以相反的方式拍摄？- AndEngine经典教程

Question

好吧，这应该很简单，但我在数学上把自己给绊倒了。使用AndEngine BTW>

我正在使用一些教程……画面左边的英雄(风景)向右射击。一切都运行得很好。现在我想让英雄在屏幕的右边拍摄左边。我在原地打转，希望能得到一些帮助。这是我用来做左英雄，右射击的代码。

/** shoots a projectile from the player's position along the touched area */
private void shootProjectile(final float pX, final float pY) {

    int offX = (int) (pX - (hero.getX()));
    int offY = (int) (pY - (hero.getY() + hero.getHeight()/2));
    if (offX <= 0) return;

    // position the projectile on the player and set up path
    projectile = pPool.obtainPoolItem();

    int realX = (int) (mCamera.getWidth() - (hero.getX()  ) );
    float ratio = (float) realX / (float) offX;
    int realY = (int) ((offY * ratio));

    float length = (float) Math.sqrt((realX * realX) + (realY * realY));
    float velocity = 280.0f / .5f; // 480 pixels per (sec)f on screen
    float realMoveDuration = length / velocity;

    // defining a moveBymodifier from the projectile's position to the
    // calculated one

    //this code angles the projectile sprite
    double PI = 3.14159265;
    float  dx = pX -  hero.getX();
    float  dy = pY -  hero.getY()-50;

    double  Radius = Math.atan2(dy,dx);
    double Angle = Radius * 180 / PI;

    projectile.setRotation((float)Angle); // sets the angle of the projectile

    //Move modifier for projectile
    MoveByModifier movMByod = new MoveByModifier(realMoveDuration, realX, realY);

    final ParallelEntityModifier par = new ParallelEntityModifier(movMByod);

    DelayModifier dMod = new DelayModifier(0.001f);
    dMod.addModifierListener(new IModifierListener<IEntity>() {

        @Override
        public void onModifierStarted(IModifier<IEntity> arg0, IEntity arg1) {
        }

        @Override
        public void onModifierFinished(IModifier<IEntity> arg0, IEntity arg1) {
            // TODO Auto-generated method stub
            shootingSound.play();
            projectile.setVisible(true);
            projectile.setPosition(hero.getX(), hero.getY() + hero.getHeight() / 2);
            projectilesToBeAdded.add(projectile);
            projectile.animate(50);

        }
    });

    SequenceEntityModifier seq = new SequenceEntityModifier(dMod, par);
    projectile.registerEntityModifier(seq);
    projectile.setVisible(false);
    mMainScene.attachChild(projectile, 1);

我已经把英雄放在右边了。我需要做什么才能让投射物正确地向左移动？

非常感谢你的帮助。

MWM

Answer 1

您不应该以这种方式使用DelayModifier。相反，为您的精灵创建PhysicsHandler，然后将速度设置为PhysicsHandler。类似于：

PhysicsHandler phys = new PhysicsHandler();
projectile.registerUpdateHandler(phys);
phys.setVelocityX(50);

这将负责移动你的弹丸。你也可以用同样的方法在物理处理器上设置加速。因此，如果你将初始速度设置为向上和向左，然后将加速度设置为向下，射弹将首先向左和向上飞行，然后逐渐下降。而且你不需要自己做任何计算。

Answer 2

此代码与http://jimmaru.wordpress.com/2011/09/28/andengine-simple-android-game-tutorial/中的代码类似。如果是，请尝试以下代码：

private void shootProjectile(final float pX, final float pY) {
    int side = 1;
    int offX = (int) (pX - (hero.getX()));
    int offY = (int) (pY - (hero.getY() + hero.getHeight()/2));
    if (offX <= 0){
       side=-1
    }

    // position the projectile on the player and set up path
    projectile = pPool.obtainPoolItem();

    int realX = (int) (mCamera.getWidth() - (hero.getX()  ) ) * side;
    ....

我在link的代码中遇到了同样的问题，有了这个改变，我可以在屏幕中间用一个球员在两边投篮。