Question

我正在制作一个简单的Bouncing Ball游戏，即使我在BallScreen类的Show（）方法中通过BouncingBall类构造函数调用init（）方法，也不会创建球。所以要创建一个球，我应该在Resize（）方法中调用BouncingBall的init（）方法。为什么？是不是应该在Show（）方法中创建？

以下是Bouncing Ball的代码

public class BouncingBall {

public static final float RADIUS_RATIO = 0.04f;
public static final float START_KICK = 500.0f;
private static final float KICK_INTERVAL = 3f;
private static final float DRAG = 1f;


private Vector2 position;
private Vector2 velocity;
float radius;
float lastKick;

public BouncingBall(Viewport viewport) {
    init(viewport);
}

public void init(Viewport viewport) {
    position = new Vector2();
    position.x = viewport.getWorldWidth() / 2;
    position.y = viewport.getWorldHeight() / 2;

    velocity = new Vector2(0,0);

    radius = RADIUS_RATIO * Math.min(viewport.getScreenWidth(), viewport.getScreenHeight());
    startKick();
}

public void update(float delta, Viewport viewport) {

    float elapsedSeconds = MathUtils.nanoToSec * (TimeUtils.nanoTime() - lastKick);

    if (elapsedSeconds > KICK_INTERVAL) {
        lastKick = TimeUtils.nanoTime();
        startKick();
    }

    velocity.x -= delta * DRAG * velocity.x;
    velocity.y -= delta * DRAG * velocity.y;

    position.x += velocity.x * delta;
    position.y += velocity.y * delta;
    collision(radius,viewport);
}


public void collision(float radius, Viewport viewport) {
    if (position.x + radius > viewport.getWorldWidth()) {
        position.x = viewport.getWorldWidth() - radius;
        velocity.x = -velocity.x;
    }

    if (position.x - radius < 0) {
        position.x = radius;
        velocity.x = -velocity.x;
    }

    if (position.y + radius > viewport.getScreenHeight()) {
        position.y = viewport.getWorldHeight() - radius;
        velocity.y = -velocity.y;
    }

    if (position.y - radius < 0) {
        position.y = radius;
        velocity.y = -velocity.y;
    }
}

public void startKick() {
    Random random = new Random();
    float angle = random.nextFloat() * MathUtils.PI2;
    velocity.x = START_KICK * MathUtils.cos(angle);
    velocity.y = START_KICK * MathUtils.sin(angle);
}

public void render(ShapeRenderer renderer) {
    renderer.setColor(Color.RED);
    renderer.circle(position.x, position.y, radius);
}
}

这是Bouncing Ball的屏幕类

public class BallScreen extends ScreenAdapter {


private static final float WORLD_SIZE = 480f;
private static final String TAG = BallScreen.class.getSimpleName();

private BouncingBall ball;
private Viewport viewport;
private ShapeRenderer renderer;


@Override
public void show() {
    Gdx.app.log(TAG, "Show");
    viewport = new FitViewport(WORLD_SIZE, WORLD_SIZE);
    renderer = new ShapeRenderer();
    ball = new BouncingBall(viewport);
}

@Override
public void resize(int width, int height) {
    Gdx.app.log(TAG, "resize" + width + " " + height);
    viewport.update(width,height,true);
    ball.init(viewport);
}

@Override
public void dispose() {
    Gdx.app.log(TAG, "dispose");
    renderer.dispose();
}

@Override
public void render(float delta) {
    viewport.apply();
    Gdx.gl.glClearColor(0, 0, 0, 1);
    Gdx.gl20.glClear(GL20.GL_COLOR_BUFFER_BIT);

    renderer.setProjectionMatrix(viewport.getCamera().combined);
    renderer.begin(ShapeType.Filled);

    ball.update(delta, viewport);
    ball.render(renderer);

    renderer.end();

}
}

Answer 1

问题出在这一行：

radius = RADIUS_RATIO * Math.min(viewport.getScreenWidth(), viewport.getScreenHeight());

当你创建FitViewPort并传递给BouncingBall时，那时视口只有你设置的worldWidth和worldHeight 480.那时视口的screenwidth和screenheight为零，所以你的半径初始化没有价值。

但如果我调用update()方法，请init()方法之后：

viewport.update(width,height,true);  // this method set value to screenwidth/height

根据您正在使用的ViewPort类型，在视口的screenwidth和screenheight之后调用viewport上的update方法。

update()之后如果我拨打ball.init(viewport);，则半径不是零值，以便在屏幕上显示球。

为什么我必须在Resize（）方法中初始化球？ - Libgdx

1 个答案: