Hi Everyone,

I'm having this weird issue with my code for projectile collisions in my 3D game.

My gun functions with casting a Ray and checking for collisions against Spheres around my objects , located in the appropriate Collision Tile, of my Uniform Grid Tile System.

Now everything works fin, but sometimes for a reason I can't figure out, my Ray Collides with spheres behind the character firing the gun. And so it screwes up everything, and since I have a sorting process right after collision detections that determines which collision happened first to determine which object takes the fire (because my projectile does not travel through objects) it makes it not work as it should.

Here is some code that shows you what going on.

DragonSC is a car object and here is the collision code that determines if the DragonSC's Collision Sphere, collides with the Ray being Casted.

x,y,z are the starting coordinates of my ray, starting at the Tip of the Fired Gun, xa, ya, za are the end coordinates of the ray (10000.0f further down the Line). Roty is the Angle the Firing character is facing and Rotx is the Angle at which the gun is firing, meaning at 90.0f the gun would be firing straight up in the air, parrallel to the Y axis.

Is there anything not right in my algorythm, I checked it 100 times using Sources on Stack Overflow and my Mathematics for 3D Game Programming & Computer Graphics Book by Eric Lengyel.

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Thanks

Thanks, it's a good Idea.

I thought about it and it would work, but it seems to be limited.

I mean, is this a common problem with ray casting or am I missing something here? Is the culling of spheres behind the character that is firing the ACTUAL thing that is missing?

I'm trying first to not have to do that.

You need to check the values of d and d2 (in your code) to use the smallest one, these are distance along the ray's direction to the intersection. If the smallest one is negative, there is no intersection since the sphere is behind.

Something like this (note line "if ( t1 < T(0) )"):

template < typename T >
Bool Ray3D<T>:: intersectsSphere( const Vector3D<T>& position, T radius, T& distance ) const
{
	Vector3D<T> d = position - origin;
	T dSquared = d.getMagnitudeSquared();
	T rSquared = radius*radius;
	
	if ( dSquared < rSquared )
	{
		// The ray starts inside the sphere and so there is an intersection.
		distance = T(0);
		return true;
	}
	else
	{
		// Find the closest point on the ray to the sphere's center.
		T t1 = math::dot( d, direction );
		
		if ( t1 < T(0) )
		{
			// The ray points away from the sphere so there is no intersection.
			return false;
		}
		
		// Find the distance from the closest point to the sphere's surface.
		T t2Squared = rSquared - dSquared + t1*t1;
		
		if ( t2Squared < T(0) )
			return false;
		
		// Compute the distance along the ray of the intersection.
		distance = t1 - math::sqrt(t2Squared);
		
		return true;
	}
}

Yessir, CCRicer , you are totally right, it at least improves performance.

And to answer your question, yes the ray will collide with object in front and behind, not only behind if the collision behind happens.

Aressera , Thank you very much for your great answer I did not know that. I will do that.

Ravyne, you're awesome.

All your answers together are helping me a great deal, thank you very much!

Peace my Matrix Brothers. :)

IT WORKS!!!!

WOUHOU ! you guys are the best in the universe.

Thank you!