aabb.h

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Copyright (c) 2020 Advanced Micro Devices, Inc. All rights reserved.
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#pragma once
#include <cfloat>
#include <ostream>

#include "float2.h"
#include "float3.h"

namespace bvh
{
struct Aabb
{
    //<! Create AABB from a single point.
    Aabb() : pmin{FLT_MAX, FLT_MAX, FLT_MAX}, pmax{-FLT_MAX, -FLT_MAX, -FLT_MAX} {}
    //<! Create AABB from a single point.
    Aabb(const float3& p) : pmin(p), pmax(p) {}
    //<! Create AABB from min and max points.
    Aabb(const float3& mi, const float3& ma) : pmin(mi), pmax(ma) {}
    //<! Create AABB from another AABB.
    Aabb(const Aabb& rhs) : pmin(rhs.pmin), pmax(rhs.pmax) {}
    //<! Grow AABB to enclose itself and another AABB.
    Aabb& Grow(const Aabb& rhs)
    {
        pmin = vmin(pmin, rhs.pmin);
        pmax = vmax(pmax, rhs.pmax);
        return *this;
    }
    //<! Grow AABB to enclose itself and another point.
    Aabb& Grow(const float3& p)
    {
        pmin = vmin(pmin, p);
        pmax = vmax(pmax, p);
        return *this;
    }
    //<! Box center.
    float3 Center() const { return (pmax + pmin) * 0.5; }

    //<! Box extens along each axe.
    float3 Extents() const { return pmax - pmin; }
    //<! Calculate AABB union.
    static Aabb Union(const Aabb& rhs, const Aabb& lhs)
    {
        Aabb result(vmin(lhs.pmin, rhs.pmin), vmax(lhs.pmax, rhs.pmax));
        return result;
    }

    //<! Box extens along each axe.
    float Area() const
    {
        float3 ext = Extents();
        return 2 * (ext.x * ext.y + ext.x * ext.z + ext.y * ext.z);
    }

    //<! Calculate AABB vs ray intersection distances.
    float2 Intersect(const float3& invD, const float3& oxInvD, float minT, float maxT) const
    {
        float3 f    = fma(pmax, invD, oxInvD);
        float3 n    = fma(pmin, invD, oxInvD);
        float3 tmax = vmax(f, n);
        float3 tmin = vmin(f, n);
        float  t1   = fminf(fminf(fminf(tmax.x, tmax.y), tmax.z), maxT);
        float  t0   = fmaxf(fmaxf(fmaxf(tmin.x, tmin.y), tmin.z), minT);
        return float2{t0, t1};
    }

    bool Includes(Aabb const& rhs) const
    {
        float3 min_diff = rhs.pmin - pmin;
        float3 max_diff = pmax - rhs.pmax;
        return !(min_diff.x < -1e-8f || min_diff.y < -1e-8f || min_diff.z < -1e-8f || max_diff.x < -1e-8f ||
                 max_diff.y < -1e-8f || max_diff.z < -1e-8f);
    }

    //<! Min point of AABB.
    float3 pmin;
    //<! Max point of AABB.
    float3 pmax;
};

inline std::ostream& operator<<(std::ostream& oss, const Aabb& aabb)
{
    oss << "{ min: [" << aabb.pmin.x << ", " << aabb.pmin.y << ", " << aabb.pmin.z << "], ";
    oss << " max: [" << aabb.pmax.x << ", " << aabb.pmax.y << ", " << aabb.pmax.z << "] }";
    return oss;
}
}  // namespace bvh