[英]Why do i have to initialize the ball in Resize() method? - Libgdx
我正在制作一个简单的Bouncing Ball游戏,即使我通过BallScreen类的Show()方法中的BouncingBall类构造函数调用init()方法,也不会创建球。 因此,要创建一个球,我应该在Resize()方法中调用BouncingBall的init()方法。 为什么? 它不是应该在Show()方法中创建的吗?
这是弹跳球的代码
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);
}
}
这是弹跳球的屏幕类
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();
}
}
问题在这一行:
radius = RADIUS_RATIO * Math.min(viewport.getScreenWidth(), viewport.getScreenHeight());
当您创建FitViewPort
并传递给BouncingBall
时,此时的视口仅具有您设置的480的worldWidth和worldHeight。那时,视口的screenwidth和screenheight为零,因此您的半径初始化为零值。
但是在update()
方法之后,如果我调用init()
方法:
viewport.update(width,height,true); // this method set value to screenwidth/height
当您在视口的屏幕宽度和屏幕高度之后视视口调用更新方法时,根据您所使用的视口类型,视口的屏幕宽度和屏幕高度具有一定的值。
在update()
如果我调用ball.init(viewport);
则半径不是零值,以便在屏幕上可见球。
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