anchor.diff:              modelsRow3Ptr.Free ()
   
           // draw geometry
  -        OpenGL.Gl.DrawElementsInstanced (OpenGL.PrimitiveType.Triangles, 36, OpenGL.DrawElementsType.UnsignedInt, nativeint 0, modelsCount) // TODO: 3D: pass in mode and count.
  +        OpenGL.Gl.DrawElementsInstanced (geometry.PrimitiveType, geometry.ElementCount, OpenGL.DrawElementsType.UnsignedInt, nativeint 0, modelsCount)
           Assert ()
   
           // teardown geometry
  
positive.code:     type [<StructuralEquality; NoComparison>] PhysicallyBasedGeometry =
          { VertexBuffer : uint
            IndexBuffer : uint
            PhysicallyBasedVao : uint }
  
      /// Assert a lack of Gl error. Has an generic parameter to enable value pass-through.
  
negative.code:         // make physically based geometry
          { VertexBuffer = vertexBuffer
            IndexBuffer = indexBuffer
            PrimitiveType = OpenGL.PrimitiveType.Triangles
            ElementCount = 36
            PhysicallyBasedVao = vao }
  
      /// Draw a sprite whose indices and vertices were created by OpenGL.Gl.CreateSpriteQuad and whose uniforms and shader match those of OpenGL.CreateSpriteShader.
  