//Derivative at point t
public float ExactDerivative(float t)
{
MyVector3 A = posA;
MyVector3 B = handle;
MyVector3 C = posB;
//Layer 1
//(1-t)A + tB = A - At + Bt
//(1-t)B + tC = B - Bt + Ct
//Layer 2
//(1-t)(A - At + Bt) + t(B - Bt + Ct)
//A - At + Bt - At + At^2 - Bt^2 + Bt - Bt^2 + Ct^2
//A - 2At + 2Bt + At^2 - 2Bt^2 + Ct^2
//A - t(2(A - B)) + t^2(A - 2B + C)
//Derivative: -(2(A - B)) + t(2(A - 2B + C))
MyVector3 derivativeVector = t * (2f * (A - 2f * B + C));
derivativeVector += -2f * (A - B);
float derivative = MyVector3.Magnitude(derivativeVector);
return(derivative);
}
//
// Derivative
//
public override float GetDerivative(float t)
{
MyVector3 derivativeVec = GetDerivativeVec(posA, posB, handleA, handleB, t);
float derivative = MyVector3.Magnitude(derivativeVec);
return(derivative);
}
//
// Calculate the area of a triangle in 3d space
//
//https://math.stackexchange.com/questions/128991/how-to-calculate-the-area-of-a-3d-triangle
public static float CalculateTriangleArea(MyVector3 p1, MyVector3 p2, MyVector3 p3)
{
MyVector3 normal = CalculateTriangleNormal(p1, p2, p3, shouldNormalize: false);
float parallelogramArea = MyVector3.Magnitude(normal);
float triangleArea = parallelogramArea * 0.5f;
return(triangleArea);
}
//
// Derivative at point t
//
public override float GetDerivative(float t)
{
//Alternative 1. Estimated
//float derivative = InterpolationHelpMethods.EstimateDerivative(this, t);
//Alternative 2. Exact
MyVector3 derivativeVec = GetDerivativeVec(posA, posB, handlePos, t);
float derivative = MyVector3.Magnitude(derivativeVec);
return(derivative);
}
//
// Alternative 3. Rotation Minimising Frame (also known as "Parallel Transport Frame" or "Bishop Frame")
//
//Gets its stability by incrementally rotating a coordinate system (= frame) as it is translate along the curve
//Has to be computed for the entire curve because we need the previous frame (previousTransform) belonging to a point before this point
//Is initalized by using "Fixed Up" or "Frenet Normal"
public static MyQuaternion GetOrientation_RotationFrame(MyVector3 position, MyVector3 tangent, InterpolationTransform previousTransform)
{
/*
* //This version is from https://pomax.github.io/bezierinfo/#pointvectors3d
* //Reflect the known frame onto the next point, by treating the plane through the curve at the point exactly between the next and previous points as a "mirror"
* MyVector3 v1 = position - previousTransform.position;
*
* float c1 = MyVector3.Dot(v1, v1);
*
* MyVector3 riL = previousTransform.Right - v1 * (2f / c1) * MyVector3.Dot(v1, previousTransform.Right);
*
* MyVector3 tiL = previousTransform.Forward - v1 * (2f / c1) * MyVector3.Dot(v1, previousTransform.Forward);
*
* //This gives the next point a tangent vector that's essentially pointing in the opposite direction of what it should be, and a normal that's slightly off-kilter
* //reflect the vectors of our "mirrored frame" a second time, but this time using the plane through the "next point" itself as "mirror".
* MyVector3 v2 = tangent - tiL;
*
* float c2 = MyVector3.Dot(v2, v2);
*
* //Now we can calculate the normal and right vector belonging to this orientation
* MyVector3 right = riL - v2 * (2f / c2) * MyVector3.Dot(v2, riL);
*
* //The source has right x tangent, but then every second normal is flipped
* MyVector3 normal = MyVector3.Cross(tangent, right);
*
* MyQuaternion orientation = new MyQuaternion(tangent, normal);
*/
//This version is from Game Programming Gems 2: The Parallel Transport Frame
//They generate the same result and this one is easier to understand
//The two tangents
MyVector3 T1 = previousTransform.Forward;
MyVector3 T2 = tangent;
//You move T1 to the new position, so A is a vector going from the new position
MyVector3 A = MyVector3.Cross(T1, T2);
//This is the angle between T1 and T2
float alpha = Mathf.Acos(MyVector3.Dot(T1, T2) / (MyVector3.Magnitude(T1) * MyVector3.Magnitude(T2)));
//Now rotate the previous frame around axis A with angle alpha
MyQuaternion F1 = previousTransform.orientation;
MyQuaternion F2 = MyQuaternion.RotateQuaternion(F1, alpha * Mathf.Rad2Deg, A);
MyQuaternion orientation = F2;
return(orientation);
}
//
// Estimate the derivative at point t
//
//https://www.youtube.com/watch?v=pHMzNW8Agq4
public static float EstimateDerivative(Curve curve, float t)
{
//We can estimate the derivative by taking a step in each direction of the point we are interested in
//Should be around this number
float derivativeStepSize = 0.0001f;
MyVector3 valueMinus = curve.GetInterpolatedValue(t - derivativeStepSize);
MyVector3 valuePlus = curve.GetInterpolatedValue(t + derivativeStepSize);
//Have to multiply by two because we are taking a step in each direction
MyVector3 derivativeVector = (valuePlus - valueMinus) * (1f / (derivativeStepSize * 2f));
float derivative = MyVector3.Magnitude(derivativeVector);
return(derivative);
}
//
// Calculate the center of circle in 3d space given three coordinates
//
//From https://gamedev.stackexchange.com/questions/60630/how-do-i-find-the-circumcenter-of-a-triangle-in-3d
public static MyVector3 CalculateCircleCenter(MyVector3 a, MyVector3 b, MyVector3 c)
{
MyVector3 ac = c - a;
MyVector3 ab = b - a;
MyVector3 abXac = MyVector3.Cross(ab, ac);
//This is the vector from a to the circumsphere center
MyVector3 toCircumsphereCenter = MyVector3.Cross(abXac, ab) * Mathf.Pow(MyVector3.Magnitude(ac), 2f);
toCircumsphereCenter += MyVector3.Cross(ac, abXac) * Mathf.Pow(MyVector3.Magnitude(ab), 2f);
toCircumsphereCenter *= (1f / (2f * Mathf.Pow(MyVector3.Magnitude(abXac), 2f)));
float circumsphereRadius = MyVector3.Magnitude(toCircumsphereCenter);
//The circumsphere center becomes
MyVector3 ccs = a + toCircumsphereCenter;
return(ccs);
}
//Actual derivative at point t
public float ExactDerivative(float t)
{
MyVector3 A = posA;
MyVector3 B = handleA;
MyVector3 C = handleB;
MyVector3 D = posB;
//Layer 1
//(1-t)A + tB = A - At + Bt
//(1-t)B + tC = B - Bt + Ct
//(1-t)C + tD = C - Ct + Dt
//Layer 2
//(1-t)(A - At + Bt) + t(B - Bt + Ct) = A - At + Bt - At + At^2 - Bt^2 + Bt - Bt^2 + Ct^2 = A - 2At + 2Bt + At^2 - 2Bt^2 + Ct^2
//(1-t)(B - Bt + Ct) + t(C - Ct + Dt) = B - Bt + Ct - Bt + Bt^2 - Ct^2 + Ct - Ct^2 + Dt^2 = B - 2Bt + 2Ct + Bt^2 - 2Ct^2 + Dt^2
//Layer 3
//(1-t)(A - 2At + 2Bt + At^2 - 2Bt^2 + Ct^2) + t(B - 2Bt + 2Ct + Bt^2 - 2Ct^2 + Dt^2)
//A - 2At + 2Bt + At^2 - 2Bt^2 + Ct^2 - At + 2At^2 - 2Bt^2 - At^3 + 2Bt^3 - Ct^3 + Bt - 2Bt^2 + 2Ct^2 + Bt^3 - 2Ct^3 + Dt^3
//A - 3At + 3Bt + 3At^2 - 6Bt^2 + 3Ct^2 - At^3 + 3Bt^3 - 3Ct^3 + Dt^3
//A - 3t(A - B) + t^2(3A - 6B + 3C) + t^3(-A + 3B - 3C + D)
//A - 3t(A - B) + t^2(3(A - 2B + C)) + t^3(-(A - 3(B - C) - D)
//The derivative: -3(A - B) + 2t(3(A - 2B + C)) + 3t^2(-(A - 3(B - C) - D)
//-3(A - B) + t(6(A - 2B + C)) + t^2(-3(A - 3(B - C) - D)
MyVector3 derivativeVector = t * t * (-3f * (A - 3f * (B - C) - D));
derivativeVector += t * (6f * (A - 2f * B + C));
derivativeVector += -3f * (A - B);
float derivative = MyVector3.Magnitude(derivativeVector);
return(derivative);
}
