text: // Copyright (c) 2014 libmv authors.
  //
  // Permission is hereby granted, free of charge, to any person obtaining a copy
  // of this software and associated documentation files (the "Software"), to
  // deal in the Software without restriction, including without limitation the
  // rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
  // sell copies of the Software, and to permit persons to whom the Software is
  // furnished to do so, subject to the following conditions:
  //
  // The above copyright notice and this permission notice shall be included in
  // all copies or substantial portions of the Software.
  //
  // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  // FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
  // IN THE SOFTWARE.
  //
  // Author: mierle@gmail.com (Keir Mierle)
  
  #ifndef LIBMV_AUTOTRACK_LISTENER_H_
  #define LIBMV_AUTOTRACK_LISTENER_H_
  
  namespace mv {
  
  struct OperationListener {
    // All hooks return true to continue or false to indicate the operation
    // should abort. Hooks should be thread safe (re-entrant).
    virtual bool Log(const string& message) = 0;
    virtual bool Progress(double fraction) = 0;
    virtual bool Cancelled() = 0;
  };
  
  }  // namespace mv
  
  #endif  // LIBMV_AUTOTRACK_LISTENER_H_
  