/home/cube/sources/osgearth/src/osgEarthDrivers/engine_osgterrain/LODFactorCallback.cpp

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/* -*-c++-*- */
/* osgEarth - Dynamic map generation toolkit for OpenSceneGraph
 * Copyright 2008-2011 Pelican Mapping
 * http://osgearth.org
 *
 * osgEarth is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program 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 Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>
 */
#include "LODFactorCallback"

#include <osg/Math>
#include <osg/PagedLOD>
#include <osg/StateSet>
#include <osg/Uniform>
#include <osgUtil/CullVisitor>

namespace osgEarth
{
    namespace Drivers
    {
        // This callback sets a uniform, osgearth_LODRangeFactor, based on the
        // distance from the camera and its relation to the minimum and
        // maximum distance for a tile. The maximum distance isn't actually
        // available, so 2 * min distance is used as an estimate. The range
        // factor's value goes from 0 - at the maximum range - to 1 for the
        // minimum range.

        void LODFactorCallback::operator()(osg::Node* node, osg::NodeVisitor* nv)
        {
            // test the type since this is not always a PagedLOD.
            osg::PagedLOD* lod = static_cast<osg::PagedLOD*>(node);
            osgUtil::CullVisitor* cv = static_cast<osgUtil::CullVisitor*>(nv);
            osg::LOD::RangeMode rangeMode = lod->getRangeMode();
            float requiredRange = 0.0f;
            float rangeFactor = 1.0f;
            const osg::LOD::RangeList& rangeList = lod->getRangeList();
            if (rangeMode == osg::LOD::DISTANCE_FROM_EYE_POINT)
            {
                requiredRange = cv->getDistanceToViewPoint(lod->getCenter(), true);
            }
            else if (cv->getLODScale() > 0.0f)
            {
                requiredRange = cv->clampedPixelSize(lod->getBound()) / cv->getLODScale();
            }
            else
            {
                // The comment in osg/PagedLOD.cpp says that this algorithm
                // finds the highest res tile, but it actually finds the
                // lowest res tile!
                for (osg::LOD::RangeList::const_iterator itr = rangeList.begin(), end = rangeList.end();
                    itr != end;
                    ++itr)
                {
                    requiredRange = osg::maximum(requiredRange, itr->first);
                }
            }
            // We're counting on only finding one valid LOD, unlike the
            // general OSG behavior.
            if (!rangeList.empty() && rangeList[0].first <= requiredRange
                && requiredRange < rangeList[0].second)
            {
                rangeFactor = 1.0f - (requiredRange - rangeList[0].first) / rangeList[0].first;
                rangeFactor = osg::clampTo(rangeFactor, 0.0f, 1.0f);
            }
            osg::ref_ptr<osg::Uniform> ufact
                = new osg::Uniform("osgearth_LODRangeFactor", rangeFactor);
            osg::ref_ptr<osg::StateSet> ss = new osg::StateSet;
            ss->addUniform(ufact.get());

            cv->pushStateSet(ss.get());
            traverse(node, nv);
            cv->popStateSet();
        }
    }
}