cone.cpp

Go to the documentation of this file.

/*
    pbrt source code Copyright(c) 1998-2010 Matt Pharr and Greg Humphreys.

    This file is part of pbrt.

    pbrt is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.  Note that the text contents of
    the book "Physically Based Rendering" are *not* licensed under the
    GNU GPL.

    pbrt is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.

 */


// shapes/cone.cpp*
#include "stdafx.h"
#include "shapes/cone.h"
#include "paramset.h"

// Cone Method Definitions
Cone::Cone(const Transform *o2w, const Transform *w2o, bool ro,
           float ht, float rad, float tm)
    : Shape(o2w, w2o, ro) {
    radius = rad;
    height = ht;
    phiMax = Radians( Clamp( tm, 0.0f, 360.0f ) );
}


BBox Cone::ObjectBound() const {
    Point p1 = Point( -radius, -radius, 0 );
    Point p2 = Point(  radius,  radius, height );
    return BBox( p1, p2 );
}


bool Cone::Intersect(const Ray &r, float *tHit, float *rayEpsilon,
        DifferentialGeometry *dg) const {
    float phi;
    Point phit;
    // Transform _Ray_ to object space
    Ray ray;
    (*WorldToObject)(r, &ray);

    // Compute quadratic cone coefficients
    float k = radius / height;
    k = k*k;
    float A = ray.d.x * ray.d.x + ray.d.y * ray.d.y -
        k * ray.d.z * ray.d.z;
    float B = 2 * (ray.d.x * ray.o.x + ray.d.y * ray.o.y -
        k * ray.d.z * (ray.o.z-height) );
    float C = ray.o.x * ray.o.x + ray.o.y * ray.o.y -
        k * (ray.o.z -height) * (ray.o.z-height);

    // Solve quadratic equation for _t_ values
    float t0, t1;
    if (!Quadratic(A, B, C, &t0, &t1))
        return false;

    // Compute intersection distance along ray
    if (t0 > ray.maxt || t1 < ray.mint)
        return false;
    float thit = t0;
    if (t0 < ray.mint) {
        thit = t1;
        if (thit > ray.maxt) return false;
    }

    // Compute cone inverse mapping
    phit = ray(thit);
    phi = atan2f(phit.y, phit.x);
    if (phi < 0.) phi += 2.f*M_PI;

    // Test cone intersection against clipping parameters
    if (phit.z < 0 || phit.z > height || phi > phiMax) {
        if (thit == t1) return false;
        thit = t1;
        if (t1 > ray.maxt) return false;
        // Compute cone inverse mapping
        phit = ray(thit);
        phi = atan2f(phit.y, phit.x);
        if (phi < 0.) phi += 2.f*M_PI;
        if (phit.z < 0 || phit.z > height || phi > phiMax)
            return false;
    }

    // Find parametric representation of cone hit
    float u = phi / phiMax;
    float v = phit.z / height;

    // Compute cone $\dpdu$ and $\dpdv$
    Vector dpdu(-phiMax * phit.y, phiMax * phit.x, 0);
    Vector dpdv(-phit.x / (1.f - v),
                -phit.y / (1.f - v), height);

    // Compute cone $\dndu$ and $\dndv$
    Vector d2Pduu = -phiMax * phiMax *
                    Vector(phit.x, phit.y, 0.);
    Vector d2Pduv = phiMax / (1.f - v) *
                    Vector(-phit.y, -phit.x, 0.);
    Vector d2Pdvv(0, 0, 0);

    // Compute coefficients for fundamental forms
    float E = Dot(dpdu, dpdu);
    float F = Dot(dpdu, dpdv);
    float G = Dot(dpdv, dpdv);
    Vector N = Normalize(Cross(dpdu, dpdv));
    float e = Dot(N, d2Pduu);
    float f = Dot(N, d2Pduv);
    float g = Dot(N, d2Pdvv);

    // Compute $\dndu$ and $\dndv$ from fundamental form coefficients
    float invEGF2 = 1.f / (E*G - F*F);
    Normal dndu = Normal((f*F - e*G) * invEGF2 * dpdu +
                         (e*F - f*E) * invEGF2 * dpdv);
    Normal dndv = Normal((g*F - f*G) * invEGF2 * dpdu +
                         (f*F - g*E) * invEGF2 * dpdv);

    // Initialize _DifferentialGeometry_ from parametric information
    const Transform &o2w = *ObjectToWorld;
    *dg = DifferentialGeometry(o2w(phit), o2w(dpdu), o2w(dpdv),
                               o2w(dndu), o2w(dndv), u, v, this);

    // Update _tHit_ for quadric intersection
    *tHit = thit;

    // Compute _rayEpsilon_ for quadric intersection
    *rayEpsilon = 5e-4f * *tHit;
    return true;
}



bool Cone::IntersectP(const Ray &r) const {
    float phi;
    Point phit;
    // Transform _Ray_ to object space
    Ray ray;
    (*WorldToObject)(r, &ray);

    // Compute quadratic cone coefficients
    float k = radius / height;
    k = k*k;
    float A = ray.d.x * ray.d.x + ray.d.y * ray.d.y -
        k * ray.d.z * ray.d.z;
    float B = 2 * (ray.d.x * ray.o.x + ray.d.y * ray.o.y -
        k * ray.d.z * (ray.o.z-height) );
    float C = ray.o.x * ray.o.x + ray.o.y * ray.o.y -
        k * (ray.o.z -height) * (ray.o.z-height);

    // Solve quadratic equation for _t_ values
    float t0, t1;
    if (!Quadratic(A, B, C, &t0, &t1))
        return false;

    // Compute intersection distance along ray
    if (t0 > ray.maxt || t1 < ray.mint)
        return false;
    float thit = t0;
    if (t0 < ray.mint) {
        thit = t1;
        if (thit > ray.maxt) return false;
    }

    // Compute cone inverse mapping
    phit = ray(thit);
    phi = atan2f(phit.y, phit.x);
    if (phi < 0.) phi += 2.f*M_PI;

    // Test cone intersection against clipping parameters
    if (phit.z < 0 || phit.z > height || phi > phiMax) {
        if (thit == t1) return false;
        thit = t1;
        if (t1 > ray.maxt) return false;
        // Compute cone inverse mapping
        phit = ray(thit);
        phi = atan2f(phit.y, phit.x);
        if (phi < 0.) phi += 2.f*M_PI;
        if (phit.z < 0 || phit.z > height || phi > phiMax)
            return false;
    }
    return true;
}


float Cone::Area() const {
    return phiMax*height*height*
        sqrtf((height*height)+
              (radius*radius))/(2.0f*radius);
}


Cone *CreateConeShape(const Transform *o2w, const Transform *w2o,
        bool reverseOrientation, const ParamSet &params) {
    float radius = params.FindOneFloat("radius", 1);
    float height = params.FindOneFloat("height", 1);
    float phimax = params.FindOneFloat("phimax", 360);
    return new Cone(o2w, w2o, reverseOrientation, height, radius, phimax);
}

---