Fix calculation of closest point to origin on 2D segment in canonical box/cylinder intersection test.

Hi David, I noticed incorrect results when testing for box/cylinder intersection. I found a sign error in the code computing the squared distance of a 2D segment to the origin.

Here is a test program that gives an incorrect result before this fix and a correct result afterwards.

#include <Mathematics/IntrCanonicalBox3Cylinder3.h>

#include <iostream>

int main(int argc, char **argv) {

    gte::Line3<float> axis(
        gte::Vector3<float>({ -2.788151f, -2.091865f, 0.8015f }),
        gte::Vector3<float>({ 0.10444f, 0.328969f, 0.938548f })
    );

    gte::Cylinder3<float> cyl(axis, 0.39f, 2.1f);
    gte::CanonicalBox3<float> box(gte::Vector3<float>({ 2.5f, 2.5f, 1.35f }));

    gte::TIQuery<float, gte::CanonicalBox3<float>, gte::Cylinder3<float>> intersect_query;

    // Note that
    // * the origin of the cylinder lies less than 0.3 units from the -X side of the box
    // * the height of the cylinder exceeds the diameter of the cylinder, so the cylinder
    //   contains the sphere having the cylinder's diameter centred at the cylinder origin
    // so the cylinder and the box certainly collide.

    if (intersect_query(box, cyl).intersect) { std::cout << "PASS\n"; } else { std::cout << "FAIL\n"; }
}

davideberly / GeometricTools

Fix calculation of closest point to origin on 2D segment in canonical box/cylinder intersection test. #44