Box.cxx

   1 #include "Box.hxx"
   2 #include "InfinitePlane.hxx"
   3
   4 Box::Box() : m_min(Infinity, Infinity, Infinity),
   5   m_max(-Infinity, -Infinity, -Infinity)
   6 {
   7 }
   8
   9 Box::Box(Vec3f min, Vec3f max) : m_min(min), m_max(max)
  10 {
  11 }
  12
  13 Box::~Box()
  14 {
  15 }
  16
  17 Box::Box(const Box& b)
  18 {
  19   m_min = b.m_min;
  20   m_max = b.m_max;
  21 }
  22
  23 Box&
  24 Box::operator=(const Box& b)
  25 {
  26   m_min = b.m_min;
  27   m_max = b.m_max;
  28   return *this;
  29 }
  30
  31 void
  32 Box::Clear()
  33 {
  34 }
  35
  36 void
  37 Box::Extend(const Vec3f& a)
  38 {
  39   // for all three coordinates, move m_max or m_min to the point
  40   for(size_t i = 0; i < 3; i++) {
  41     if(a[i] > m_max[i]) {
  42       m_max[i] = a[i];
  43     } else if(a[i] < m_min[i]) {
  44       m_min[i] = a[i];
  45     } // else: do nothing, coordinate is inside the box
  46   }
  47 }
  48
  49 void
  50 Box::Extend(const Box& box)
  51 {
  52 }
  53
  54 bool Box::OverlapsHelper(Box b) const {
  55   bool overlaps = true;
  56   for(size_t i = 0; i < 3; i++) {
  57     overlaps &=
  58       (m_min[i] < b.min()[i] && b.min()[i] < m_max[i]) ||
  59       (m_min[i] < b.max()[i] && b.min()[i] < m_max[i]) ||
  60       (m_min[i] > b.min()[i] && b.min()[i] > m_max[i]) ||
  61       (m_min[i] > b.max()[i] && b.min()[i] > m_max[i]);
  62   }
  63   return overlaps;
  64 }
  65
  66 bool
  67 Box::Overlaps(const Box& b) const
  68 {
  69   // Boxes overlap if b.m_min or b.m_max are between our m_max and m_min
  70   // for all dimensions
  71   bool overlaps = OverlapsHelper(b);
  72
  73   // if that is not enough, swap y coordinates, we could have the following
  74   // (sample for 2-dimensional case):
  75   //      o----------
  76   //      |         |      + denotes crossing,
  77   // -----+----o    |      o denotes min/max point
  78   // |    |    |    |
  79   // |    -----+----o
  80   // |         |
  81   // o----------
  82   if(!overlaps) {
  83     Vec3f min = b.min();
  84     Vec3f max = b.max();
  85     Vec3f new_min(min[0], max[1], min[2]);
  86     Vec3f new_max(max[0], min[1], max[2]);
  87     Box new_y_box(new_min, new_max);
  88     overlaps = OverlapsHelper(new_y_box);
  89
  90     // and now for y and z coordinates also
  91     if(!overlaps) {
  92       min = new_y_box.min();
  93       max = new_y_box.max();
  94       new_min = Vec3f(min[0], min[1], max[2]);
  95       new_max = Vec3f(max[0], max[1], min[2]);
  96       Box new_yz_box(new_min, new_max);
  97       overlaps = OverlapsHelper(new_yz_box);
  98
  99       // and now for only z coordinates
 100       if(!overlaps) {
 101         min = new_y_box.min();
 102         max = new_y_box.max();
 103         new_min = Vec3f(min[0], max[1], min[2]);
 104         new_max = Vec3f(max[0], min[1], max[2]);
 105         Box new_z_box(new_min, new_max);
 106         overlaps = OverlapsHelper(new_z_box);
 107         // at this point, we do not need to swap further, as either m_max or
 108         // m_min has been tested inside b.
 109       }
 110     }
 111   }
 112
 113   return overlaps;
 114 }
 115
 116 void
 117 Box::Clip(const Ray& ray, float& tnear, float& tfar) const
 118 {
 119   // Note: equations here are the same as in InfinitePlane::Intersect()
 120   // t = ((o-a)*n) / (d*n)
 121   // o = ray.origin(), d = ray.direction(),
 122   // n = surface normal of plane, a = anchor point of plane
 123   Vec3f diff_min = m_min - ray.origin(); // o-a
 124   Vec3f diff_max = m_max - ray.origin();
 125
 126   float cos_theta, temp;
 127   float tx_near = -Infinity, tx_far = Infinity,
 128     ty_near = -Infinity, ty_far = Infinity,
 129     tz_near = -Infinity, tz_far = Infinity;
 130
 131   // clip along x axis
 132   if((cos_theta = ray.direction().dot(Vec3f(1,0,0))) != 0) // if not parallel...
 133     tx_near = diff_min.dot(Vec3f(1,0,0)) / cos_theta;
 134   if((cos_theta = ray.direction().dot(Vec3f(1,0,0))) != 0)
 135     tx_far = diff_max.dot(Vec3f(1,0,0)) / cos_theta;
 136
 137   // we don't know which is nearer, m_min or m_max, so swap them if neccessary
 138   if(tx_near > tx_far) {
 139     temp = tx_near;
 140     tx_near = tx_far;
 141     tx_far = temp;
 142   }
 143
 144   // do the same for y axis
 145   if((cos_theta = ray.direction().dot(Vec3f(0,1,0))) != 0)
 146     ty_near = diff_min.dot(Vec3f(0,1,0)) / cos_theta;
 147   if((cos_theta = ray.direction().dot(Vec3f(0,1,0))) != 0)
 148     ty_far = diff_max.dot(Vec3f(0,1,0)) / cos_theta;
 149   if(ty_near > ty_far) {
 150     temp = ty_near;
 151     ty_near = ty_far;
 152     ty_far = temp;
 153   }
 154
 155   // ...and for z axis
 156   if((cos_theta = ray.direction().dot(Vec3f(0,0,1))) != 0)
 157     tz_near = diff_min.dot(Vec3f(0,0,1)) / cos_theta;
 158   if((cos_theta = ray.direction().dot(Vec3f(0,0,1))) != 0)
 159     tz_far = diff_max.dot(Vec3f(0,0,1)) / cos_theta;
 160   if(tz_near > tz_far) {
 161     temp = tz_near;
 162     tz_near = tz_far;
 163     tz_far = temp;
 164   }
 165
 166   // now the maximum of "near"s is the entry point of the ray, the minimum
 167   // of "far"s is the ray's exit point. Visually speaking: the ray must cross
 168   // all three "near" planes before it can be inside the box.
 169   // Note: If t_near_max > t_far_min, the ray does not intersect the box
 170   tnear = fmax(fmax(tx_near, ty_near), tz_near);
 171   tfar = fmin(fmin(tx_far, ty_far), tz_far);
 172 }
 173
 174 const Vec3f&
 175 Box::min() const
 176 {
 177   return m_min;
 178 }
 179
 180 const Vec3f&
 181 Box::max() const
 182 {
 183   return m_max;
 184 }