Question

我正在尝试用libgdx中的box2d制作样本。

我希望球在box2d世界中随着重力而下降。现在它下降但没有加速（我看到球在加速度= 0时下降）。我试图添加阻尼，密度......但没有变化。请帮我找到我的错。非常感谢你。
这是此问题的视频：youtube.com/watch?v=NkbcVMsB2S0
;在此视频中，您可以看到圆圈在加速度= 0时下降。我试图改变一些参数，但看起来加速度始终为零。这是一个简单的课程：

public class MyGdxGame implements ApplicationListener, InputProcessor {
World world;
Box2DDebugRenderer debugRenderer;
OrthographicCamera camera;
static final float BOX_STEP = 1 / 45f;
static final int BOX_VELOCITY_ITERATIONS = 6;
static final int BOX_POSITION_ITERATIONS = 2;
static final float WORLD_TO_BOX = 0.01f;
static final float BOX_WORLD_TO = 100f;

private int counter = 100;
private Body body;

@Override
public void create() {
    world = new World(new Vector2(0, -200f), false);
    world.setContinuousPhysics(true);
    camera = new OrthographicCamera();
    camera.viewportHeight = 320;
    camera.viewportWidth = 480;
    camera.position.set(camera.viewportWidth * .5f,
            camera.viewportHeight * .5f, 0f);
    camera.update();
    // Ground body
    BodyDef groundBodyDef = new BodyDef();
    groundBodyDef.position.set(new Vector2(0, 10));
    Body groundBody = world.createBody(groundBodyDef);
    PolygonShape groundBox = new PolygonShape();
    groundBody.createFixture(groundBox, 0.0f);
    // Dynamic Body
    BodyDef bodyDef = new BodyDef();
    bodyDef.type = BodyType.DynamicBody;
    bodyDef.position.set(camera.viewportWidth / 2, camera.viewportHeight);
    bodyDef.angularDamping = 0.01f;
    bodyDef.linearDamping = 0.0f;
    body = world.createBody(bodyDef);
    CircleShape dynamicCircle = new CircleShape();
    dynamicCircle.setRadius(10f);
    FixtureDef fixtureDef = new FixtureDef();
    fixtureDef.shape = dynamicCircle;
    fixtureDef.density = 10.0f;
    fixtureDef.friction = 0.0f;
    fixtureDef.restitution = 0f;
    body.createFixture(fixtureDef);
    MassData massData = new MassData();
    massData.mass = 50f;
    body.setMassData(massData);
    body.setGravityScale(1f);
    debugRenderer = new Box2DDebugRenderer();
    Gdx.input.setInputProcessor(this);
}

@Override
public void dispose() {
}

@Override
public void render() {
    Gdx.gl.glClear(GL10.GL_COLOR_BUFFER_BIT);

    if (counter < 10) {
        body.applyForceToCenter(0, 200000f, true);
    }
    counter++;
    debugRenderer.render(world, camera.combined);
    world.step(BOX_STEP, BOX_VELOCITY_ITERATIONS, BOX_POSITION_ITERATIONS);
}

@Override
public void resize(int width, int height) {
}

@Override
public void pause() {
}

@Override
public void resume() {
}

@Override
public boolean keyDown(int keycode) {
    // TODO Auto-generated method stub
    return false;
}

@Override
public boolean keyUp(int keycode) {
    // TODO Auto-generated method stub
    return false;
}

@Override
public boolean keyTyped(char character) {
    // TODO Auto-generated method stub
    return false;
}

@Override
public boolean touchDown(int screenX, int screenY, int pointer, int button) {
    counter = 0;
    return false;
}

@Override
public boolean touchUp(int screenX, int screenY, int pointer, int button) {
    return false;
}

@Override
public boolean touchDragged(int screenX, int screenY, int pointer) {
    // TODO Auto-generated method stub
    return false;
}

@Override
public boolean mouseMoved(int screenX, int screenY) {
    // TODO Auto-generated method stub
    return false;
}

@Override
public boolean scrolled(int amount) {
    // TODO Auto-generated method stub
    return false;
}

Answer 1

我认为这是因为身体瞬间处于最大速度（因为重力非常高）。 Box2D有最大速度，我认为每步2米。您似乎是在移动设备上运行它，通常限制为60FPS。这意味着您每秒最多可以执行60次更新步骤，最大速度/速度为120m / s。顺便说一句，您的更新速率取决于帧速率。

我看到你已经定义了米到像素和像素到米的常数，但你没有在代码中的任何地方使用它们。这意味着你使用1：1的米到像素比率，因此任何身体可以拥有的最大速度是120px / s。这不是很多，从视频判断它可能是正确的。

常见的诀窍是缩小相机的视口，而不是缩放所有与box2d相关的内容。像这样：

camera.viewportHeight = Gdx.graphics.getHeight() * WORLD_TO_BOX;
camera.viewportWidth = Gdx.graphics.getWidth() * WORLD_TO_BOX;

Answer 2

我有同样的问题。在我的情况下，解决方案是将BOX_STEP参数的值更改为1/240（以前为1/60，然后最大线速度为120）

static final float BOX_STEP=1/240f;
static final int BOX_VELOCITY_ITERATIONS=20;
static final int BOX_POSITION_ITERATIONS=3;

所以在渲染器（）步骤中现在采用上面的

world.step(BOX_STEP, BOX_VELOCITY_ITERATIONS, BOX_POSITION_ITERATIONS);

我还介绍了noone answear，但没有改变步骤方法它没有工作

在box2d libgdx中缺少重力

2 个答案: