Hi Stuart,
Attached is a small fix for the sorting in CloudShaderGeometry.cxx.
I think the sorting problem stems from the osg idiosyncracy
to store transposed matrices...so the intuitive
osg::Vec4f p = vm * osg::Vec4f(_cloudsprites[i]->position.osg(), 1.0f);
needs to be replaced with...
osg::Vec4f p = vm.preMult(osg::Vec4f(_cloudsprites[i]->position.osg(),
1.0f);
The patch also optimizes the distance calculation - it evaluates the distances
in model space instead of eye space, which reduces computation to a dot-
product instead of a matrix multiplication.
bye,
Manuel
Index: CloudShaderGeometry.cxx
===================================================================
RCS file: /var/cvs/SimGear-0.3/source/simgear/scene/sky/CloudShaderGeometry.cxx,v
retrieving revision 1.2
diff -u -r1.2 CloudShaderGeometry.cxx
--- CloudShaderGeometry.cxx 6 Nov 2008 21:58:07 -0000 1.2
+++ CloudShaderGeometry.cxx 9 Nov 2008 03:34:23 -0000
@@ -34,27 +34,32 @@
{
void CloudShaderGeometry::drawImplementation(RenderInfo& renderInfo) const
{
+ if (!_cloudsprites.size()) return;
+
osg::State& state = *renderInfo.getState();
osg::Matrix vm = state.getModelViewMatrix();
//TODO: It isn't clear whether this is worth the perf hit ATM.
- // 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--)
+ // 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++)
{
- 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())
- {
+ 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;
}
+ else
+ p = q;
}
-
+
const Extensions* extensions = getExtensions(state.getContextID(),true);
for(CloudSpriteList::const_iterator t = _cloudsprites.begin(); t != _cloudsprites.end(); ++t)
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