From 4f32039f24c0bbdc304de1d537b609c3ed750113 Mon Sep 17 00:00:00 2001
From: Robert Osfield <robert@openscenegraph.com>
Date: Tue, 19 Dec 2006 17:30:22 +0000
Subject: [PATCH] =?UTF-8?q?From=20Mathias=20Fr=C3=B6hlich,=20"I=20have=20a?=
 =?UTF-8?q?=20small=20update=20to=20the=20'non=20convex=20polygon=20detect?=
 =?UTF-8?q?ion'=20in=20the=20ac3d=20loader=20that=20is=20used=20to=20tell?=
 =?UTF-8?q?=20if=20tesselation=20is=20required=20or=20if=20we=20will=20bet?=
 =?UTF-8?q?ter=20leave=20a=20polygon=20as=20is.=20It=20is=20still=20not=20?=
 =?UTF-8?q?perfect=20but=20catches=20some=20more=20cases."?=
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---
 src/osgPlugins/ac3d/ac3d.cpp | 23 +++++++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)

diff --git a/src/osgPlugins/ac3d/ac3d.cpp b/src/osgPlugins/ac3d/ac3d.cpp
index bec58b1c1..a0f4f0f63 100644
--- a/src/osgPlugins/ac3d/ac3d.cpp
+++ b/src/osgPlugins/ac3d/ac3d.cpp
@@ -769,15 +769,34 @@ class SurfaceBin : public PrimitiveBin {
         // Compute the normal times the enclosed area.
         // During that check if the surface is convex. If so, put in the surface as such.
         bool needTesselation = false;
+        osg::Vec3 prevEdgeNormal;
         osg::Vec3 weightedNormal(0, 0, 0);
         osg::Vec3 v0 = _vertexSet->getVertex(_refs[0].index);
         for (unsigned i = 2; i < nRefs; ++i) {
             osg::Vec3 side1 = _vertexSet->getVertex(_refs[i-1].index) - v0;
             osg::Vec3 side2 = _vertexSet->getVertex(_refs[i].index) - v0;
             osg::Vec3 newNormal = side1^side2;
-            if (3 < nRefs && newNormal*weightedNormal < 0)
+            if (!needTesselation)
             {
-                needTesselation = true;
+                if (3 < nRefs && newNormal*weightedNormal < 0)
+                {
+                    needTesselation = true;
+                }
+                if (i < 3)
+                {
+                    prevEdgeNormal = newNormal;
+                }
+                else // if (3 <= i) // due to the for loop
+                {
+                    osg::Vec3 sideim1 = _vertexSet->getVertex(_refs[i-1].index) - _vertexSet->getVertex(_refs[i-2].index);
+                    osg::Vec3 sidei = _vertexSet->getVertex(_refs[i].index) - _vertexSet->getVertex(_refs[i-2].index);
+                    osg::Vec3 edgeNormal = sideim1^sidei;
+                    if (edgeNormal*prevEdgeNormal < 0)
+                    {
+                        needTesselation = true;
+                    }
+                    prevEdgeNormal = edgeNormal;
+                }
             }
 
             weightedNormal += newNormal;