Class AccretionDisk

examples/pde/bhrt.cpp:788–845

};

struct AccretionDisk : public Object {
    af::array disk_color;
    af::array center;
    af::array normal;
    double inner_radius;
    double outter_radius;

    AccretionDisk(const af::array& center, const af::array& normal,
                  double inner_radius, double outter_radius)
        : disk_color(af::array(3, {209.f, 77.f, 0.f}))
        , center(center)
        , normal(normal)
        , inner_radius(inner_radius)
        , outter_radius(outter_radius) {
        // disk_color = af::array(3, {254.f, 168.f, 29.f});
    }

    std::pair<HasHit, HitPos> intersect(
        const af::array& ray_begin, const af::array& ray_end) const override {
        uint32_t count = ray_begin.dims()[1];

        // Compute intersection of ray with a plane
        af::array has_hit = af::constant(0, count).as(b8);
        af::array hit_pos = ray_end;
        af::array a       = dot3(normal, center - ray_begin);
        af::array b       = dot3(normal, ray_end - ray_begin);
        af::array t       = af::select(b != 0.0, a / b, (double)0.0);

        af::array plane_intersect = (ray_end - ray_begin) * t + ray_begin;
        af::array dist            = norm3(plane_intersect - center);

        t = af::abs(t);

        // Determine if the intersection falls inside the disk radius and occurs
        // with the current ray segment
        has_hit = af::moddims((dist < outter_radius) && (t <= 1.0) &&
                                  (t > 0.0) && (dist > inner_radius),
                              af::dim4(count));
        hit_pos = plane_intersect;

        return {has_hit, hit_pos};
    }

    af::array get_color(const af::array& ray_begin,
                        const af::array& ray_end) const override {
        auto pair = intersect(ray_begin, ray_end);
        af::array hit = pair.first;
        af::array pos = pair.second;

        auto val = 1.f - (norm3(pos - center).T() - inner_radius) /
                             (outter_radius - inner_radius);

        af::array color =
            disk_color.T() * 1.5f * (val * val * (val * -2.f + 3.f)).as(f32);

        return af::select(af::tile(hit, af::dim4(1, 3)), color, 0.f);
    }
};