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   m_min = Vec3f(Infinity, Infinity, Infinity);
  35   m_max = Vec3f(-Infinity, -Infinity, -Infinity);
  36 }
  37
  38 void
  39 Box::Extend(const Vec3f& a)
  40 {
  41   // for all three coordinates, move m_max or m_min to the point
  42   for(size_t i = 0; i < 3; i++) {
  43     if(a[i] > m_max[i]) {
  44       m_max[i] = a[i];
  45     }
  46     if(a[i] < m_min[i]) {
  47       m_min[i] = a[i];
  48     } // else: do nothing, coordinate is inside the box
  49   }
  50 }
  51
  52 void
  53 Box::Extend(const Box& box)
  54 {
  55   Extend(box.min());
  56   Extend(box.max());
  57 }
  58
  59 bool Box::OverlapsHelper(Box b) const {
  60   bool overlaps = true;
  61   for(size_t i = 0; i < 3; i++) {
  62     overlaps &=
  63       (m_min[i] < b.min()[i] && b.min()[i] < m_max[i]) ||
  64       (m_min[i] < b.max()[i] && b.min()[i] < m_max[i]) ||
  65       (m_min[i] > b.min()[i] && b.min()[i] > m_max[i]) ||
  66       (m_min[i] > b.max()[i] && b.min()[i] > m_max[i]);
  67   }
  68   return overlaps;
  69 }
  70
  71 bool
  72 Box::Overlaps(const Box& b) const
  73 {
  74   // Boxes overlap if b.m_min or b.m_max are between our m_max and m_min
  75   // for all dimensions
  76   bool overlaps = OverlapsHelper(b);
  77
  78   // if that is not enough, swap y coordinates, we could have the following
  79   // (sample for 2-dimensional case):
  80   //      o----------
  81   //      |         |      + denotes crossing,
  82   // -----+----o    |      o denotes min/max point
  83   // |    |    |    |
  84   // |    -----+----o
  85   // |         |
  86   // o----------
  87   if(!overlaps) {
  88     Vec3f min = b.min();
  89     Vec3f max = b.max();
  90     Vec3f new_min(min[0], max[1], min[2]);
  91     Vec3f new_max(max[0], min[1], max[2]);
  92     Box new_y_box(new_min, new_max);
  93     overlaps = OverlapsHelper(new_y_box);
  94
  95     // and now for y and z coordinates also
  96     if(!overlaps) {
  97       min = new_y_box.min();
  98       max = new_y_box.max();
  99       new_min = Vec3f(min[0], min[1], max[2]);
 100       new_max = Vec3f(max[0], max[1], min[2]);
 101       Box new_yz_box(new_min, new_max);
 102       overlaps = OverlapsHelper(new_yz_box);
 103
 104       // and now for only z coordinates
 105       if(!overlaps) {
 106         min = new_y_box.min();
 107         max = new_y_box.max();
 108         new_min = Vec3f(min[0], max[1], min[2]);
 109         new_max = Vec3f(max[0], min[1], max[2]);
 110         Box new_z_box(new_min, new_max);
 111         overlaps = OverlapsHelper(new_z_box);
 112         // at this point, we do not need to swap further, as either m_max or
 113         // m_min has been tested inside b.
 114       }
 115     }
 116   }
 117
 118   return overlaps;
 119 }
 120
 121 void
 122 Box::Clip(const Ray& ray, float& tnear, float& tfar) const
 123 {
 124   // Note: equations here are the same as in InfinitePlane::Intersect()
 125   // t = ((o-a)*n) / (d*n)
 126   // o = ray.origin(), d = ray.direction(),
 127   // n = surface normal of plane, a = anchor point of plane
 128   Vec3f diff_min = m_min - ray.origin(); // o-a
 129   Vec3f diff_max = m_max - ray.origin();
 130
 131   float cos_theta, temp;
 132   float tx_near = -Infinity, tx_far = Infinity,
 133     ty_near = -Infinity, ty_far = Infinity,
 134     tz_near = -Infinity, tz_far = Infinity;
 135
 136   // clip along x axis
 137   if((cos_theta = ray.direction().dot(Vec3f(1,0,0))) != 0) // if not parallel...
 138     tx_near = diff_min.dot(Vec3f(1,0,0)) / cos_theta;
 139   if((cos_theta = ray.direction().dot(Vec3f(1,0,0))) != 0)
 140     tx_far = diff_max.dot(Vec3f(1,0,0)) / cos_theta;
 141
 142   // we don't know which is nearer, m_min or m_max, so swap them if neccessary
 143   if(tx_near > tx_far) {
 144     temp = tx_near;
 145     tx_near = tx_far;
 146     tx_far = temp;
 147   }
 148
 149   // do the same for y axis
 150   if((cos_theta = ray.direction().dot(Vec3f(0,1,0))) != 0)
 151     ty_near = diff_min.dot(Vec3f(0,1,0)) / cos_theta;
 152   if((cos_theta = ray.direction().dot(Vec3f(0,1,0))) != 0)
 153     ty_far = diff_max.dot(Vec3f(0,1,0)) / cos_theta;
 154   if(ty_near > ty_far) {
 155     temp = ty_near;
 156     ty_near = ty_far;
 157     ty_far = temp;
 158   }
 159
 160   // ...and for z axis
 161   if((cos_theta = ray.direction().dot(Vec3f(0,0,1))) != 0)
 162     tz_near = diff_min.dot(Vec3f(0,0,1)) / cos_theta;
 163   if((cos_theta = ray.direction().dot(Vec3f(0,0,1))) != 0)
 164     tz_far = diff_max.dot(Vec3f(0,0,1)) / cos_theta;
 165   if(tz_near > tz_far) {
 166     temp = tz_near;
 167     tz_near = tz_far;
 168     tz_far = temp;
 169   }
 170
 171   // now the maximum of "near"s is the entry point of the ray, the minimum
 172   // of "far"s is the ray's exit point. Visually speaking: the ray must cross
 173   // all three "near" planes before it can be inside the box.
 174   // Note: If t_near_max > t_far_min, the ray does not intersect the box
 175   tnear = fmax(fmax(tx_near, ty_near), tz_near);
 176   tfar = fmin(fmin(tx_far, ty_far), tz_far);
 177 }
 178
 179 const Vec3f&
 180 Box::min() const
 181 {
 182   return m_min;
 183 }
 184
 185 const Vec3f&
 186 Box::max() const
 187 {
 188   return m_max;
 189 }