Hi All,

I'm doing space invadres clone game, and when I tried to record the game using camcoder, the collision detection between bullets and the invaders are droped and it's not behaving correctly i.e some bullets can hit invaders that shouldn't be hit, because there are in-front other invaders.

The collision detection is here:

void CheckBulletsInvadersCollision(Ship *ship)
{
	for (vector<Invader*>::iterator invIter = g_Invaders.invaders->begin(); invIter != g_Invaders.invaders->end();)
	{
		if ((*invIter)->Alive)
		{
			bool isBulletsInvaderCollided = false;

			for (list<Bullet*>::iterator it = ship->Bullets->begin(); it != ship->Bullets->end();)
			{

				float left = (*it)->Position.x - 5;
				float top = (*it)->Position.y - 13;

				if (CheckCollision(left, top, (*invIter)->AlienSprite->m_X, (*invIter)->AlienSprite->GetImage()->GetWidth() / 4
					, (*invIter)->AlienSprite->m_Y, (*invIter)->AlienSprite->GetImage()->GetHeight() / 4))
				{
				 	isBulletsInvaderCollided = true;
  					Bullet *bullet = *it;
					it = ship->Bullets->erase(it);
					delete bullet;

					ship->Canfire = true;
				}
				else
				{
					it++;
				}

			}
			if (isBulletsInvaderCollided)
			{
				Invader *inv = *invIter;
				g_Invaders.invaders->erase(invIter);
				delete inv;
				g_Invaders.killed++;
				g_Invaders.alive = false;
			}
			else
			{
				invIter++;
			}
		}
	}
}

Is CheckCollision a sweeping algorithm, or a static intersection test?

Do you have a fixed time step?

It is generally best to have a fixed time step to avoid bugs related to faster computers, slower computers, and bogged down computers. That may be your problem. It is also generally a good idea to use a swept volume collision test to scan for collisions over the entire time between frames. Otherwise it is possible for fast moving objects to hop over each other, for players to hide inside walls, and other trickery.

The collision is a simple intersection test.

That is my game loop looks like:

uint32 timer = (uint32)s3eTimerGetMs();
 	// Loop forever, until the user or the OS performs some action to quit the app
	while (!s3eDeviceCheckQuitRequest())
	{
		// Calculate the amount of time that's passed since last frame
		int delta = uint32(s3eTimerGetMs()) - timer;
		timer += delta;

		g_Input.Update();

		Iw2DSurfaceClear(0x00000000);

		Move_Invaders(delta);

		ship->Update(delta);
		ship->Render();

		if (ship->NumFire == 9)
		{
			ship->NumFire = 0;
			saucer.mAlive = true;
		}
		saucer.Update(delta);
		saucer.Render();

		Render_Barriers(barriers);

		CheckBulletsSaucerCollision(&saucer, ship);
		CheckBulletsInvadersCollision(ship);
		CheckBulletsBarriersCollision(ship, barriers, gameResources);
		 
		//Iw2DDrawString("Score = ", CIwFVec2(10, 10), CIwFVec2(50, 50), IW_2D_FONT_ALIGN_CENTRE, IW_2D_FONT_ALIGN_CENTRE);
        //Draws Surface to screen
        Iw2DSurfaceShow();

        // Sleep for 0ms to allow the OS to process events etc.
        s3eDeviceYield(0);
    }