New class QgsMapClippingUtils with utility functions for helping

with map clipping

python/core/auto_generated/qgsmapclippingutils.sip.in

@@ -0,0 +1,53 @@
+/************************************************************************
+ * This file has been generated automatically from                      *
+ *                                                                      *
+ * src/core/qgsmapclippingutils.h                                       *
+ *                                                                      *
+ * Do not edit manually ! Edit header and run scripts/sipify.pl again   *
+ ************************************************************************/
+
+
+
+
+class QgsMapClippingUtils
+{
+%Docstring
+
+Utility functions for use when clipping map renders.
+
+.. versionadded:: 3.16
+%End
+
+%TypeHeaderCode
+#include "qgsmapclippingutils.h"
+%End
+  public:
+
+    static QList< QgsMapClippingRegion > collectClippingRegionsForLayer( const QgsRenderContext &context, const QgsMapLayer *layer );
+%Docstring
+Collects the list of map clipping regions from a ``context`` which apply to a map ``layer``.
+%End
+
+    static QgsGeometry calculateFeatureRequestGeometry( const QList< QgsMapClippingRegion > &regions, const QgsRenderContext &context, bool &shouldFilter );
+%Docstring
+Returns the geometry representing the intersection of clipping ``regions`` from ``context``.
+
+The returned geometry will be automatically reprojected into the same CRS as the source layer, ready for use for filtering
+a feature request.
+
+:param regions: list of clip regions which apply to the layer
+:param context: a render context
+:param shouldFilter: will be set to ``True`` if layer's features should be filtered, i.e. one or more clipping regions applies to the layer
+
+:return: combined clipping region for use when filtering features to render
+%End
+
+};
+
+/************************************************************************
+ * This file has been generated automatically from                      *
+ *                                                                      *
+ * src/core/qgsmapclippingutils.h                                       *
+ *                                                                      *
+ * Do not edit manually ! Edit header and run scripts/sipify.pl again   *
+ ************************************************************************/

python/core/core_auto.sip

@@ -102,6 +102,7 @@
 %Include auto_generated/qgslocalizeddatapathregistry.sip
 %Include auto_generated/qgslogger.sip
 %Include auto_generated/qgsmapclippingregion.sip
+%Include auto_generated/qgsmapclippingutils.sip
 %Include auto_generated/qgsmapdecoration.sip
 %Include auto_generated/qgsmaphittest.sip
 %Include auto_generated/qgsmaplayer.sip

src/core/CMakeLists.txt

@@ -312,6 +312,7 @@ SET(QGIS_CORE_SRCS
   qgslocalizeddatapathregistry.cpp
   qgslogger.cpp
   qgsmapclippingregion.cpp
+  qgsmapclippingutils.cpp
   qgsmapdecoration.cpp
   qgsmaphittest.cpp
   qgsmaplayer.cpp
@@ -861,6 +862,7 @@ SET(QGIS_CORE_HDRS
   qgslocalizeddatapathregistry.h
   qgslogger.h
   qgsmapclippingregion.h
+  qgsmapclippingutils.h
   qgsmapdecoration.h
   qgsmaphittest.h
   qgsmaplayer.h

src/core/qgsmapclippingutils.cpp

@@ -0,0 +1,75 @@
+/***************************************************************************
+  qgsmapclippingutils.cpp
+  --------------------------------------
+  Date                 : June 2020
+  Copyright            : (C) 2020 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 "qgsmapclippingutils.h"
+#include "qgsgeometry.h"
+#include "qgsrendercontext.h"
+#include "qgsmapclippingregion.h"
+#include "qgslogger.h"
+#include <algorithm>
+
+QList<QgsMapClippingRegion> QgsMapClippingUtils::collectClippingRegionsForLayer( const QgsRenderContext &context, const QgsMapLayer *layer )
+{
+  QList< QgsMapClippingRegion > res;
+  const QList< QgsMapClippingRegion > regions = context.clippingRegions();
+  res.reserve( regions.size() );
+
+  std::copy_if( regions.begin(), regions.end(), std::back_inserter( res ), [layer]( const QgsMapClippingRegion & region )
+  {
+    return region.appliesToLayer( layer );
+  } );
+
+  return res;
+}
+
+QgsGeometry QgsMapClippingUtils::calculateFeatureRequestGeometry( const QList< QgsMapClippingRegion > &regions, const QgsRenderContext &context, bool &shouldFilter )
+{
+  QgsGeometry result;
+  bool first = true;
+  shouldFilter = false;
+  for ( const QgsMapClippingRegion &region : regions )
+  {
+    if ( region.geometry().type() != QgsWkbTypes::PolygonGeometry )
+      continue;
+
+    shouldFilter = true;
+    if ( first )
+    {
+      result = region.geometry();
+      first = false;
+    }
+    else
+    {
+      result = result.intersection( region.geometry() );
+    }
+  }
+
+  // filter out polygon parts from result only
+  result.convertGeometryCollectionToSubclass( QgsWkbTypes::PolygonGeometry );
+
+  // lastly transform back to layer CRS
+  try
+  {
+    result.transform( context.coordinateTransform(), QgsCoordinateTransform::ReverseTransform );
+  }
+  catch ( QgsCsException & )
+  {
+    QgsDebugMsg( QStringLiteral( "Could not transform clipping region to layer CRS" ) );
+    shouldFilter = false;
+    return QgsGeometry();
+  }
+
+  return result;
+}

src/core/qgsmapclippingutils.h

@@ -0,0 +1,61 @@
+/***************************************************************************
+  qgsmapclippingutils.h
+  --------------------------------------
+  Date                 : June 2020
+  Copyright            : (C) 2020 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 QGSMAPCLIPPINGUTILS_H
+#define QGSMAPCLIPPINGUTILS_H
+
+#include "qgis_core.h"
+#include "qgis_sip.h"
+#include <QList>
+
+class QgsRenderContext;
+class QgsMapLayer;
+class QgsGeometry;
+class QgsMapClippingRegion;
+
+/**
+ * \class QgsMapClippingUtils
+ * \ingroup core
+ *
+ * Utility functions for use when clipping map renders.
+ *
+ * \since QGIS 3.16
+*/
+class CORE_EXPORT QgsMapClippingUtils
+{
+  public:
+
+    /**
+     * Collects the list of map clipping regions from a \a context which apply to a map \a layer.
+     */
+    static QList< QgsMapClippingRegion > collectClippingRegionsForLayer( const QgsRenderContext &context, const QgsMapLayer *layer );
+
+    /**
+     * Returns the geometry representing the intersection of clipping \a regions from \a context.
+     *
+     * The returned geometry will be automatically reprojected into the same CRS as the source layer, ready for use for filtering
+     * a feature request.
+     *
+     * \param regions list of clip regions which apply to the layer
+     * \param context a render context
+     * \param shouldFilter will be set to TRUE if layer's features should be filtered, i.e. one or more clipping regions applies to the layer
+     *
+     * \returns combined clipping region for use when filtering features to render
+     */
+    static QgsGeometry calculateFeatureRequestGeometry( const QList< QgsMapClippingRegion > &regions, const QgsRenderContext &context, bool &shouldFilter );
+
+};
+
+#endif // QGSMAPCLIPPINGUTILS_H

tests/src/python/CMakeLists.txt

@@ -149,6 +149,7 @@ ADD_PYTHON_TEST(PyQgsLocator test_qgslocator.py)
 ADD_PYTHON_TEST(PyQgsMapCanvas test_qgsmapcanvas.py)
 ADD_PYTHON_TEST(PyQgsMapCanvasAnnotationItem test_qgsmapcanvasannotationitem.py)
 ADD_PYTHON_TEST(PyQgsMapClippingRegion test_qgsmapclippingregion.py)
+ADD_PYTHON_TEST(PyQgsMapClippingUtils test_qgsmapclippingutils.py)
 ADD_PYTHON_TEST(PyQgsMapLayer test_qgsmaplayer.py)
 ADD_PYTHON_TEST(PyQgsMapLayerAction test_qgsmaplayeraction.py)
 ADD_PYTHON_TEST(PyQgsMapLayerComboBox test_qgsmaplayercombobox.py)

tests/src/python/test_qgsmapclippingutils.py

@@ -0,0 +1,84 @@
+# -*- coding: utf-8 -*-
+"""QGIS Unit tests for QgsMapClippingUtils.
+
+.. 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.
+"""
+__author__ = 'Nyall Dawson'
+__date__ = '2020-06'
+__copyright__ = 'Copyright 2020, The QGIS Project'
+
+import qgis  # NOQA
+
+from qgis.testing import unittest
+from qgis.core import (
+    QgsMapClippingRegion,
+    QgsMapClippingUtils,
+    QgsMapSettings,
+    QgsRenderContext,
+    QgsGeometry,
+    QgsVectorLayer,
+    QgsCoordinateTransform,
+    QgsCoordinateReferenceSystem,
+    QgsProject
+)
+
+
+class TestQgsMapClippingUtils(unittest.TestCase):
+
+    def testClippingRegionsForLayer(self):
+        layer = QgsVectorLayer("Point?field=fldtxt:string&field=fldint:integer",
+                               "addfeat", "memory")
+        layer2 = QgsVectorLayer("Point?field=fldtxt:string&field=fldint:integer",
+                                "addfeat", "memory")
+
+        region = QgsMapClippingRegion(QgsGeometry.fromWkt('Polygon((0 0, 1 0, 1 1, 0 1, 0 0))'))
+        region2 = QgsMapClippingRegion(QgsGeometry.fromWkt('Polygon((0 0, 0.1 0, 0.1 2, 0 2, 0 0))'))
+        region2.setRestrictedLayers([layer])
+        ms = QgsMapSettings()
+        ms.addClippingRegion(region)
+        ms.addClippingRegion(region2)
+        rc = QgsRenderContext.fromMapSettings(ms)
+
+        regions = QgsMapClippingUtils.collectClippingRegionsForLayer(rc, layer)
+        self.assertEqual(len(regions), 2)
+        self.assertEqual(regions[0].geometry().asWkt(1), 'Polygon ((0 0, 1 0, 1 1, 0 1, 0 0))')
+        self.assertEqual(regions[1].geometry().asWkt(1), 'Polygon ((0 0, 0.1 0, 0.1 2, 0 2, 0 0))')
+
+        regions = QgsMapClippingUtils.collectClippingRegionsForLayer(rc, layer2)
+        self.assertEqual(len(regions), 1)
+        self.assertEqual(regions[0].geometry().asWkt(1), 'Polygon ((0 0, 1 0, 1 1, 0 1, 0 0))')
+
+    def testCalculateFeatureRequestGeometry(self):
+        layer = QgsVectorLayer("Point?field=fldtxt:string&field=fldint:integer",
+                               "addfeat", "memory")
+        layer2 = QgsVectorLayer("Point?field=fldtxt:string&field=fldint:integer",
+                                "addfeat", "memory")
+
+        region = QgsMapClippingRegion(QgsGeometry.fromWkt('Polygon((0 0, 1 0, 1 1, 0 1, 0 0))'))
+        region2 = QgsMapClippingRegion(QgsGeometry.fromWkt('Polygon((0 0, 0.1 0, 0.1 2, 0 2, 0 0))'))
+
+        rc = QgsRenderContext()
+
+        geom, should_clip = QgsMapClippingUtils.calculateFeatureRequestGeometry([], rc)
+        self.assertFalse(should_clip)
+        self.assertTrue(geom.isNull())
+
+        geom, should_clip = QgsMapClippingUtils.calculateFeatureRequestGeometry([region], rc)
+        self.assertTrue(should_clip)
+        self.assertEqual(geom.asWkt(1), 'Polygon ((0 0, 1 0, 1 1, 0 1, 0 0))')
+
+        geom, should_clip = QgsMapClippingUtils.calculateFeatureRequestGeometry([region, region2], rc)
+        self.assertTrue(should_clip)
+        self.assertEqual(geom.asWkt(1), 'Polygon ((0.1 0, 0 0, 0 1, 0.1 1, 0.1 0))')
+
+        rc.setCoordinateTransform(QgsCoordinateTransform(QgsCoordinateReferenceSystem('EPSG:3857'), QgsCoordinateReferenceSystem('EPSG:4326'), QgsProject.instance()))
+        geom, should_clip = QgsMapClippingUtils.calculateFeatureRequestGeometry([region, region2], rc)
+        self.assertTrue(should_clip)
+        self.assertEqual(geom.asWkt(0), 'Polygon ((11132 0, 0 0, 0 111325, 11132 111325, 11132 0))')
+
+
+if __name__ == '__main__':
+    unittest.main()