Java 按下移动键时，将精灵保持在屏幕上

按下按键时，如何确保

太空飞船精灵

保持在屏幕上。我不想让宇宙飞船离开屏幕

public void render() {      
    if(Gdx.input.isKeyPressed(Keys.DPAD_LEFT)) 
      movex -= Gdx.graphics.getDeltaTime() *speed;
    if(Gdx.input.isKeyPressed(Keys.DPAD_RIGHT)) 
      movex += Gdx.graphics.getDeltaTime() * speed;
    if(Gdx.input.isKeyPressed(Keys.DPAD_UP)) 
      moveY += Gdx.graphics.getDeltaTime() * speed;  
    if(Gdx.input.isKeyPressed(Keys.DPAD_DOWN)) 
      moveY -= Gdx.graphics.getDeltaTime() * speed;
    Gdx.gl.glClearColor(0,0,0,0);
    Gdx.gl.glClear(GL10.GL_COLOR_BUFFER_BIT);
    Gdx.gl.glViewport(0, 0, Gdx.graphics.getWidth(), Gdx.graphics.getHeight());

    batch.setProjectionMatrix(camera.combined);
    batch.begin();
    //sprite.draw(batch);
    batch.draw(background, 0, 0);
    batch.draw(spaceshipSprite, movex, moveY );
    //spaceshipSprite.draw(batch);
    batch.end();
}

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移动相机而不是精灵，或与精灵一起移动。在相机上使用

translate

方法。看