- osg::Matrix vm = state.getModelViewMatrix();
-
- //TODO: It isn't clear whether this is worth the perf hit ATM.
-
- // Transform the viewing direction, represented by the eye space vector (0,0,-1, 0), into model-space
- // (here we simply take the opposite direction and reverse the ordering when sorting)
- osg::Vec3f view_dir(vm(0, 2), vm(1, 2), vm(2, 2)); // Caveat: OpenSceneGraph matrices are transposed!
-
- float p = view_dir*_cloudsprites[0]->position.osg();
- // Do a single iteration of a bubble sort, sorting
- // back to front.
- for(int i = 0; i < _cloudsprites.size() - 1; i++)
- {
- float q = view_dir*_cloudsprites[i+1]->position.osg();
- if (p > q) {
- CloudSprite c = *_cloudsprites[i];
- *_cloudsprites[i] = *_cloudsprites[i+1];
- *_cloudsprites[i+1] = c;
+ 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();