cylinder.cpp

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

// Cylinder Method Definitions
Cylinder::Cylinder(const Transform *o2w, const Transform *w2o, bool ro,
                   float rad, float z0, float z1, float pm)
    : Shape(o2w, w2o, ro) {
    radius = rad;
    zmin = min(z0, z1);
    zmax = max(z0, z1);
    phiMax = Radians(Clamp(pm, 0.0f, 360.0f));
}


BBox Cylinder::ObjectBound() const {
    Point p1 = Point(-radius, -radius, zmin);
    Point p2 = Point( radius,  radius, zmax);
    return BBox(p1, p2);
}


bool Cylinder::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 cylinder coefficients
    float A = ray.d.x*ray.d.x + ray.d.y*ray.d.y;
    float B = 2 * (ray.d.x*ray.o.x + ray.d.y*ray.o.y);
    float C = ray.o.x*ray.o.x + ray.o.y*ray.o.y - radius*radius;

    // 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 cylinder hit point and $\phi$
    phit = ray(thit);
    phi = atan2f(phit.y, phit.x);
    if (phi < 0.) phi += 2.f*M_PI;

    // Test cylinder intersection against clipping parameters
    if (phit.z < zmin || phit.z > zmax || phi > phiMax) {
        if (thit == t1) return false;
        thit = t1;
        if (t1 > ray.maxt) return false;
        // Compute cylinder hit point and $\phi$
        phit = ray(thit);
        phi = atan2f(phit.y, phit.x);
        if (phi < 0.) phi += 2.f*M_PI;
        if (phit.z < zmin || phit.z > zmax || phi > phiMax)
            return false;
    }

    // Find parametric representation of cylinder hit
    float u = phi / phiMax;
    float v = (phit.z - zmin) / (zmax - zmin);

    // Compute cylinder $\dpdu$ and $\dpdv$
    Vector dpdu(-phiMax * phit.y, phiMax * phit.x, 0);
    Vector dpdv(0, 0, zmax - zmin);

    // Compute cylinder $\dndu$ and $\dndv$
    Vector d2Pduu = -phiMax * phiMax * Vector(phit.x, phit.y, 0);
    Vector d2Pduv(0, 0, 0), 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 Cylinder::IntersectP(const Ray &r) const {
    float phi;
    Point phit;
    // Transform _Ray_ to object space
    Ray ray;
    (*WorldToObject)(r, &ray);

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

    // 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 cylinder hit point and $\phi$
    phit = ray(thit);
    phi = atan2f(phit.y, phit.x);
    if (phi < 0.) phi += 2.f*M_PI;

    // Test cylinder intersection against clipping parameters
    if (phit.z < zmin || phit.z > zmax || phi > phiMax) {
        if (thit == t1) return false;
        thit = t1;
        if (t1 > ray.maxt) return false;
        // Compute cylinder hit point and $\phi$
        phit = ray(thit);
        phi = atan2f(phit.y, phit.x);
        if (phi < 0.) phi += 2.f*M_PI;
        if (phit.z < zmin || phit.z > zmax || phi > phiMax)
            return false;
    }
    return true;
}


float Cylinder::Area() const {
    return (zmax-zmin) * phiMax * radius;
}


Cylinder *CreateCylinderShape(const Transform *o2w, const Transform *w2o,
        bool reverseOrientation, const ParamSet &params) {
    float radius = params.FindOneFloat("radius", 1);
    float zmin = params.FindOneFloat("zmin", -1);
    float zmax = params.FindOneFloat("zmax", 1);
    float phimax = params.FindOneFloat("phimax", 360);
    return new Cylinder(o2w, w2o, reverseOrientation, radius, zmin, zmax, phimax);
}


Point Cylinder::Sample(float u1, float u2, Normal *Ns) const {
    float z = Lerp(u1, zmin, zmax);
    float t = u2 * phiMax;
    Point p = Point(radius * cosf(t), radius * sinf(t), z);
    *Ns = Normalize((*ObjectToWorld)(Normal(p.x, p.y, 0.)));
    if (ReverseOrientation) *Ns *= -1.f;
    return (*ObjectToWorld)(p);
}

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