/// <summary>
/// Build a rotation matrix from the specified axis/angle rotation.
/// </summary>
/// <param name="axis">The axis to rotate about.</param>
/// <param name="angle">Angle in radians to rotate counter-clockwise (looking in the direction of the given axis).</param>
/// <param name="result">A matrix instance.</param>
public static void CreateFromAxisAngle(Vector3F axis, float angle, out Matrix4F result)
{
float cos = (float)System.Math.Cos(-angle);
float sin = (float)System.Math.Sin(-angle);
float t = 1.0f - cos;
axis.Normalize();
result = new Matrix4F(t * axis.X * axis.X + cos, t * axis.X * axis.Y - sin * axis.Z, t * axis.X * axis.Z + sin * axis.Y, 0.0f,
t * axis.X * axis.Y + sin * axis.Z, t * axis.Y * axis.Y + cos, t * axis.Y * axis.Z - sin * axis.X, 0.0f,
t * axis.X * axis.Z - sin * axis.Y, t * axis.Y * axis.Z + sin * axis.X, t * axis.Z * axis.Z + cos, 0.0f,
0, 0, 0, 1);
}
/// <summary>
/// Build a world space to camera space matrix
/// </summary>
/// <param name="eye">Eye (camera) position in world space</param>
/// <param name="target">Target position in world space</param>
/// <param name="up">Up vector in world space (should not be parallel to the camera direction, that is target - eye)</param>
/// <returns>A Matrix4F that transforms world space to camera space</returns>
public static Matrix4F LookAt(Vector3F eye, Vector3F target, Vector3F up)
{
Vector3F z = Vector3F.Normalize(eye - target);
Vector3F x = Vector3F.Normalize(Vector3F.Cross(up, z));
Vector3F y = Vector3F.Normalize(Vector3F.Cross(z, x));
Matrix4F rot = new Matrix4F(new Vector4F(x.X, y.X, z.X, 0.0f),
new Vector4F(x.Y, y.Y, z.Y, 0.0f),
new Vector4F(x.Z, y.Z, z.Z, 0.0f),
Vector4F.UnitW);
Matrix4F trans = Matrix4F.CreateTranslation(eye * -1.0f);
return(trans * rot);
}
/// <summary>
/// Build a quaternion from the given axis and angle
/// </summary>
/// <param name="axis">The axis to rotate about</param>
/// <param name="angle">The rotation angle in radians</param>
/// <returns></returns>
public static Quaternion FromAxisAngle(Vector3F axis, float angle)
{
if (axis.LengthSquared == 0.0f)
{
return(Identity);
}
Quaternion result = Identity;
angle *= 0.5f;
axis.Normalize();
result.Xyz = axis * (float)System.Math.Sin(angle);
result.W = (float)System.Math.Cos(angle);
return(Normalize(result));
}
