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       1                 :            : /***************************************************************************
       2                 :            :   qgsfeedback.h
       3                 :            :   --------------------------------------
       4                 :            :   Date                 : July 2016
       5                 :            :   Copyright            : (C) 2016 by Martin Dobias
       6                 :            :   Email                : wonder dot sk at gmail dot com
       7                 :            :  ***************************************************************************
       8                 :            :  *                                                                         *
       9                 :            :  *   This program is free software; you can redistribute it and/or modify  *
      10                 :            :  *   it under the terms of the GNU General Public License as published by  *
      11                 :            :  *   the Free Software Foundation; either version 2 of the License, or     *
      12                 :            :  *   (at your option) any later version.                                   *
      13                 :            :  *                                                                         *
      14                 :            :  ***************************************************************************/
      15                 :            : 
      16                 :            : #ifndef QGSFEEDBACK_H
      17                 :            : #define QGSFEEDBACK_H
      18                 :            : 
      19                 :            : #include <QObject>
      20                 :            : 
      21                 :            : #include "qgis_core.h"
      22                 :            : #include "qgis_sip.h"
      23                 :            : 
      24                 :            : /**
      25                 :            :  * \ingroup core
      26                 :            :  * \brief Base class for feedback objects to be used for cancellation of something running in a worker thread.
      27                 :            :  *
      28                 :            :  * The class may be used as is or it may be subclassed for extended functionality
      29                 :            :  * for a particular operation (e.g. report progress or pass some data for preview).
      30                 :            :  *
      31                 :            :  * When cancel() is called, the internal code has two options to check for cancellation state:
      32                 :            :  *
      33                 :            :  * - if the worker thread uses an event loop (e.g. for network communication), the code can make a queued connection to canceled() signal and handle the cancellation in its slot.
      34                 :            :  * - if the worker thread does not use an event loop, it can poll isCanceled() method regularly to see if the operation should be canceled.
      35                 :            :  *
      36                 :            :  * The class is meant to be created and destroyed in the main thread.
      37                 :            :  *
      38                 :            :  * For map rendering, the object may be created in constructor of a QgsMapLayerRenderer
      39                 :            :  * subclass and available with QgsMapLayerRenderer::feedback() method. When a map rendering job
      40                 :            :  * gets canceled, the cancel() method is called on the feedback object of all layers.
      41                 :            :  *
      42                 :            :  * \since QGIS 3.0
      43                 :            :  */
      44                 :         25 : class CORE_EXPORT QgsFeedback : public QObject
      45                 :            : {
      46                 :            :     Q_OBJECT
      47                 :            :   public:
      48                 :            :     //! Construct a feedback object
      49                 :         25 :     QgsFeedback( QObject *parent SIP_TRANSFERTHIS = nullptr )
      50                 :         25 :       : QObject( parent )
      51                 :         75 :     {}
      52                 :            : 
      53                 :            :     //! Tells whether the operation has been canceled already
      54                 :        280 :     bool isCanceled() const { return mCanceled; }
      55                 :            : 
      56                 :            :     /**
      57                 :            :      * Sets the current progress for the feedback object. The \a progress
      58                 :            :      * argument is in percentage and valid values range from 0-100.
      59                 :            :      * \see progress()
      60                 :            :      * \see progressChanged()
      61                 :            :      * \since QGIS 3.0
      62                 :            :      */
      63                 :        496 :     void setProgress( double progress )
      64                 :            :     {
      65                 :            :       // avoid flooding with too many events
      66                 :        496 :       if ( static_cast< int >( mProgress * 10 ) != static_cast< int >( progress * 10 ) )
      67                 :        496 :         emit progressChanged( progress );
      68                 :            : 
      69                 :        496 :       mProgress = progress;
      70                 :        496 :     }
      71                 :            : 
      72                 :            :     /**
      73                 :            :      * Returns the current progress reported by the feedback object. Depending on how the
      74                 :            :      * feedback object is used progress reporting may not be supported. The returned value
      75                 :            :      * is in percentage and ranges from 0-100.
      76                 :            :      * \see setProgress()
      77                 :            :      * \see progressChanged()
      78                 :            :      * \since QGIS 3.0
      79                 :            :      */
      80                 :        496 :     double progress() const { return mProgress; }
      81                 :            : 
      82                 :            :   public slots:
      83                 :            : 
      84                 :            :     //! Tells the internal routines that the current operation should be canceled. This should be run by the main thread
      85                 :          0 :     void cancel()
      86                 :            :     {
      87                 :          0 :       if ( mCanceled )
      88                 :          0 :         return;  // only emit the signal once
      89                 :          0 :       mCanceled = true;
      90                 :          0 :       emit canceled();
      91                 :          0 :     }
      92                 :            : 
      93                 :            :   signals:
      94                 :            :     //! Internal routines can connect to this signal if they use event loop
      95                 :            :     void canceled();
      96                 :            : 
      97                 :            :     /**
      98                 :            :      * Emitted when the feedback object reports a progress change. Depending on how the
      99                 :            :      * feedback object is used progress reporting may not be supported. The \a progress
     100                 :            :      * argument is in percentage and ranges from 0-100.
     101                 :            :      * \see setProgress()
     102                 :            :      * \see progress()
     103                 :            :      * \since QGIS 3.0
     104                 :            :      */
     105                 :            :     void progressChanged( double progress );
     106                 :            : 
     107                 :            :   private:
     108                 :            :     //! Whether the operation has been canceled already. False by default.
     109                 :         25 :     bool mCanceled = false;
     110                 :            : 
     111                 :         25 :     double mProgress = 0.0;
     112                 :            : };
     113                 :            : 
     114                 :            : #endif // QGSFEEDBACK_H