public override void DrawIndexedPrimitives(int count, int startingIndex)
{
    PreDrawCommand();
    DrawElementsType elementsType = ((OpenGLIndexBuffer)IndexBuffer).ElementsType;
    int indexSize = OpenGLFormats.GetIndexFormatSize(elementsType);
    GL.DrawElements(_primitiveType, count, elementsType, new IntPtr(startingIndex * indexSize));
}