Implement a registry for terrain objects

python/3d/3d_auto.sip

@@ -29,6 +29,7 @@
 %Include auto_generated/symbols/qgspoint3dsymbol.sip
 %Include auto_generated/symbols/qgspolygon3dsymbol.sip
 %Include auto_generated/symbols/qgspointcloud3dsymbol.sip
+%Include auto_generated/terrain/qgs3dterrainregistry.sip
 %Include auto_generated/terrain/qgsdemterrainsettings.sip
 %Include auto_generated/terrain/qgsflatterrainsettings.sip
 %Include auto_generated/terrain/qgsmeshterrainsettings.sip

python/3d/auto_additions/qgs3d.py

@@ -3,5 +3,6 @@ try:
     Qgs3D.instance = staticmethod(Qgs3D.instance)
     Qgs3D.initialize = staticmethod(Qgs3D.initialize)
     Qgs3D.materialRegistry = staticmethod(Qgs3D.materialRegistry)
+    Qgs3D.terrainRegistry = staticmethod(Qgs3D.terrainRegistry)
 except (NameError, AttributeError):
     pass

python/3d/auto_additions/qgs3dterrainregistry.py

@@ -0,0 +1,9 @@
+# The following has been generated automatically from src/3d/terrain/qgs3dterrainregistry.h
+try:
+    Qgs3DTerrainAbstractMetadata.__group__ = ['terrain']
+except (NameError, AttributeError):
+    pass
+try:
+    Qgs3DTerrainRegistry.__group__ = ['terrain']
+except (NameError, AttributeError):
+    pass

python/3d/auto_additions/qgsdemterrainsettings.py

@@ -1,5 +1,6 @@
 # The following has been generated automatically from src/3d/terrain/qgsdemterrainsettings.h
 try:
+    QgsDemTerrainSettings.create = staticmethod(QgsDemTerrainSettings.create)
     QgsDemTerrainSettings.__group__ = ['terrain']
 except (NameError, AttributeError):
     pass

python/3d/auto_additions/qgsflatterrainsettings.py

@@ -1,5 +1,6 @@
 # The following has been generated automatically from src/3d/terrain/qgsflatterrainsettings.h
 try:
+    QgsFlatTerrainSettings.create = staticmethod(QgsFlatTerrainSettings.create)
     QgsFlatTerrainSettings.__group__ = ['terrain']
 except (NameError, AttributeError):
     pass

python/3d/auto_additions/qgsmeshterrainsettings.py

@@ -1,5 +1,6 @@
 # The following has been generated automatically from src/3d/terrain/qgsmeshterrainsettings.h
 try:
+    QgsMeshTerrainSettings.create = staticmethod(QgsMeshTerrainSettings.create)
     QgsMeshTerrainSettings.__group__ = ['terrain']
 except (NameError, AttributeError):
     pass

python/3d/auto_generated/qgs3d.sip.in

@@ -39,6 +39,11 @@ Initializes the 3D framework.
     static QgsMaterialRegistry *materialRegistry();
 %Docstring
 Returns the material registry, used for managing 3D materials.
+%End
+
+    static Qgs3DTerrainRegistry *terrainRegistry();
+%Docstring
+Returns the terrain registry, used for managing 3D terrains.
 %End
 
   private:

python/3d/auto_generated/terrain/qgs3dterrainregistry.sip.in

@@ -0,0 +1,120 @@
+/************************************************************************
+ * This file has been generated automatically from                      *
+ *                                                                      *
+ * src/3d/terrain/qgs3dterrainregistry.h                                *
+ *                                                                      *
+ * Do not edit manually ! Edit header and run scripts/sipify.py again   *
+ ************************************************************************/
+
+
+
+
+
+class Qgs3DTerrainAbstractMetadata
+{
+%Docstring(signature="appended")
+Stores metadata about one 3D terrain class.
+
+.. note::
+
+   It's necessary to implement :py:func:`~createTerrainSettings` function.
+   In C++ you can use Qgs3DTerrainMetadata convenience class.
+
+.. versionadded:: 3.42
+%End
+
+%TypeHeaderCode
+#include "qgs3dterrainregistry.h"
+%End
+  public:
+    Qgs3DTerrainAbstractMetadata( const QString &type, const QString &visibleName, const QIcon &icon = QIcon() );
+%Docstring
+Constructor for Qgs3DTerrainAbstractMetadata, with the specified ``type`` and ``visibleName``.
+
+An optional ``icon`` can be specified to represent the material type.
+%End
+
+    virtual ~Qgs3DTerrainAbstractMetadata();
+
+    QString type() const;
+%Docstring
+Returns the unique terrain type string.
+%End
+
+    QString visibleName() const;
+%Docstring
+Returns the terrain's visible (translated) name.
+%End
+
+    QIcon icon() const;
+%Docstring
+Returns an icon representing the terrain type, if available.
+%End
+
+    virtual QgsAbstractTerrainSettings *createTerrainSettings() = 0 /Factory/;
+%Docstring
+Creates a new instance of this terrain settings type.
+
+Caller takes ownership of the returned object.
+%End
+
+};
+
+
+
+
+class Qgs3DTerrainRegistry
+{
+%Docstring(signature="appended")
+Registry of available 3d terrain classes.
+
+Qgs3DTerrainRegistry is not usually directly created, but rather accessed through
+Qgs3D.terrainRegistry().
+
+.. versionadded:: 3.42
+%End
+
+%TypeHeaderCode
+#include "qgs3dterrainregistry.h"
+%End
+  public:
+    Qgs3DTerrainRegistry();
+    ~Qgs3DTerrainRegistry();
+
+
+    Qgs3DTerrainAbstractMetadata *terrainMetadata( const QString &type ) const;
+%Docstring
+Returns metadata for specified terrain ``type``. Returns ``None`` if not found
+%End
+
+    QStringList types() const;
+%Docstring
+Returns a list of all available terrain types.
+%End
+
+    bool addType( Qgs3DTerrainAbstractMetadata *metadata /Transfer/ );
+%Docstring
+Registers a new terrain type. Takes ownership of the ``metadata`` instance.
+%End
+
+    QgsAbstractTerrainSettings *createTerrainSettings( const QString &type ) const /Factory/;
+%Docstring
+Creates a new instance of the terrain settings of the specified ``type``.
+
+The caller takes ownership of the returned object.
+
+Returns ``None`` if the specified type is not found in the registry.
+%End
+
+  private:
+    Qgs3DTerrainRegistry( const Qgs3DTerrainRegistry &rh );
+};
+
+
+/************************************************************************
+ * This file has been generated automatically from                      *
+ *                                                                      *
+ * src/3d/terrain/qgs3dterrainregistry.h                                *
+ *                                                                      *
+ * Do not edit manually ! Edit header and run scripts/sipify.py again   *
+ ************************************************************************/

python/3d/auto_generated/terrain/qgsdemterrainsettings.sip.in

@@ -26,6 +26,11 @@ Terrain settings for a terrain generator that uses a raster DEM layer to build t
 #include "qgsdemterrainsettings.h"
 %End
   public:
+    static QgsAbstractTerrainSettings *create() /Factory/;
+%Docstring
+Creates a new instance of a QgsDemTerrainSettings object.
+%End
+
     QgsDemTerrainSettings *clone() const final /Factory/;
     QString type() const final;
     void readXml( const QDomElement &element, const QgsReadWriteContext &context ) final;

python/3d/auto_generated/terrain/qgsflatterrainsettings.sip.in

@@ -26,6 +26,11 @@ Terrain settings for a simple flat area terrain.
 #include "qgsflatterrainsettings.h"
 %End
   public:
+    static QgsAbstractTerrainSettings *create() /Factory/;
+%Docstring
+Creates a new instance of a QgsFlatTerrainSettings object.
+%End
+
     QgsFlatTerrainSettings *clone() const final /Factory/;
     QString type() const final;
     void readXml( const QDomElement &element, const QgsReadWriteContext &context ) final;

python/3d/auto_generated/terrain/qgsmeshterrainsettings.sip.in

@@ -26,6 +26,11 @@ Terrain settings for a terrain generator that uses uses the Z values of a mesh l
 #include "qgsmeshterrainsettings.h"
 %End
   public:
+    static QgsAbstractTerrainSettings *create() /Factory/;
+%Docstring
+Creates a new instance of a QgsMeshTerrainSettings object.
+%End
+
     QgsMeshTerrainSettings *clone() const final /Factory/;
     QString type() const final;
     void readXml( const QDomElement &element, const QgsReadWriteContext &context ) final;

python/PyQt6/3d/3d_auto.sip

@@ -29,6 +29,7 @@
 %Include auto_generated/symbols/qgspoint3dsymbol.sip
 %Include auto_generated/symbols/qgspolygon3dsymbol.sip
 %Include auto_generated/symbols/qgspointcloud3dsymbol.sip
+%Include auto_generated/terrain/qgs3dterrainregistry.sip
 %Include auto_generated/terrain/qgsdemterrainsettings.sip
 %Include auto_generated/terrain/qgsflatterrainsettings.sip
 %Include auto_generated/terrain/qgsmeshterrainsettings.sip

python/PyQt6/3d/auto_additions/qgs3d.py

@@ -3,5 +3,6 @@ try:
     Qgs3D.instance = staticmethod(Qgs3D.instance)
     Qgs3D.initialize = staticmethod(Qgs3D.initialize)
     Qgs3D.materialRegistry = staticmethod(Qgs3D.materialRegistry)
+    Qgs3D.terrainRegistry = staticmethod(Qgs3D.terrainRegistry)
 except (NameError, AttributeError):
     pass

python/PyQt6/3d/auto_additions/qgs3dterrainregistry.py

@@ -0,0 +1,9 @@
+# The following has been generated automatically from src/3d/terrain/qgs3dterrainregistry.h
+try:
+    Qgs3DTerrainAbstractMetadata.__group__ = ['terrain']
+except (NameError, AttributeError):
+    pass
+try:
+    Qgs3DTerrainRegistry.__group__ = ['terrain']
+except (NameError, AttributeError):
+    pass

python/PyQt6/3d/auto_additions/qgsdemterrainsettings.py

@@ -1,5 +1,6 @@
 # The following has been generated automatically from src/3d/terrain/qgsdemterrainsettings.h
 try:
+    QgsDemTerrainSettings.create = staticmethod(QgsDemTerrainSettings.create)
     QgsDemTerrainSettings.__group__ = ['terrain']
 except (NameError, AttributeError):
     pass

python/PyQt6/3d/auto_additions/qgsflatterrainsettings.py

@@ -1,5 +1,6 @@
 # The following has been generated automatically from src/3d/terrain/qgsflatterrainsettings.h
 try:
+    QgsFlatTerrainSettings.create = staticmethod(QgsFlatTerrainSettings.create)
     QgsFlatTerrainSettings.__group__ = ['terrain']
 except (NameError, AttributeError):
     pass

python/PyQt6/3d/auto_additions/qgsmeshterrainsettings.py

@@ -1,5 +1,6 @@
 # The following has been generated automatically from src/3d/terrain/qgsmeshterrainsettings.h
 try:
+    QgsMeshTerrainSettings.create = staticmethod(QgsMeshTerrainSettings.create)
     QgsMeshTerrainSettings.__group__ = ['terrain']
 except (NameError, AttributeError):
     pass

python/PyQt6/3d/auto_generated/qgs3d.sip.in

@@ -39,6 +39,11 @@ Initializes the 3D framework.
     static QgsMaterialRegistry *materialRegistry();
 %Docstring
 Returns the material registry, used for managing 3D materials.
+%End
+
+    static Qgs3DTerrainRegistry *terrainRegistry();
+%Docstring
+Returns the terrain registry, used for managing 3D terrains.
 %End
 
   private:

python/PyQt6/3d/auto_generated/terrain/qgs3dterrainregistry.sip.in

@@ -0,0 +1,120 @@
+/************************************************************************
+ * This file has been generated automatically from                      *
+ *                                                                      *
+ * src/3d/terrain/qgs3dterrainregistry.h                                *
+ *                                                                      *
+ * Do not edit manually ! Edit header and run scripts/sipify.py again   *
+ ************************************************************************/
+
+
+
+
+
+class Qgs3DTerrainAbstractMetadata
+{
+%Docstring(signature="appended")
+Stores metadata about one 3D terrain class.
+
+.. note::
+
+   It's necessary to implement :py:func:`~createTerrainSettings` function.
+   In C++ you can use Qgs3DTerrainMetadata convenience class.
+
+.. versionadded:: 3.42
+%End
+
+%TypeHeaderCode
+#include "qgs3dterrainregistry.h"
+%End
+  public:
+    Qgs3DTerrainAbstractMetadata( const QString &type, const QString &visibleName, const QIcon &icon = QIcon() );
+%Docstring
+Constructor for Qgs3DTerrainAbstractMetadata, with the specified ``type`` and ``visibleName``.
+
+An optional ``icon`` can be specified to represent the material type.
+%End
+
+    virtual ~Qgs3DTerrainAbstractMetadata();
+
+    QString type() const;
+%Docstring
+Returns the unique terrain type string.
+%End
+
+    QString visibleName() const;
+%Docstring
+Returns the terrain's visible (translated) name.
+%End
+
+    QIcon icon() const;
+%Docstring
+Returns an icon representing the terrain type, if available.
+%End
+
+    virtual QgsAbstractTerrainSettings *createTerrainSettings() = 0 /Factory/;
+%Docstring
+Creates a new instance of this terrain settings type.
+
+Caller takes ownership of the returned object.
+%End
+
+};
+
+
+
+
+class Qgs3DTerrainRegistry
+{
+%Docstring(signature="appended")
+Registry of available 3d terrain classes.
+
+Qgs3DTerrainRegistry is not usually directly created, but rather accessed through
+Qgs3D.terrainRegistry().
+
+.. versionadded:: 3.42
+%End
+
+%TypeHeaderCode
+#include "qgs3dterrainregistry.h"
+%End
+  public:
+    Qgs3DTerrainRegistry();
+    ~Qgs3DTerrainRegistry();
+
+
+    Qgs3DTerrainAbstractMetadata *terrainMetadata( const QString &type ) const;
+%Docstring
+Returns metadata for specified terrain ``type``. Returns ``None`` if not found
+%End
+
+    QStringList types() const;
+%Docstring
+Returns a list of all available terrain types.
+%End
+
+    bool addType( Qgs3DTerrainAbstractMetadata *metadata /Transfer/ );
+%Docstring
+Registers a new terrain type. Takes ownership of the ``metadata`` instance.
+%End
+
+    QgsAbstractTerrainSettings *createTerrainSettings( const QString &type ) const /Factory/;
+%Docstring
+Creates a new instance of the terrain settings of the specified ``type``.
+
+The caller takes ownership of the returned object.
+
+Returns ``None`` if the specified type is not found in the registry.
+%End
+
+  private:
+    Qgs3DTerrainRegistry( const Qgs3DTerrainRegistry &rh );
+};
+
+
+/************************************************************************
+ * This file has been generated automatically from                      *
+ *                                                                      *
+ * src/3d/terrain/qgs3dterrainregistry.h                                *
+ *                                                                      *
+ * Do not edit manually ! Edit header and run scripts/sipify.py again   *
+ ************************************************************************/

python/PyQt6/3d/auto_generated/terrain/qgsdemterrainsettings.sip.in

@@ -26,6 +26,11 @@ Terrain settings for a terrain generator that uses a raster DEM layer to build t
 #include "qgsdemterrainsettings.h"
 %End
   public:
+    static QgsAbstractTerrainSettings *create() /Factory/;
+%Docstring
+Creates a new instance of a QgsDemTerrainSettings object.
+%End
+
     QgsDemTerrainSettings *clone() const final /Factory/;
     QString type() const final;
     void readXml( const QDomElement &element, const QgsReadWriteContext &context ) final;

python/PyQt6/3d/auto_generated/terrain/qgsflatterrainsettings.sip.in

@@ -26,6 +26,11 @@ Terrain settings for a simple flat area terrain.
 #include "qgsflatterrainsettings.h"
 %End
   public:
+    static QgsAbstractTerrainSettings *create() /Factory/;
+%Docstring
+Creates a new instance of a QgsFlatTerrainSettings object.
+%End
+
     QgsFlatTerrainSettings *clone() const final /Factory/;
     QString type() const final;
     void readXml( const QDomElement &element, const QgsReadWriteContext &context ) final;

python/PyQt6/3d/auto_generated/terrain/qgsmeshterrainsettings.sip.in

@@ -26,6 +26,11 @@ Terrain settings for a terrain generator that uses uses the Z values of a mesh l
 #include "qgsmeshterrainsettings.h"
 %End
   public:
+    static QgsAbstractTerrainSettings *create() /Factory/;
+%Docstring
+Creates a new instance of a QgsMeshTerrainSettings object.
+%End
+
     QgsMeshTerrainSettings *clone() const final /Factory/;
     QString type() const final;
     void readXml( const QDomElement &element, const QgsReadWriteContext &context ) final;

src/3d/CMakeLists.txt

@@ -97,6 +97,7 @@ set(QGIS_3D_SRCS
   symbols/qgspointcloud3dsymbol.cpp
   symbols/qgspointcloud3dsymbol_p.cpp
 
+  terrain/qgs3dterrainregistry.cpp
   terrain/qgsdemterraingenerator.cpp
   terrain/qgsdemterrainsettings.cpp
   terrain/qgsdemterraintilegeometry_p.cpp
@@ -192,6 +193,7 @@ set(QGIS_3D_HDRS
   symbols/qgspolygon3dsymbol.h
   symbols/qgspointcloud3dsymbol.h
 
+  terrain/qgs3dterrainregistry.h
   terrain/qgsdemterraingenerator.h
   terrain/qgsdemterrainsettings.h
   terrain/qgsflatterraingenerator.h

src/3d/qgs3d.cpp

@@ -42,6 +42,8 @@
 #include "qgsphongtexturedmaterialsettings.h"
 #include "qgsnullmaterialsettings.h"
 
+#include "qgs3dterrainregistry.h"
+
 #include "qgsstyle.h"
 
 Qgs3D *Qgs3D::instance()
@@ -88,7 +90,13 @@ QgsMaterialRegistry *Qgs3D::materialRegistry()
   return instance()->mMaterialRegistry;
 }
 
+Qgs3DTerrainRegistry *Qgs3D::terrainRegistry()
+{
+  return instance()->mTerrainRegistry;
+}
+
 Qgs3D::Qgs3D()
 {
   mMaterialRegistry = new QgsMaterialRegistry();
+  mTerrainRegistry = new Qgs3DTerrainRegistry();
 }

src/3d/qgs3d.h

@@ -22,6 +22,7 @@
 #include "qgis_sip.h"
 
 class QgsMaterialRegistry;
+class Qgs3DTerrainRegistry;
 
 /**
  * \ingroup gui
@@ -52,6 +53,11 @@ class _3D_EXPORT Qgs3D
      */
     static QgsMaterialRegistry *materialRegistry();
 
+    /**
+     * Returns the terrain registry, used for managing 3D terrains.
+     */
+    static Qgs3DTerrainRegistry *terrainRegistry();
+
   private:
     Qgs3D();
 
@@ -62,6 +68,7 @@ class _3D_EXPORT Qgs3D
     bool mInitialized = false;
 
     QgsMaterialRegistry *mMaterialRegistry = nullptr;
+    Qgs3DTerrainRegistry *mTerrainRegistry = nullptr;
 };
 
 #endif // QGS3D_H

src/3d/qgs3dmapsettings.cpp

@@ -16,6 +16,7 @@
 #include "qgs3dmapsettings.h"
 #include "moc_qgs3dmapsettings.cpp"
 
+#include "qgs3d.h"
 #include "qgs3dutils.h"
 #include "qgsflatterraingenerator.h"
 #include "qgsdemterraingenerator.h"
@@ -35,6 +36,7 @@
 #include "qgsmaplayerlistutils_p.h"
 #include "qgsterrainsettings.h"
 #include "qgsflatterrainsettings.h"
+#include "qgs3dterrainregistry.h"
 
 #include <QDomDocument>
 #include <QDomElement>
@@ -272,6 +274,14 @@ void Qgs3DMapSettings::readXml( const QDomElement &elem, const QgsReadWriteConte
     flatGen->setCrs( mCrs );
     setTerrainGenerator( flatGen );
   }
+
+  std::unique_ptr<QgsAbstractTerrainSettings> terrainSettings( Qgs3D::terrainRegistry()->createTerrainSettings( terrainGenType ) );
+  if ( terrainSettings )
+  {
+    terrainSettings->readXml( elemTerrainGenerator, context );
+    setTerrainSettings( terrainSettings.release() );
+  }
+
   mTerrainGenerator->readXml( elemTerrainGenerator );
 
   QDomElement elemSkybox = elem.firstChildElement( QStringLiteral( "skybox" ) );

src/3d/terrain/qgs3dterrainregistry.cpp

@@ -0,0 +1,70 @@
+/***************************************************************************
+  qgs3dterrainregistry.cpp
+  --------------------------------------
+  Date                 : November 2024
+  Copyright            : (C) 2024 by Nyall Dawson
+  Email                : nyall dot dawson at gmail dot com
+ ***************************************************************************
+ *                                                                         *
+ *   This program is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU General Public License as published by  *
+ *   the Free Software Foundation; either version 2 of the License, or     *
+ *   (at your option) any later version.                                   *
+ *                                                                         *
+ ***************************************************************************/
+
+#include "qgs3dterrainregistry.h"
+#include "qgis.h"
+
+#include "qgsflatterrainsettings.h"
+#include "qgsdemterrainsettings.h"
+#include "qgsmeshterrainsettings.h"
+
+#include <QDomElement>
+
+
+Qgs3DTerrainRegistry::Qgs3DTerrainRegistry()
+{
+  addType( new Qgs3DTerrainMetadata( QStringLiteral( "flat" ), QObject::tr( "Flat Terrain" ), &QgsFlatTerrainSettings::create ) );
+  addType( new Qgs3DTerrainMetadata( QStringLiteral( "dem" ), QObject::tr( "DEM (Raster Layer)" ), &QgsDemTerrainSettings::create ) );
+  addType( new Qgs3DTerrainMetadata( QStringLiteral( "mesh" ), QObject::tr( "Mesh" ), &QgsMeshTerrainSettings::create ) );
+}
+
+Qgs3DTerrainRegistry::~Qgs3DTerrainRegistry()
+{
+  qDeleteAll( mMetadata );
+}
+
+bool Qgs3DTerrainRegistry::addType( Qgs3DTerrainAbstractMetadata *metadata )
+{
+  if ( !metadata || mMetadata.contains( metadata->type() ) )
+    return false;
+
+  mMetadata[metadata->type()] = metadata;
+  mTerrainOrder << metadata->type();
+  return true;
+}
+
+QgsAbstractTerrainSettings *Qgs3DTerrainRegistry::createTerrainSettings( const QString &type ) const
+{
+  if ( !mMetadata.contains( type ) )
+    return nullptr;
+
+  return mMetadata[type]->createTerrainSettings();
+}
+
+Qgs3DTerrainAbstractMetadata *Qgs3DTerrainRegistry::terrainMetadata( const QString &type ) const
+{
+  return mMetadata.value( type );
+}
+
+QStringList Qgs3DTerrainRegistry::types() const
+{
+  QStringList types;
+  for ( const QString &type : mTerrainOrder )
+  {
+    if ( mMetadata.value( type ) )
+      types << type;
+  }
+  return types;
+}

src/3d/terrain/qgs3dterrainregistry.h

@@ -0,0 +1,174 @@
+/***************************************************************************
+  qgs3dterrainregistry.h
+  --------------------------------------
+  Date                 : November 2024
+  Copyright            : (C) 2024 by Nyall Dawson
+  Email                : nyall dot dawson at gmail dot com
+ ***************************************************************************
+ *                                                                         *
+ *   This program is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU General Public License as published by  *
+ *   the Free Software Foundation; either version 2 of the License, or     *
+ *   (at your option) any later version.                                   *
+ *                                                                         *
+ ***************************************************************************/
+
+#ifndef QGS3DTERRAINREGISTRY_H
+#define QGS3DTERRAINREGISTRY_H
+
+#include "qgis_3d.h"
+#include "qgis_sip.h"
+#include <QString>
+
+#include <QDomElement>
+#include <QMap>
+#include <QIcon>
+
+class QgsReadWriteContext;
+class QgsAbstractTerrainSettings;
+
+/**
+ * \ingroup core
+ * \brief Stores metadata about one 3D terrain class.
+ *
+ * \note It's necessary to implement createTerrainSettings() function.
+ * In C++ you can use Qgs3DTerrainMetadata convenience class.
+ *
+ * \since QGIS 3.42
+ */
+class _3D_EXPORT Qgs3DTerrainAbstractMetadata
+{
+  public:
+    /**
+     * Constructor for Qgs3DTerrainAbstractMetadata, with the specified \a type and \a visibleName.
+     *
+     * An optional \a icon can be specified to represent the material type.
+     */
+    Qgs3DTerrainAbstractMetadata( const QString &type, const QString &visibleName, const QIcon &icon = QIcon() )
+      : mType( type )
+      , mVisibleName( visibleName )
+      , mIcon( icon )
+    {}
+
+    virtual ~Qgs3DTerrainAbstractMetadata() = default;
+
+    /**
+     * Returns the unique terrain type string.
+     */
+    QString type() const { return mType; }
+
+    /**
+     * Returns the terrain's visible (translated) name.
+     */
+    QString visibleName() const { return mVisibleName; }
+
+    /**
+     * Returns an icon representing the terrain type, if available.
+     */
+    QIcon icon() const { return mIcon; }
+
+    /**
+     * Creates a new instance of this terrain settings type.
+     *
+     * Caller takes ownership of the returned object.
+     */
+    virtual QgsAbstractTerrainSettings *createTerrainSettings() = 0 SIP_FACTORY;
+
+  private:
+    QString mType;
+    QString mVisibleName;
+    QIcon mIcon;
+};
+
+//! Terrain settings creation function
+typedef QgsAbstractTerrainSettings *( *QgsTerrainSettingsCreateFunc )() SIP_SKIP;
+
+#ifndef SIP_RUN
+
+/**
+ * \ingroup core
+ * \brief Convenience metadata class that uses static functions to create 3D terrain objects.
+ *
+ * \note Not available in Python bindings.
+ *
+ * \since QGIS 3.42
+ */
+class _3D_EXPORT Qgs3DTerrainMetadata : public Qgs3DTerrainAbstractMetadata
+{
+  public:
+    /**
+     * Constructor for Qgs3DTerrainMetadata, with the specified \a type and \a visibleName.
+     *
+     * The \a pfCreate argument is used to specify
+     * a static function for creating the terrain settings.
+     *
+     * An optional \a icon can be specified to represent the terrain type.
+     */
+    Qgs3DTerrainMetadata( const QString &type, const QString &visibleName, QgsTerrainSettingsCreateFunc pfCreate, const QIcon &icon = QIcon() )
+      : Qgs3DTerrainAbstractMetadata( type, visibleName, icon )
+      , mCreateFunc( pfCreate )
+    {}
+
+    /**
+     * Returns the terrain setting's creation function.
+     */
+    QgsTerrainSettingsCreateFunc createFunction() const { return mCreateFunc; }
+
+    QgsAbstractTerrainSettings *createTerrainSettings() override SIP_FACTORY { return mCreateFunc ? mCreateFunc() : nullptr; }
+
+  private:
+    QgsTerrainSettingsCreateFunc mCreateFunc;
+};
+#endif
+
+
+/**
+ * \ingroup core
+ * \brief Registry of available 3d terrain classes.
+ *
+ * Qgs3DTerrainRegistry is not usually directly created, but rather accessed through
+ * Qgs3D::terrainRegistry().
+ *
+ * \since QGIS 3.42
+ */
+class _3D_EXPORT Qgs3DTerrainRegistry
+{
+  public:
+    Qgs3DTerrainRegistry();
+    ~Qgs3DTerrainRegistry();
+
+    Qgs3DTerrainRegistry( const Qgs3DTerrainRegistry &rh ) = delete;
+    Qgs3DTerrainRegistry &operator=( const Qgs3DTerrainRegistry &rh ) = delete;
+
+    //! Returns metadata for specified terrain \a type. Returns NULLPTR if not found
+    Qgs3DTerrainAbstractMetadata *terrainMetadata( const QString &type ) const;
+
+    /**
+     * Returns a list of all available terrain types.
+     */
+    QStringList types() const;
+
+    //! Registers a new terrain type. Takes ownership of the \a metadata instance.
+    bool addType( Qgs3DTerrainAbstractMetadata *metadata SIP_TRANSFER );
+
+    /**
+     * Creates a new instance of the terrain settings of the specified \a type.
+     *
+     * The caller takes ownership of the returned object.
+     *
+     * Returns NULLPTR if the specified type is not found in the registry.
+     */
+    QgsAbstractTerrainSettings *createTerrainSettings( const QString &type ) const SIP_FACTORY;
+
+  private:
+#ifdef SIP_RUN
+    Qgs3DTerrainRegistry( const Qgs3DTerrainRegistry &rh );
+#endif
+
+    QMap<QString, Qgs3DTerrainAbstractMetadata *> mMetadata;
+    //! List of terrains, maintained in the order that they have been added
+    QStringList mTerrainOrder;
+};
+
+
+#endif // QGS3DTERRAINREGISTRY_H

src/3d/terrain/qgsdemterrainsettings.cpp

@@ -16,6 +16,11 @@
 #include "qgsdemterrainsettings.h"
 #include "qgsrasterlayer.h"
 
+QgsAbstractTerrainSettings *QgsDemTerrainSettings::create()
+{
+  return new QgsDemTerrainSettings();
+}
+
 QgsDemTerrainSettings *QgsDemTerrainSettings::clone() const
 {
   return new QgsDemTerrainSettings( *this );

src/3d/terrain/qgsdemterrainsettings.h

@@ -35,6 +35,11 @@ class QgsRasterLayer;
 class _3D_EXPORT QgsDemTerrainSettings : public QgsAbstractTerrainSettings
 {
   public:
+    /**
+     * Creates a new instance of a QgsDemTerrainSettings object.
+     */
+    static QgsAbstractTerrainSettings *create() SIP_FACTORY;
+
     QgsDemTerrainSettings *clone() const final SIP_FACTORY;
     QString type() const final;
     void readXml( const QDomElement &element, const QgsReadWriteContext &context ) final;

src/3d/terrain/qgsflatterrainsettings.cpp

@@ -15,6 +15,11 @@
 
 #include "qgsflatterrainsettings.h"
 
+QgsAbstractTerrainSettings *QgsFlatTerrainSettings::create()
+{
+  return new QgsFlatTerrainSettings();
+}
+
 QgsFlatTerrainSettings *QgsFlatTerrainSettings::clone() const
 {
   return new QgsFlatTerrainSettings( *this );

src/3d/terrain/qgsflatterrainsettings.h

@@ -36,6 +36,11 @@ class QgsProject;
 class _3D_EXPORT QgsFlatTerrainSettings : public QgsAbstractTerrainSettings
 {
   public:
+    /**
+     * Creates a new instance of a QgsFlatTerrainSettings object.
+     */
+    static QgsAbstractTerrainSettings *create() SIP_FACTORY;
+
     QgsFlatTerrainSettings *clone() const final SIP_FACTORY;
     QString type() const final;
     void readXml( const QDomElement &element, const QgsReadWriteContext &context ) final;

src/3d/terrain/qgsmeshterrainsettings.cpp

@@ -16,6 +16,11 @@
 #include "qgsmeshterrainsettings.h"
 #include "qgsmeshlayer.h"
 
+QgsAbstractTerrainSettings *QgsMeshTerrainSettings::create()
+{
+  return new QgsMeshTerrainSettings();
+}
+
 QgsMeshTerrainSettings *QgsMeshTerrainSettings::clone() const
 {
   return new QgsMeshTerrainSettings( *this );

src/3d/terrain/qgsmeshterrainsettings.h

@@ -38,6 +38,11 @@ class QgsMeshLayer;
 class _3D_EXPORT QgsMeshTerrainSettings : public QgsAbstractTerrainSettings
 {
   public:
+    /**
+     * Creates a new instance of a QgsMeshTerrainSettings object.
+     */
+    static QgsAbstractTerrainSettings *create() SIP_FACTORY;
+
     QgsMeshTerrainSettings *clone() const final SIP_FACTORY;
     QString type() const final;
     void readXml( const QDomElement &element, const QgsReadWriteContext &context ) final;

tests/src/python/CMakeLists.txt

@@ -535,6 +535,7 @@ endif()
 
 if (WITH_3D)
   ADD_PYTHON_TEST(PyQgs3DMaterials test_qgs3dmaterials.py)
+  ADD_PYTHON_TEST(PyQgs3DTerrain test_qgs3dterrain.py)
   ADD_PYTHON_TEST(PyQgsMesh3DSymbol test_qgsmesh3dsymbol.py)
 endif()
 

tests/src/python/test_qgs3dterrain.py

@@ -0,0 +1,295 @@
+"""QGIS Unit tests for 3D terrrain objects.
+
+.. note:: This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2 of the License, or
+(at your option) any later version.
+"""
+
+from qgis.PyQt.QtXml import (
+    QDomDocument,
+)
+from qgis.core import QgsProject, QgsRasterLayer, QgsMeshLayer, QgsReadWriteContext
+from qgis._3d import (
+    QgsFlatTerrainSettings,
+    QgsDemTerrainSettings,
+    QgsMeshTerrainSettings,
+    Qgs3DTerrainRegistry,
+)
+import unittest
+from qgis.testing import start_app, QgisTestCase
+
+from utilities import unitTestDataPath
+
+start_app()
+TEST_DATA_DIR = unitTestDataPath()
+
+
+class TestQgs3DTerrain(QgisTestCase):
+
+    def test_flat_terrain(self):
+        settings = QgsFlatTerrainSettings.create()
+        self.assertIsInstance(settings, QgsFlatTerrainSettings)
+
+        self.assertEqual(settings.verticalScale(), 1)
+        settings.setVerticalScale(3)
+        self.assertEqual(settings.verticalScale(), 3)
+
+        self.assertEqual(settings.mapTileResolution(), 512)
+        settings.setMapTileResolution(36)
+        self.assertEqual(settings.mapTileResolution(), 36)
+
+        self.assertEqual(settings.maximumScreenError(), 3.0)
+        settings.setMaximumScreenError(4.5)
+        self.assertEqual(settings.maximumScreenError(), 4.5)
+
+        self.assertEqual(settings.maximumGroundError(), 1)
+        settings.setMaximumGroundError(14.5)
+        self.assertEqual(settings.maximumGroundError(), 14.5)
+
+        self.assertEqual(settings.elevationOffset(), 0)
+        settings.setElevationOffset(24.5)
+        self.assertEqual(settings.elevationOffset(), 24.5)
+
+        # clone
+        settings2 = settings.clone()
+        self.assertEqual(settings2.verticalScale(), 3)
+        self.assertEqual(settings2.mapTileResolution(), 36)
+        self.assertEqual(settings2.maximumScreenError(), 4.5)
+        self.assertEqual(settings2.maximumGroundError(), 14.5)
+        self.assertEqual(settings2.elevationOffset(), 24.5)
+        self.assertTrue(settings2.equals(settings))
+
+        # equals
+        settings2.setVerticalScale(4)
+        self.assertFalse(settings2.equals(settings))
+        settings2 = settings.clone()
+        settings2.setMapTileResolution(136)
+        self.assertFalse(settings2.equals(settings))
+        settings2 = settings.clone()
+        settings2.setMaximumScreenError(136)
+        self.assertFalse(settings2.equals(settings))
+        settings2 = settings.clone()
+        settings2.setMaximumGroundError(136)
+        self.assertFalse(settings2.equals(settings))
+        settings2 = settings.clone()
+        settings2.setElevationOffset(136)
+        self.assertFalse(settings2.equals(settings))
+
+        # read/write xml
+        doc = QDomDocument("testdoc")
+        elem = doc.createElement("test")
+        settings.writeXml(elem, QgsReadWriteContext())
+
+        settings3 = QgsFlatTerrainSettings()
+        settings3.readXml(elem, QgsReadWriteContext())
+        self.assertEqual(settings3.verticalScale(), 3)
+        self.assertEqual(settings3.mapTileResolution(), 36)
+        self.assertEqual(settings3.maximumScreenError(), 4.5)
+        self.assertEqual(settings3.maximumGroundError(), 14.5)
+        self.assertEqual(settings3.elevationOffset(), 24.5)
+
+    def test_dem_terrain(self):
+        p = QgsProject()
+        rl = QgsRasterLayer(
+            self.get_test_data_path("raster/dem.tif").as_posix(), "layer1"
+        )
+        self.assertTrue(rl.isValid())
+        rl2 = QgsRasterLayer(
+            self.get_test_data_path("raster/dem.tif").as_posix(), "layer2"
+        )
+        self.assertTrue(rl2.isValid())
+        p.addMapLayer(rl)
+        p.addMapLayer(rl2)
+
+        settings = QgsDemTerrainSettings.create()
+        self.assertIsInstance(settings, QgsDemTerrainSettings)
+
+        settings.setLayer(rl)
+        self.assertEqual(settings.layer(), rl)
+
+        self.assertEqual(settings.resolution(), 16)
+        settings.setResolution(66)
+        self.assertEqual(settings.resolution(), 66)
+
+        self.assertEqual(settings.skirtHeight(), 10)
+        settings.setSkirtHeight(366)
+        self.assertEqual(settings.skirtHeight(), 366)
+
+        self.assertEqual(settings.verticalScale(), 1)
+        settings.setVerticalScale(3)
+        self.assertEqual(settings.verticalScale(), 3)
+
+        self.assertEqual(settings.mapTileResolution(), 512)
+        settings.setMapTileResolution(36)
+        self.assertEqual(settings.mapTileResolution(), 36)
+
+        self.assertEqual(settings.maximumScreenError(), 3.0)
+        settings.setMaximumScreenError(4.5)
+        self.assertEqual(settings.maximumScreenError(), 4.5)
+
+        self.assertEqual(settings.maximumGroundError(), 1)
+        settings.setMaximumGroundError(14.5)
+        self.assertEqual(settings.maximumGroundError(), 14.5)
+
+        self.assertEqual(settings.elevationOffset(), 0)
+        settings.setElevationOffset(24.5)
+        self.assertEqual(settings.elevationOffset(), 24.5)
+
+        # clone
+        settings2 = settings.clone()
+        self.assertEqual(settings2.layer(), rl)
+        self.assertEqual(settings2.resolution(), 66)
+        self.assertEqual(settings2.skirtHeight(), 366)
+        self.assertEqual(settings2.verticalScale(), 3)
+        self.assertEqual(settings2.mapTileResolution(), 36)
+        self.assertEqual(settings2.maximumScreenError(), 4.5)
+        self.assertEqual(settings2.maximumGroundError(), 14.5)
+        self.assertEqual(settings2.elevationOffset(), 24.5)
+        self.assertTrue(settings2.equals(settings))
+
+        # equals
+        settings2.setLayer(rl2)
+        self.assertFalse(settings2.equals(settings))
+        settings2 = settings.clone()
+        settings2.setResolution(555)
+        self.assertFalse(settings2.equals(settings))
+        settings2 = settings.clone()
+        settings2.setSkirtHeight(1555)
+        self.assertFalse(settings2.equals(settings))
+        settings2 = settings.clone()
+        settings2.setVerticalScale(4)
+        self.assertFalse(settings2.equals(settings))
+        settings2 = settings.clone()
+        settings2.setMapTileResolution(136)
+        self.assertFalse(settings2.equals(settings))
+        settings2 = settings.clone()
+        settings2.setMaximumScreenError(136)
+        self.assertFalse(settings2.equals(settings))
+        settings2 = settings.clone()
+        settings2.setMaximumGroundError(136)
+        self.assertFalse(settings2.equals(settings))
+        settings2 = settings.clone()
+        settings2.setElevationOffset(136)
+        self.assertFalse(settings2.equals(settings))
+
+        # read/write xml
+        doc = QDomDocument("testdoc")
+        elem = doc.createElement("test")
+        settings.writeXml(elem, QgsReadWriteContext())
+
+        settings3 = QgsDemTerrainSettings()
+        settings3.readXml(elem, QgsReadWriteContext())
+        self.assertIsNone(settings3.layer())
+        settings3.resolveReferences(p)
+        self.assertEqual(settings3.layer(), rl)
+        self.assertEqual(settings3.resolution(), 66)
+        self.assertEqual(settings3.skirtHeight(), 366)
+        self.assertEqual(settings3.verticalScale(), 3)
+        self.assertEqual(settings3.mapTileResolution(), 36)
+        self.assertEqual(settings3.maximumScreenError(), 4.5)
+        self.assertEqual(settings3.maximumGroundError(), 14.5)
+        self.assertEqual(settings3.elevationOffset(), 24.5)
+
+    def test_mesh_terrain(self):
+        p = QgsProject()
+        ml = QgsMeshLayer(
+            self.get_test_data_path("mesh/quad_and_triangle.2dm").as_posix(), "layer1"
+        )
+        self.assertTrue(ml.isValid())
+        ml2 = QgsMeshLayer(
+            self.get_test_data_path("mesh/quad_and_triangle.2dm").as_posix(), "layer2"
+        )
+        self.assertTrue(ml2.isValid())
+        p.addMapLayer(ml)
+        p.addMapLayer(ml2)
+
+        settings = QgsMeshTerrainSettings.create()
+        self.assertIsInstance(settings, QgsMeshTerrainSettings)
+
+        settings.setLayer(ml)
+        self.assertEqual(settings.layer(), ml)
+
+        self.assertEqual(settings.verticalScale(), 1)
+        settings.setVerticalScale(3)
+        self.assertEqual(settings.verticalScale(), 3)
+
+        self.assertEqual(settings.mapTileResolution(), 512)
+        settings.setMapTileResolution(36)
+        self.assertEqual(settings.mapTileResolution(), 36)
+
+        self.assertEqual(settings.maximumScreenError(), 3.0)
+        settings.setMaximumScreenError(4.5)
+        self.assertEqual(settings.maximumScreenError(), 4.5)
+
+        self.assertEqual(settings.maximumGroundError(), 1)
+        settings.setMaximumGroundError(14.5)
+        self.assertEqual(settings.maximumGroundError(), 14.5)
+
+        self.assertEqual(settings.elevationOffset(), 0)
+        settings.setElevationOffset(24.5)
+        self.assertEqual(settings.elevationOffset(), 24.5)
+
+        # clone
+        settings2 = settings.clone()
+        self.assertEqual(settings2.layer(), ml)
+        self.assertEqual(settings2.verticalScale(), 3)
+        self.assertEqual(settings2.mapTileResolution(), 36)
+        self.assertEqual(settings2.maximumScreenError(), 4.5)
+        self.assertEqual(settings2.maximumGroundError(), 14.5)
+        self.assertEqual(settings2.elevationOffset(), 24.5)
+        self.assertTrue(settings2.equals(settings))
+
+        # equals
+        settings2.setLayer(ml2)
+        self.assertFalse(settings2.equals(settings))
+        settings2 = settings.clone()
+        settings2.setVerticalScale(4)
+        self.assertFalse(settings2.equals(settings))
+        settings2 = settings.clone()
+        settings2.setMapTileResolution(136)
+        self.assertFalse(settings2.equals(settings))
+        settings2 = settings.clone()
+        settings2.setMaximumScreenError(136)
+        self.assertFalse(settings2.equals(settings))
+        settings2 = settings.clone()
+        settings2.setMaximumGroundError(136)
+        self.assertFalse(settings2.equals(settings))
+        settings2 = settings.clone()
+        settings2.setElevationOffset(136)
+        self.assertFalse(settings2.equals(settings))
+
+        # read/write xml
+        doc = QDomDocument("testdoc")
+        elem = doc.createElement("test")
+        settings.writeXml(elem, QgsReadWriteContext())
+
+        settings3 = QgsMeshTerrainSettings()
+        settings3.readXml(elem, QgsReadWriteContext())
+        self.assertIsNone(settings3.layer())
+        settings3.resolveReferences(p)
+        self.assertEqual(settings3.layer(), ml)
+        self.assertEqual(settings3.verticalScale(), 3)
+        self.assertEqual(settings3.mapTileResolution(), 36)
+        self.assertEqual(settings3.maximumScreenError(), 4.5)
+        self.assertEqual(settings3.maximumGroundError(), 14.5)
+        self.assertEqual(settings3.elevationOffset(), 24.5)
+
+    def test_registry(self):
+        registry = Qgs3DTerrainRegistry()
+        # registry should be populated with known types
+        self.assertIn("flat", registry.types())
+        self.assertIn("dem", registry.types())
+        self.assertIn("mesh", registry.types())
+
+        # check settings
+        settings = registry.createTerrainSettings("flat")
+        self.assertIsInstance(settings, QgsFlatTerrainSettings)
+        settings = registry.createTerrainSettings("dem")
+        self.assertIsInstance(settings, QgsDemTerrainSettings)
+        settings = registry.createTerrainSettings("mesh")
+        self.assertIsInstance(settings, QgsMeshTerrainSettings)
+
+
+if __name__ == "__main__":
+    unittest.main()