OpenSceneGraph/examples/osgdepthpartition/DistanceAccumulator.cpp

#include "DistanceAccumulator.h"
#include <osg/Geode>
#include <osg/Transform>
#include <osg/Projection>
#include <algorithm>
#include <math.h>

/** Function that sees whether one DistancePair should come before another in
    an sorted list. Used to sort the vector of DistancePairs. */
bool precedes(const DistanceAccumulator::DistancePair &a, 
              const DistanceAccumulator::DistancePair &b)
{
    // This results in sorting in order of descending far distances
    if(a.second > b.second) return true;
    else return false;
}

/** Computes distance betwen a point and the viewpoint of a matrix */
double distance(const osg::Vec3 &coord, const osg::Matrix& matrix)
{
    return -( coord[0]*matrix(0,2) + coord[1]*matrix(1,2) +
              coord[2]*matrix(2,2) + matrix(3,2) );
}

#define CURRENT_CLASS DistanceAccumulator
CURRENT_CLASS::CURRENT_CLASS()
    : osg::NodeVisitor(TRAVERSE_ALL_CHILDREN), 
      _nearFarRatio(0.0005), _maxDepth(UINT_MAX)
{
    setMatrices(osg::Matrix::identity(), osg::Matrix::identity());
    reset();
}

CURRENT_CLASS::~CURRENT_CLASS() {}

void CURRENT_CLASS::pushLocalFrustum()
{
    osg::Matrix& currMatrix = _viewMatrices.back();

        // Compute the frustum in local space
        osg::Polytope localFrustum;
        localFrustum.setToUnitFrustum(false, false);
        localFrustum.transformProvidingInverse(currMatrix*_projectionMatrices.back());
        _localFrusta.push_back(localFrustum);

        // Compute new bounding box corners
        bbCornerPair corner;
        corner.second = (currMatrix(0,2)<=0?1:0) |
                        (currMatrix(1,2)<=0?2:0) |
                        (currMatrix(2,2)<=0?4:0);
        corner.first = (~corner.second)&7;
        _bbCorners.push_back(corner);
}

void CURRENT_CLASS::pushDistancePair(double zNear, double zFar)
{
    if(zFar > 0.0) // Make sure some of drawable is visible
    {
      // Make sure near plane is in front of viewpoint.
      if(zNear <= 0.0)
      {
        zNear = zFar*_nearFarRatio;
        if(zNear >= 1.0) zNear = 1.0; // 1.0 limit chosen arbitrarily!
      }

      // Add distance pair for current drawable
      _distancePairs.push_back(DistancePair(zNear, zFar));

      // Override the current nearest/farthest planes if necessary
      if(zNear < _limits.first) _limits.first = zNear;
      if(zFar > _limits.second) _limits.second = zFar;
    }
}

/** Return true if the node should be traversed, and false if the bounding sphere
    of the node is small enough to be rendered by one CameraNode. If the latter
    is true, then store the node's near & far plane distances. */
bool CURRENT_CLASS::shouldContinueTraversal(osg::Node &node)
{
    // Allow traversal to continue if we haven't reached maximum depth.
    bool keepTraversing = (_currentDepth < _maxDepth);

    const osg::BoundingSphere &bs = node.getBound();
    double zNear = 0.0, zFar = 0.0;

    // Make sure bounding sphere is valid and within viewing volume
    if(bs.valid())
    {
      if(!_localFrusta.back().contains(bs)) keepTraversing = false;
      else
      {
        // Compute near and far planes for this node
        zNear = distance(bs._center, _viewMatrices.back());
        zFar = zNear + bs._radius;
        zNear -= bs._radius;

        // If near/far ratio is big enough, then we don't need to keep
        // traversing children of this node.
        if(zNear >= zFar*_nearFarRatio) keepTraversing = false;
      }
    }

    // If traversal should stop, then store this node's (near,far) pair
    if(!keepTraversing) pushDistancePair(zNear, zFar);

    return keepTraversing;
}

void CURRENT_CLASS::apply(osg::Node &node)
{
    if(shouldContinueTraversal(node))
    {
      // Traverse this node
      _currentDepth++;
      traverse(node);
      _currentDepth--;
    }
}

void CURRENT_CLASS::apply(osg::Projection &proj)
{
    if(shouldContinueTraversal(proj))
    {
      // Push the new projection matrix view frustum
      _projectionMatrices.push_back(proj.getMatrix());
      pushLocalFrustum();

      // Traverse the group
      _currentDepth++;
      traverse(proj);
      _currentDepth--;

      // Reload original matrix and frustum
      _localFrusta.pop_back();
      _bbCorners.pop_back();
      _projectionMatrices.pop_back();
    }
}

void CURRENT_CLASS::apply(osg::Transform &transform)
{
    if(shouldContinueTraversal(transform))
    {
      // Compute transform for current node
      osg::Matrix currMatrix = _viewMatrices.back();
      bool pushMatrix = transform.computeLocalToWorldMatrix(currMatrix, this);

      if(pushMatrix) 
      {
        // Store the new modelview matrix and view frustum
        _viewMatrices.push_back(currMatrix);
        pushLocalFrustum();
      }

      _currentDepth++;
      traverse(transform);
      _currentDepth--;

      if(pushMatrix) 
      {
        // Restore the old modelview matrix and view frustum
        _localFrusta.pop_back();
        _bbCorners.pop_back();
        _viewMatrices.pop_back();
      }
    }
}

void CURRENT_CLASS::apply(osg::Geode &geode)
{
    // Contained drawables will only be individually considered if we are
    // allowed to continue traversing.
    if(shouldContinueTraversal(geode))
    {
      osg::Drawable *drawable;
      double zNear, zFar;

      // Handle each drawable in this geode
      for(unsigned int i = 0; i < geode.getNumDrawables(); i++)
      {
        drawable = geode.getDrawable(i);

        const osg::BoundingBox &bb = drawable->getBound();
        if(bb.valid())
        {
          // Make sure drawable will be visible in the scene
          if(!_localFrusta.back().contains(bb)) continue;

          // Compute near/far distances for current drawable
          zNear = distance(bb.corner(_bbCorners.back().first), 
                               _viewMatrices.back());
          zFar = distance(bb.corner(_bbCorners.back().second), 
                          _viewMatrices.back());
          if(zNear > zFar) std::swap(zNear, zFar);
          pushDistancePair(zNear, zFar);
        }
      }
    }
}

void CURRENT_CLASS::setMatrices(const osg::Matrix &modelview,
                                const osg::Matrix &projection)
{
    _modelview = modelview;
    _projection = projection;
}

void CURRENT_CLASS::reset()
{
    // Clear vectors & values
    _distancePairs.clear();
    _cameraPairs.clear();
    _limits.first = DBL_MAX;
    _limits.second = 0.0;
    _currentDepth = 0;

    // Initial transform matrix is the modelview matrix
    _viewMatrices.clear();
    _viewMatrices.push_back(_modelview);

    // Set the initial projection matrix
    _projectionMatrices.clear();
    _projectionMatrices.push_back(_projection);

    // Create a frustum without near/far planes, for cull computations
    _localFrusta.clear();
    _bbCorners.clear();
    pushLocalFrustum();
}

void CURRENT_CLASS::computeCameraPairs()
{
    // Nothing in the scene, so no cameras needed
    if(_distancePairs.empty()) return;

    // Entire scene can be handled by just one camera
    if(_limits.first >= _limits.second*_nearFarRatio)
    {
      _cameraPairs.push_back(_limits);
      return;
    }

    PairList::iterator i,j;

    // Sort the list of distance pairs by descending far distance
    std::sort(_distancePairs.begin(), _distancePairs.end(), precedes);

    // Combine overlapping distance pairs. The resulting set of distance
    // pairs (called combined pairs) will not overlap.
    PairList combinedPairs;
    DistancePair currPair = _distancePairs.front();
    for(i = _distancePairs.begin(); i != _distancePairs.end(); i++)
    {
      // Current distance pair does not overlap current combined pair, so
      // save the current combined pair and start a new one.
      if(i->second < 0.99*currPair.first)
      {
        combinedPairs.push_back(currPair);
        currPair = *i;
      }

      // Current distance pair overlaps current combined pair, so expand
      // current combined pair to encompass distance pair.
      else
        currPair.first = std::min(i->first, currPair.first);
    }
    combinedPairs.push_back(currPair); // Add last pair

    // Compute the (near,far) distance pairs for each camera.
    // Each of these distance pairs is called a "view segment".
    double currNearLimit, numSegs, new_ratio;
    double ratio_invlog = 1.0/log(_nearFarRatio);
    unsigned int temp;
    for(i = combinedPairs.begin(); i != combinedPairs.end(); i++)
    {
      currPair = *i; // Save current view segment

      // Compute the fractional number of view segments needed to span
      // the current combined distance pair.
      currNearLimit = currPair.second*_nearFarRatio;
      if(currPair.first >= currNearLimit) numSegs = 1.0;
      else 
      {
        numSegs = log(currPair.first/currPair.second)*ratio_invlog;

        // Compute the near plane of the last view segment
        //currNearLimit *= pow(_nearFarRatio, -floor(-numSegs) - 1);
        for(temp = (unsigned int)(-floor(-numSegs)); temp > 1; temp--)
        {
          currNearLimit *= _nearFarRatio;
        }
      }

      // See if the closest view segment can absorb other combined pairs
      for(j = i+1; j != combinedPairs.end(); j++)
      {
        // No other distance pairs can be included
        if(j->first < currNearLimit) break;
      }

      // If we did absorb another combined distance pair, recompute the
      // number of required view segments.
      if(i != j-1)
      {
        i = j-1;
        currPair.first = i->first;
        if(currPair.first >= currPair.second*_nearFarRatio) numSegs = 1.0;
        else numSegs = log(currPair.first/currPair.second)*ratio_invlog;
      }

      /* Compute an integer number of segments by rounding the fractional
         number of segments according to how many segments there are.
         In general, the more segments there are, the more likely that the 
         integer number of segments will be rounded down.
         The purpose of this is to try to minimize the number of view segments
         that are used to render any section of the scene without violating
         the specified _nearFarRatio by too much. */
      if(numSegs < 10.0) numSegs = floor(numSegs + 1.0 - 0.1*floor(numSegs));
      else numSegs = floor(numSegs);


      // Compute the near/far ratio that will be used for each view segment
      // in this section of the scene.
      new_ratio = pow(currPair.first/currPair.second, 1.0/numSegs);

      // Add numSegs new view segments to the camera pairs list
      for(temp = (unsigned int)numSegs; temp > 0; temp--)
      {
        currPair.first = currPair.second*new_ratio;
        _cameraPairs.push_back(currPair);
        currPair.second = currPair.first;
      }
    }
}

void CURRENT_CLASS::setNearFarRatio(double ratio)
{
    if(ratio <= 0.0 || ratio >= 1.0) return;
    _nearFarRatio = ratio;
}
#undef CURRENT_CLASS