gistfile1.txt

{
    auto listener = larme::eventlistener::EventListenerTouchAction::create();
    listener->onTouchesActionZoom = [this](float distance) {
        this->cameraZoom += distance / 1000.0f;
        // ここで distanceのmaxを設定したほうがいいかも・
    };
    listener->onTouchesActionPan = [this](Vec2 distance) {
        this->cameraPosition -= distance / this->cameraZoom;
    };
    this->getEventDispatcher()->addEventListenerWithSceneGraphPriority(listener, this);
    this->setCameraMask((unsigned short)cocos2d::CameraFlag::USER2, true);
}

void LayerUsagi::update(float delta) {
    // カメラの設定
    auto size = Director::getInstance()->getVisibleSize();
    if (cameraZoom < 0.5f) {
        cameraZoom = 0.5f;
    } else if (1.5f < cameraZoom) {
        cameraZoom = 1.5f;
    }
    Vec2 zoomOffset = Vec2::ZERO;
    // 謎の式だがこれでおおよそ上手く動作する
    zoomOffset -= (1 - cameraZoom)/2 * Vec2(size.width, size.height);
    zoomOffset *= 1 / cameraZoom;
    camera->setPosition(cameraPosition + zoomOffset);
    camera->initOrthographic(size.width / cameraZoom, size.height / cameraZoom, -1, 1);
}

cameraZoom = min(1.5f, max(0.5f, cameraZoom)); // 0.5 ~ 1.5 の間に収める