From e6052ef4b4895a9fee350877a912503e8ae7a616 Mon Sep 17 00:00:00 2001
From: Robert Osfield <robert@openscenegraph.com>
Date: Fri, 11 Nov 2016 17:16:40 +0000
Subject: [PATCH] Added Dragger::applyAppropriateFrontFace(StateSet*) to make
 it easy to handle inverted matrices by toggling the FrontFace to sure the
 correct face is visible.

---
 examples/osgvolume/osgvolume.cpp |  2 +-
 include/osgManipulator/Dragger   |  8 +++++++-
 src/osgManipulator/Dragger.cpp   | 22 ++++++++++++++++++++++
 src/osgVolume/Locator.cpp        |  2 +-
 4 files changed, 31 insertions(+), 3 deletions(-)

diff --git a/examples/osgvolume/osgvolume.cpp b/examples/osgvolume/osgvolume.cpp
index 29efa4e3f..e0df891b9 100644
--- a/examples/osgvolume/osgvolume.cpp
+++ b/examples/osgvolume/osgvolume.cpp
@@ -1186,7 +1186,7 @@ int main( int argc, char **argv )
             dragger->setActivationModKeyMask(osgGA::GUIEventAdapter::MODKEY_SHIFT);
             dragger->addDraggerCallback(new DraggerVolumeTileCallback(tile.get(), tile->getLocator()));
             dragger->setMatrix(osg::Matrix::translate(0.5,0.5,0.5)*tile->getLocator()->getTransform());
-
+            dragger->applyAppropriateFrontFace(dragger->getOrCreateStateSet());
 
             group->addChild(dragger.get());
 
diff --git a/include/osgManipulator/Dragger b/include/osgManipulator/Dragger
index 14cc5dede..80aadaeee 100644
--- a/include/osgManipulator/Dragger
+++ b/include/osgManipulator/Dragger
@@ -276,7 +276,13 @@ class OSGMANIPULATOR_EXPORT Dragger : public osg::MatrixTransform
         virtual void setIntersectionMask(osg::Node::NodeMask intersectionMask) { _intersectionMask = intersectionMask; }
         osg::Node::NodeMask getIntersectionMask() const { return _intersectionMask; }
 
-    protected:
+        /** Return true if the axis of the Locator are inverted requiring the faces of any cubes used from rendering to be flipped to ensure the correct front/back face is used.*/
+        bool inverted() const;
+
+        /** apply the appropriate FrontFace setting to provided StateSet to ensure that the rendering of hull of the volume is the correct orientation.*/
+        void applyAppropriateFrontFace(osg::StateSet* ss) const;
+
+protected:
 
         Dragger();
         Dragger(const Dragger& rhs, const osg::CopyOp& copyop = osg::CopyOp::SHALLOW_COPY);
diff --git a/src/osgManipulator/Dragger.cpp b/src/osgManipulator/Dragger.cpp
index 98193cf2d..339d6d5d9 100644
--- a/src/osgManipulator/Dragger.cpp
+++ b/src/osgManipulator/Dragger.cpp
@@ -15,6 +15,7 @@
 #include <osgManipulator/Dragger>
 #include <osgManipulator/Command>
 #include <osg/Material>
+#include <osg/FrontFace>
 #include <osgGA/EventVisitor>
 #include <osgViewer/View>
 #include <osg/io_utils>
@@ -200,6 +201,27 @@ Dragger::~Dragger()
 {
 }
 
+bool Dragger::inverted() const
+{
+    osg::Vec3d xAxis(_matrix(0,0), _matrix(1,0), _matrix(2,0));
+    osg::Vec3d yAxis(_matrix(0,1), _matrix(1,1), _matrix(2,1));
+    osg::Vec3d zAxis(_matrix(0,2), _matrix(1,2), _matrix(2,2));
+    double volume = (xAxis^yAxis)*zAxis;
+    return volume<0.0;
+}
+
+void Dragger::applyAppropriateFrontFace(osg::StateSet* ss) const
+{
+    osg::StateAttribute* sa = ss->getAttribute(osg::StateAttribute::FRONTFACE);
+    osg::FrontFace* ff = dynamic_cast<osg::FrontFace*>(sa);
+    if (!ff)
+    {
+        ff = new osg::FrontFace;
+        ss->setAttribute(ff);
+    }
+    ff->setMode( inverted() ? osg::FrontFace::CLOCKWISE : osg::FrontFace::COUNTER_CLOCKWISE);
+}
+
 void Dragger::setHandleEvents(bool flag)
 {
     if (_handleEvents == flag) return;
diff --git a/src/osgVolume/Locator.cpp b/src/osgVolume/Locator.cpp
index 2de869d16..982fbad80 100644
--- a/src/osgVolume/Locator.cpp
+++ b/src/osgVolume/Locator.cpp
@@ -229,7 +229,7 @@ bool Locator::inverted() const
     osg::Vec3d xAxis(_transform(0,0), _transform(1,0), _transform(2,0));
     osg::Vec3d yAxis(_transform(0,1), _transform(1,1), _transform(2,1));
     osg::Vec3d zAxis(_transform(0,2), _transform(1,2), _transform(2,2));
-    float volume = (xAxis^yAxis)*zAxis;
+    double volume = (xAxis^yAxis)*zAxis;
     return volume<0.0;
 }