- // Do a single iteration of a bubble sort. We do this in reverse
- // so that elements closest to the camera bubble to the front than
- // the elements further away
- for(int i = (_cloudsprites.size() -2); i >= 0; i--)
- {
- osg::Vec4f p = vm * osg::Vec4f(_cloudsprites[i]->position.osg(), 1.0f);
- osg::Vec4f q = vm * osg::Vec4f(_cloudsprites[i+1]->position.osg(), 1.0f);
-
- if (p.z() > q.z())
- {
- CloudSprite c = *_cloudsprites[i];
- *_cloudsprites[i] = *_cloudsprites[i+1];
- *_cloudsprites[i+1] = c;
+ osg::State& state = *renderInfo.getState();
+ unsigned int contextID = state.getContextID();
+ SortData& sortData = _sortData[contextID];
+ int frameNumber = state.getFrameStamp()->getFrameNumber();
+
+ if (!sortData.spriteIdx)
+ sortData.spriteIdx = new SortData::SortItemList;
+ if (sortData.spriteIdx->size() < _cloudsprites.size()) {
+ for (unsigned i = sortData.spriteIdx->size(); i < (unsigned)_cloudsprites.size(); ++i)
+ sortData.spriteIdx->push_back(SortData::SortItem(i, 0.0f));
+ sortData.frameSorted = frameNumber - (sortData.skip_limit + 1);
+ }
+ // If the cloud is already sorted, then it is likely to still be sorted.
+ // Therefore we can avoid re-sorting it for a period. If it is still
+ // sorted after that period, then we can wait for a longer period before
+ // checking again. In this way, only clouds that are changing regularly
+ // are sorted.
+ if (frameNumber - sortData.skip_limit >= sortData.frameSorted) {
+ Matrix mvp = state.getModelViewMatrix() * state.getProjectionMatrix();
+ for (SortData::SortItemList::iterator itr = sortData.spriteIdx->begin(),
+ end = sortData.spriteIdx->end();
+ itr != end;
+ ++itr) {
+ Vec4f projPos
+ = Vec4f(toOsg(_cloudsprites[itr->idx].position), 1.0f) * mvp;
+ itr->depth = projPos.z() / projPos.w();