triangle.cpp

#include "header/triangle.h"

triangle::triangle(const point3& a, const point3& b, const point3& c, const rayTracingMaterial& mat)
: object(mat){
    vertices[0] = a;
    vertices[1] = b;
    vertices[2] = c;
    normal = (b - a).cross(c - a).unit_vector();
}

// In this function we assume that the triangle coordinate are stored as ABC, and the hit point is D
hitInfo triangle::hit(const ray& r) const {

    hitInfo hit;

    double divisor = normal.unit_vector().dot(r.direction.unit_vector());

    if (divisor != 0) {

        double d = normal.dot(vertices[0]);
        double dividend = d - normal.dot(r.origin);

        double distance = dividend/divisor;

        if (distance > 0) {

            point3 hitPlan = r.at(distance);

            if (isPointInTriangle(hitPlan)) {

                hit.didHit = true;
                hit.distance = distance;
                hit.hitPoint = hitPlan;
                hit.normal = normal.unit_vector();

            }
        }
    }

    return hit;
}

double triangle::triangleArea(const point3& a, const point3& b, const point3& c) {
    point3 AB = b - a;
    point3 AC = c - a;

    return AB.cross(AC).length() / 2;
}

bool triangle::isPointInTriangle(const point3& point) const {
    double totalArea = triangleArea(vertices[0], vertices[1], vertices[2]);
    double area1 = triangleArea(point, vertices[0], vertices[1]);
    double area2 = triangleArea(point, vertices[1], vertices[2]);
    double area3 = triangleArea(point, vertices[2], vertices[0]);

    return fabs(totalArea - (area1 + area2 + area3)) < 1e-6;
}