From fd327f68f603ee613a3f460d93f8d8ebaed88c82 Mon Sep 17 00:00:00 2001
From: Robert Osfield <robert@openscenegraph.com>
Date: Thu, 28 Oct 2004 13:26:06 +0000
Subject: [PATCH] From Tom Jolley, Added a new enum POINT_ROT_WORLD_Z_AXIS and
 a new section in computeMatrix for this enum. With a small tweak from Robert
 Osfield to set _cacheMode.

---
 include/osg/Billboard |  1 +
 src/osg/Billboard.cpp | 29 +++++++++++++++++++++++++++++
 2 files changed, 30 insertions(+)

diff --git a/include/osg/Billboard b/include/osg/Billboard
index 2d1608465..12fdeedc6 100644
--- a/include/osg/Billboard
+++ b/include/osg/Billboard
@@ -112,6 +112,7 @@ class SG_EXPORT Billboard : public Geode
             AXIAL_ROT_X_AXIS=AXIAL_ROT+1,
             AXIAL_ROT_Y_AXIS,
             AXIAL_ROT_Z_AXIS,
+            POINT_ROT_WORLD_Z_AXIS,
             CACHE_DIRTY
         };
 
diff --git a/src/osg/Billboard.cpp b/src/osg/Billboard.cpp
index 4725698c8..381e77f30 100644
--- a/src/osg/Billboard.cpp
+++ b/src/osg/Billboard.cpp
@@ -70,6 +70,12 @@ void Billboard::updateCache()
         else if (_axis==Vec3(0.0f,0.0,1.0f) && _normal==Vec3(0.0f,-1.0,0.0f)) _cachedMode = AXIAL_ROT_Z_AXIS;
         else                                                                  _cachedMode = AXIAL_ROT;
     }
+    else if( _mode == POINT_ROT_WORLD )
+    {
+        if(_axis==Vec3(0.0f, 0.0, 1.0f) && _normal==Vec3(0.0f, -1.0f, 0.0f))  _cachedMode = POINT_ROT_WORLD_Z_AXIS;
+        else _cachedMode = _mode;
+       
+    }
     else _cachedMode = _mode;
     
     _side = _axis^_normal;
@@ -226,6 +232,29 @@ bool Billboard::computeMatrix(Matrix& modelview, const Vec3& eye_local, const Ve
             }
             break;
         }
+        case(POINT_ROT_WORLD_Z_AXIS):
+        {
+           // float rotation_about_z = atan2( -ev.y(), ev.x() );
+           // float xy_distance = sqrt( ev.x()*ev.x() + ev.y()*ev.y() );
+           // float rotation_from_xy = atan2( xy_distance, -ev.z() );
+
+           Vec2   about_z( -ev.y(), ev.x() );
+           if( about_z.normalize() == 0.0f ) about_z.x() = 1.0f;
+           float  xy_distance = sqrt( ev.x()*ev.x() + ev.y()*ev.y() );
+           Vec2   from_xy( xy_distance, -ev.z() );
+           if( from_xy.normalize() == 0.0f ) from_xy.x() = 1.0f;
+
+           matrix(0,0) =  about_z.x();
+           matrix(0,1) =  about_z.y();
+           matrix(1,0) = -about_z.y()*from_xy.x();
+           matrix(1,1) =  about_z.x()*from_xy.x();
+           matrix(1,2) =  from_xy.y();
+           matrix(2,0) =  about_z.y()*from_xy.y();
+           matrix(2,1) = -about_z.x()*from_xy.y();
+           matrix(2,2) =  from_xy.x();
+
+           break;
+        }
     }
 
     matrix.setTrans(pos_local);