Blendfunc has overhead?

cocos2d-x C++
1

I’m make painting application.

painting some colors are fine but eraser has some problems.

here is my code,

void HelloWorld::onTouchesMoved(const std::vector<Touch*>&touches, Event* unused_event)
{
pRTex->begin();
	float distance = start.getDistance(end);
	if (distance > 1)
	{
		int d = (int)distance;
		_erasers.clear();
		for(int i = 0; i < d; ++i)
		{
			DrawNode* node = DrawNode::create();
			if(modeBit==2)
				node->drawDot(Vec2(),eraser_size,Color4F(0,0,0,0));
			else
				node->drawDot(Vec2(),eraser_size,Color4F::BLACK);
			_erasers.pushBack(node);
		}
		for (int i = 0; i < d; i++)
		{
			float difx = end.x - start.x;
			float dify = end.y - start.y;
			float delta = (float)i / distance;
			_erasers.at(i)->setPosition(Vec2(start.x + (difx * delta), start.y + (dify * delta)));
			_erasers.at(i)->setRotation(rand() % 360);
			float r = (float)(rand() % 50 / 50.f) + 0.25f;
			_erasers.at(i)->setScale(r);
			if(modeBit==2)
				_erasers.at(i)->setBlendFunc(blendFunc);
			_erasers.at(i)->visit();
		}
	}
	pRTex->end();
}

this eraser function has overhead that application slowed and stopped.

I’m sorry for proper english.

please help, Thanks