game package. Everything is in the comments to the code.
Create a world and typewriter.
package com.mygdx.game; import com.badlogic.gdx.ApplicationAdapter; import com.badlogic.gdx.Gdx; import com.badlogic.gdx.Input.Keys; import com.badlogic.gdx.graphics.GL20; import com.badlogic.gdx.graphics.OrthographicCamera; import com.badlogic.gdx.math.Vector2; import com.badlogic.gdx.math.Vector3; import com.badlogic.gdx.physics.box2d.Body; import com.badlogic.gdx.physics.box2d.BodyDef; import com.badlogic.gdx.physics.box2d.Box2DDebugRenderer; import com.badlogic.gdx.physics.box2d.CircleShape; import com.badlogic.gdx.physics.box2d.FixtureDef; import com.badlogic.gdx.physics.box2d.PolygonShape; import com.badlogic.gdx.physics.box2d.World; import com.badlogic.gdx.physics.box2d.joints.RevoluteJointDef; import utils.Constants; public class MyGdxGame extends ApplicationAdapter { private OrthographicCamera camera; private boolean DEBUG = false; private World world; private Box2DDebugRenderer b2dr; // private Body box; // private Body backweel; // private Body frontweel; private Body floor; private Body triangle; // private float m = -20; public void create() { float w = Gdx.graphics.getWidth(); float h = Gdx.graphics.getHeight(); camera = new OrthographicCamera(); camera.setToOrtho(false, w / 2, h / 2); world = new World(new Vector2(0, -9.8f), false); b2dr = new Box2DDebugRenderer(); // floor = createFloor(); // triangle = createTriangle(20f, 40f, 30f, -2f, -2f, 5f); triangle = createTriangle(50f, 60f, 80f, -2f, 10f, -2f); triangle = createTriangle(100f, 160f, 200f, -2f, 20f, -2f); triangle = createTriangle(280f, 290f, 300f, -2f, 100f, -2f); // box = createBox(); // backweel = createWeel(-1f, 2f); frontweel = createWeel(4.5f, 2f); // connected(); } // public void connected() { revJoint(box, backweel, -1f * 10 / utils.Constants.PPM, -2f * 10 / utils.Constants.PPM); revJoint(box, frontweel, 4.5f * 10 / utils.Constants.PPM, -2f * 10 / utils.Constants.PPM); } // ! ! public void revJoint(Body body1, Body body2, float xo, float yo) { // RevoluteJointDef rjd = new RevoluteJointDef(); // rjd.enableMotor = true; // . , , // . . - ! rjd.motorSpeed = m; // rjd.maxMotorTorque = 30; rjd.collideConnected = false; rjd.bodyA = body1; rjd.bodyB = body2; rjd.localAnchorA.set(xo, yo); world.createJoint(rjd); } public void render() { update(Gdx.graphics.getDeltaTime()); Gdx.gl.glClearColor(0, 0, 0, 1); Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT); b2dr.render(world, camera.combined.scl(Constants.PPM)); } public void resize(int width, int height) { camera.setToOrtho(false, width / 2, height / 2); } public void dispose() { world.dispose(); b2dr.dispose(); } public void update(float delta) { world.step(1 / 60f, 6, 2); cameraUpdate(delta); inputUpdate(delta); } // , public void inputUpdate(float delta) { if (Gdx.input.isKeyPressed(Keys.SPACE)) { box.setLinearVelocity(5, 5); } } // public void cameraUpdate(float delta) { Vector3 position = camera.position; position.x = box.getPosition().x * Constants.PPM; position.y = box.getPosition().y * Constants.PPM; camera.position.set(position); camera.update(); } // public Body createBox() { Vector2[] verticles = new Vector2[8]; verticles[0] = new Vector2(2f * 10 / utils.Constants.PPM, 2f * 10 / utils.Constants.PPM); verticles[1] = new Vector2(2f * 10 / utils.Constants.PPM, -2f * 10 / utils.Constants.PPM); verticles[2] = new Vector2(-2f * 10 / utils.Constants.PPM, 2f * 10 / utils.Constants.PPM); verticles[3] = new Vector2(-2f * 10 / utils.Constants.PPM, -2f * 10 / utils.Constants.PPM); verticles[4] = new Vector2(6f * 10 / utils.Constants.PPM, -2f * 10 / utils.Constants.PPM); verticles[5] = new Vector2(6f * 10 / utils.Constants.PPM, 0f * 10 / utils.Constants.PPM); verticles[6] = new Vector2(-1f * 10 / utils.Constants.PPM, -2f * 10 / utils.Constants.PPM); verticles[7] = new Vector2(4.5f * 10 / utils.Constants.PPM, -2f * 10 / utils.Constants.PPM); PolygonShape shape = new PolygonShape(); Body fBody; BodyDef def = new BodyDef(); def.type = BodyDef.BodyType.DynamicBody; def.position.set(0, 0); def.fixedRotation = false; fBody = world.createBody(def); shape.set(verticles); // FixtureDef fd = new FixtureDef(); // , fd.shape = shape; // fd.friction = 0.5f; // fd.density = 3f; // fd.restitution = 0.5f; fBody.createFixture(fd); fBody.createFixture(fd); shape.dispose(); return fBody; } // public Body createWeel(float xo, float yo) { CircleShape shape = new CircleShape(); Body fBody; BodyDef def = new BodyDef(); def.type = BodyDef.BodyType.DynamicBody; def.position.set(xo * 10 / utils.Constants.PPM, yo * 10 / utils.Constants.PPM); def.fixedRotation = false; fBody = world.createBody(def); shape.setRadius(2.0f * 10 / utils.Constants.PPM); // FixtureDef fd = new FixtureDef(); fd.shape = shape; fd.friction = 0.7f; fd.density = 3f; fd.restitution = 0.5f; fBody.createFixture(fd); shape.dispose(); return fBody; } // public Body createFloor() { Vector2[] verticles = new Vector2[4]; verticles[0] = new Vector2(-100f * 10 / utils.Constants.PPM, -2f * 10 / utils.Constants.PPM); verticles[1] = new Vector2(300f * 10 / utils.Constants.PPM, -2f * 10 / utils.Constants.PPM); verticles[2] = new Vector2(300f * 10 / utils.Constants.PPM, -5f * 10 / utils.Constants.PPM); verticles[3] = new Vector2(-100f * 10 / utils.Constants.PPM, -5f * 10 / utils.Constants.PPM); PolygonShape shape = new PolygonShape(); Body fBody; BodyDef def = new BodyDef(); def.type = BodyDef.BodyType.StaticBody; def.position.set(0, 0); def.fixedRotation = true; fBody = world.createBody(def); shape.set(verticles); FixtureDef fd = new FixtureDef(); fd.shape = shape; fd.friction = 0.5f; fd.density = 3f; fd.restitution = 0.5f; fBody.createFixture(fd); shape.dispose(); return fBody; } // ! public Body createTriangle(float xo, float x1, float x2, float yo, float y1, float y2) { Vector2[] verticles = new Vector2[3]; verticles[0] = new Vector2(xo * 10 / utils.Constants.PPM, yo * 10 / utils.Constants.PPM); verticles[1] = new Vector2(x1 * 10 / utils.Constants.PPM, y1 * 10 / utils.Constants.PPM); verticles[2] = new Vector2(x2 * 10 / utils.Constants.PPM, y2 * 10 / utils.Constants.PPM); PolygonShape shape = new PolygonShape(); Body fBody; BodyDef def = new BodyDef(); def.type = BodyDef.BodyType.StaticBody; def.position.set(0, 0); def.fixedRotation = true; fBody = world.createBody(def); shape.set(verticles); FixtureDef fd = new FixtureDef(); fd.shape = shape; fd.friction = 0.5f; fd.density = 10f; fd.restitution = 0f; fBody.createFixture(fd); shape.dispose(); return fBody; } } Figure 4. What do we get when compiling?
We create our car engine that turns its wheels. But it works forever, because there is no energy loss. So we create our perpetual motion machine!
And you wonder what is at the end of the level? Send screenshots in the comments as you pass. Thank you for reading the article to the end! I hope you can create your car in Box2D!
PS Waiting for your questions in the comments! Long live the game physics!
Source: https://habr.com/ru/post/450442/
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