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       1                 :            : /***************************************************************************
       2                 :            :      qgsfeaturerenderergenerator.h
       3                 :            :      -----------------------
       4                 :            :     Date                 : December 2020
       5                 :            :     Copyright            : (C) 2020 by Nyall Dawson
       6                 :            :     Email                : nyall dot dawson 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 QGSFEATURERENDERERGENERATOR_H
      17                 :            : #define QGSFEATURERENDERERGENERATOR_H
      18                 :            : 
      19                 :            : #include "qgis_core.h"
      20                 :            : #include "qgis_sip.h"
      21                 :            : #include <QString>
      22                 :            : 
      23                 :            : class QgsFeatureRenderer;
      24                 :            : 
      25                 :            : /**
      26                 :            :  * \ingroup core
      27                 :            :  * \class QgsFeatureRendererGenerator
      28                 :            :  * \brief An interface for objects which generate feature renderers for vector layers.
      29                 :            :  * \since QGIS 3.18
      30                 :            :  */
      31                 :            : class CORE_EXPORT QgsFeatureRendererGenerator
      32                 :            : {
      33                 :            :   public:
      34                 :            : 
      35                 :          0 :     virtual ~QgsFeatureRendererGenerator() = default;
      36                 :            : 
      37                 :            :     /**
      38                 :            :      * Returns a unique ID string identifying the renderer generator.
      39                 :            :      */
      40                 :            :     virtual QString id() const = 0;
      41                 :            : 
      42                 :            :     /**
      43                 :            :      * Returns a double value which dictates the stacking or z order level associated with
      44                 :            :      * the returned renderer.
      45                 :            :      *
      46                 :            :      * A value > 0 will always be rendered AFTER the normal renderer for a vector layer (i.e. the
      47                 :            :      * renderer will be drawn on top of the normal feature renderer), while a value < 0 will always
      48                 :            :      * be rendered BEFORE the normal renderer (i.e. the rendered features will be drawn below the
      49                 :            :      * normal feature renderer).
      50                 :            :      *
      51                 :            :      * Since a layer may potentially have multiple extra renderers created by QgsFeatureRendererGenerator
      52                 :            :      * subclasses, the level will always be used to control the order that these renderers are drawn.
      53                 :            :      * A renderer with a lower level() return value will always be drawn before those with a higher level()
      54                 :            :      * value.
      55                 :            :      *
      56                 :            :      * The default implementation returns 1.0, i.e. features will be rendered ABOVE the normal
      57                 :            :      * vector layer renderer.
      58                 :            :      *
      59                 :            :      * \note If two QgsFeatureRendererGenerator implementations return the same level() value, then their
      60                 :            :      * ordering will be unpredictable.
      61                 :            :      */
      62                 :            :     virtual double level() const;
      63                 :            : 
      64                 :            :     /**
      65                 :            :      * Creates a new feature renderer to use when rendering a vector layer.
      66                 :            :      *
      67                 :            :      * Caller takes ownership of the returned renderer.
      68                 :            :      */
      69                 :            :     virtual QgsFeatureRenderer *createRenderer() const = 0 SIP_FACTORY;
      70                 :            : };
      71                 :            : 
      72                 :            : #endif // QGSFEATURERENDERERGENERATOR_H