From Jason Daly, "Currently, the .mdl plugin loads vertices in the native DirectX order, which is the reverse of OpenGL order. This means that the back faces are currently rendered as front faces, and vice versa.

This fix reverses the vertex order and sets up proper OpenGL facing.  I didn't notice this problem until I started using the plug-in in my own code (osgviewer seems to not enable backface culling)."

src/osgPlugins/mdl/VTXReader.cpp

@@ -328,6 +328,7 @@ ref_ptr<PrimitiveSet> VTXReader::processStrip(unsigned short * indexArray,
                                               int offset)
 {
     VTXStrip                strip;
+    DrawElementsUShort *    drawElements;
     ref_ptr<PrimitiveSet>   primSet;
     unsigned short *        start;
     unsigned short *        end;
@@ -348,13 +349,17 @@ ref_ptr<PrimitiveSet> VTXReader::processStrip(unsigned short * indexArray,
 
     // Create the primitive set (based on the flag)
     if (strip.strip_flags & STRIP_IS_TRI_LIST)
-        primSet =
+        drawElements =
             new DrawElementsUShort(PrimitiveSet::TRIANGLES, start, end);
     else
-        primSet =
+        drawElements =
             new DrawElementsUShort(PrimitiveSet::TRIANGLE_STRIP, start, end);
 
+    // Flip the indices to get the front faces correct
+    std::reverse(drawElements->begin(), drawElements->end());
+
     // Return the primitive set
+    primSet = drawElements;
     return primSet;
 }