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