Box2d Collision Detection with Arrays

Question

I'm developing in AndEngine I have nearly completed my game, but unfortunately, it suffers from a low fps occasionally due to the fact that I am checking .collideswith a lot in my update loop. I now understand that this is the problem, and I have been trying to change it using Box2d with bodies and such as in theory, this is exactly what I need, but I can't get a grasp around it!

Basically, I have 4 arrays; one for cars, three for enemies. Cars drive from left to right, and if they make contact with any of these enemies, it's speed changes depending. Do I have to allocate a body to each one of cars and enemies when I am loading their arrays? And then how do I check? do I run a for loop, and then an 'isBodyContacted(carBody, iceBergBody);' in the update look? It's a bit cofusing!

For reference, loading my car:

private void loadCar() {
            for (int i = 0; i < rManager.getInstance().carArray.length; i++) {
                    rManager.getInstance().carArray[i] = new Car(new Sprite(
                                    rManager.getInstance().spawnPoint[i].getSpawnPos().x,
                                    rManager.getInstance().spawnPoint[i].getSpawnPos().y,
                                    rManager.getInstance().car_region,
                                    engine.getVertexBufferObjectManager()) {
                            @Override
                            public boolean onAreaTouched(final TouchEvent pSceneTouchEvent,
                                            final float pTouchAreaLocalX,
                                            final float pTouchAreaLocalY) {

                                    if (pSceneTouchEvent.isActionMove()
                                                    && GameManager.getInstance().getDebugMode() == true) {
                                            this.setPosition(pSceneTouchEvent.getX(),
                                                            pSceneTouchEvent.getY());
                                    }
                                    return true;
                            }
                    });
            }

            for (int i = 0; i < rManager.getInstance().carArray.length; i++) {
                    rManager.getInstance().carArray[i].getCarSprite().setScale(0.5f);
                    rManager.getInstance().carArray[i].getCarSprite().setAnchorCenter(
                                    0, 0);
                    colourX = (randNumber(2, 9));
                    colourY = (randNumber(2, 9));
                    colourZ = (randNumber(2, 9));
                    colourX /= 10;
                    colourY /= 10;
                    colourZ /= 10;
                    rManager.getInstance().carArray[i].getCarSprite().setColor(colourZ,
                                    colourY, colourZ);
                    attachChild(rManager.getInstance().carArray[i].getCarSprite());
                    this.registerTouchArea(rManager.getInstance().carArray[i]
                                    .getCarSprite());
                    this.setTouchAreaBindingOnActionDownEnabled(true);
            }
    }

Loading an enemy..

void loadIceBerg() {
            for (int i = 0; i < rManager.getInstance().iceBergArray.length; i++) {
                    rManager.getInstance().iceBergArray[i] = new IceBergEnemy(
                                    new Sprite(randNumber(200, 700), randNumber(0, 480),
                                                    rManager.getInstance().iceBerg_region,
                                                    engine.getVertexBufferObjectManager()) {
                                            @Override
                                            public boolean onAreaTouched(final TouchEvent pSceneTouchEvent, final float pTouchAreaLocalX, final float pTouchAreaLocalY) {
                                                    this.setPosition(pSceneTouchEvent.getX(), pSceneTouchEvent.getY());
                                                    if (this.getY() > rManager.getInstance().camera.getHeight() - (this.getHeight() / 2) || this.getY() < 0 + (this.getHeight() / 2))
                                                    {
                                                            this.setPosition(200 - (pDifficultyLevel * 20),
                                                                            -100);
                                                                                                                            showScore(50, " ice berg!");
                                                            this.setVisible(false);

                                                    }      

                                                    if(pSceneTouchEvent.isActionUp())
                                                    {
                                                            updateScore(50);
                                                            GameManager.getInstance().updateTotalIceBergEnemiesKilled();

                                                    }



                                                    return true;
                                            }
                                    });

                    rManager.getInstance().iceBergArray[i].getIceBergSprite()
                                    .setPosition(
                                                    rManager.getInstance().iceBergArray[i]
                                                                    .getIceBergSprite().getX(),
                                                    rManager.getInstance().iceBergArray[i]
                                                                    .getIceBergSprite().getY());
                    rManager.getInstance().iceBergArray[i].getIceBergSprite().setScale(
                                    0.8f);
                    this.registerTouchArea(rManager.getInstance().iceBergArray[i]
                                    .getIceBergSprite());
                    this.setTouchAreaBindingOnActionDownEnabled(true);

                    attachChild(rManager.getInstance().iceBergArray[i]
                                    .getIceBergSprite());
            }
    }

Some collision!

else if (rManager.getInstance().iceBergArray[2]
                                                    .getIceBergSprite().collidesWith(
                                                                    rManager.getInstance().carArray[r]
                                                                                    .getCarSprite())) {
                                            rManager.getInstance().carArray[r].setCarSpeed(0f);
                                    }

                                    else if (rManager.getInstance().iceBergArray[3]
                                                    .getIceBergSprite().collidesWith(
                                                                    rManager.getInstance().carArray[r]
                                                                                    .getCarSprite())) {
                                            rManager.getInstance().carArray[r].setCarSpeed(0f);
                                    }

                                    else if (rManager.getInstance().iceBergArray[4]
                                                    .getIceBergSprite().collidesWith(
                                                                    rManager.getInstance().carArray[r]
                                                                                    .getCarSprite())) {
                                            rManager.getInstance().carArray[r].setCarSpeed(0f);
                                    }

                                    else if (rManager.getInstance().iceBergArray[5]
                                                    .getIceBergSprite().collidesWith(
                                                                    rManager.getInstance().carArray[r]
                                                                                    .getCarSprite())) {
                                            rManager.getInstance().carArray[r].setCarSpeed(0f);
                                    }

I have found many tutorials, but none seem to reference an array of objects, and that is exactly what I need. If someone could help me or provide some sort of quick tutorial, then that would be greatly appreciated. Thanks!!

Answer 1

You should not use any loops to check each possible combination of collision. Instead, you should register a listener for the whole World and set user data on your bodies (eg type = "car", "enemy"). Then in the listener, you just check which two objects collided. Check out this example:

http://www.andengine.org/forums/gles2/collision-events-t7140.html#p31300