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Line - Sphere Intersection Code Not Working (VB6)

Started by Kustaz May 27, 2006 at 9:57 PM 0 replies 500+ views

Original Post

May 27, 2006 at 9:57 PM

Hi there I adapted the following piece of code from information I gathered off the internet. It appeared to work, until I started using it extensively. It returns a collision no matter where I point my line, unless I point it in the opposite direction (Eg. Negative Z axis). Here is the code below:




Public Function Primitive_Intersect(R As Ray, ByRef Dist As Double) As Integer

Dim V As New Vector3
V.VAssignV VectorMath.VSubtract(R.Origin, Me.Origin)

Dim B As Double
B = VectorMath.VDotProduct(V, R.Direction) * -1

Dim Det As Double
Det = (B * B) - VectorMath.VDotProduct(V, V) + (Me.Radius * Me.Radius)

Primitive_Intersect = RAY_MISS

    If (Det > 0) Then

        Det = Sqr(Det)

        Dim i1 As Double
        i1 = B - Det

        Dim i2 As Double
        i2 = B + Det

            If (i2 > 0) Then
            
                If (i1 < 0) Then
        
                    If (i2 < Dist) Then
      
                        Dist = i2
                        Primitive_Intersect = RAY_INSIDE
   
                    End If
                 
                Else
         
                If (i1 < Dist) Then
        
                    Dist = i1
                    Primitive_Intersect = RAY_HIT
     
                End If
   
            End If
            
        End If
 
    End If


End Function

Now, all my vector functions work. I have used the extensively as well, but with no problems. The values I am testing this function with are: the Ray: R.Direction = (-400, -300, 2) R.Origin = (0,0,0) Dist = 80 The Sphere: Me.Origin = (0, 0, 5) Me.Radius = 3 Even if you think there is nothing wrong with it, please tell me so. I've been trying to get this to work for some time.

tthibault

May 29, 2006 at 11:15 PM

Quake3

/*================RaySphereIntersections================*/int RaySphereIntersections( vec3_t origin, float radius, vec3_t point, vec3_t dir, vec3_t intersections[2] ) {	float b, c, d, t;	//	| origin - (point + t * dir) | = radius	//	a = dir[0]^2 + dir[1]^2 + dir[2]^2;	//	b = 2 * (dir[0] * (point[0] - origin[0]) + dir[1] * (point[1] - origin[1]) + dir[2] * (point[2] - origin[2]));	//	c = (point[0] - origin[0])^2 + (point[1] - origin[1])^2 + (point[2] - origin[2])^2 - radius^2;	// normalize dir so a = 1	VectorNormalize(dir);	b = 2 * (dir[0] * (point[0] - origin[0]) + dir[1] * (point[1] - origin[1]) + dir[2] * (point[2] - origin[2]));	c = (point[0] - origin[0]) * (point[0] - origin[0]) +		(point[1] - origin[1]) * (point[1] - origin[1]) +		(point[2] - origin[2]) * (point[2] - origin[2]) -		radius * radius;	d = b * b - 4 * c;	if (d > 0) {		t = (- b + sqrt(d)) / 2;		VectorMA(point, t, dir, intersections[0]);		t = (- b - sqrt(d)) / 2;		VectorMA(point, t, dir, intersections[1]);		return 2;	}	else if (d == 0) {		t = (- b ) / 2;		VectorMA(point, t, dir, intersections[0]);		return 1;	}	return 0;}

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