Make style model decoration icons size responsive

We hack the model a bit here, but as much as possible avoid bleeding
view properties into the model API.

So we use a QObject property ("icon_size") to specify icons sizes
for the model to generate. This is set on instances
of the model to indicate the required sizes for decorations in all
views connected to the model, and allows the model to have size responsive icons.

By using a QObject property we avoid having public GUI/view related API within
the model, and mostly avoid view related properties contaminating the pure model,
yet still have pixel-perfect symbol renders for the required view icon sizes.

Author: nyalldawson

src/core/symbology/qgsstylemodel.cpp

@@ -18,6 +18,7 @@
 #include "qgssymbollayerutils.h"
 #include <QIcon>
 
+const double ICON_PADDING_FACTOR = 0.16;
 
 QgsStyleModel::QgsStyleModel( QgsStyle *style, QObject *parent )
   : QAbstractItemModel( parent )
@@ -70,18 +71,41 @@ QVariant QgsStyleModel::data( const QModelIndex &index, int role ) const
 
     case Qt::DecorationRole:
     {
+      // check the model custom property for icon sizes to generate. This is used
+      // by instances of the model to indicate the required sizes for decorations in all
+      // views connected to the model, and allows the model to have size responsive icons.
+      // By using a QObject property we avoid having public GUI/view related API within
+      // the model, and mostly avoid view related properties contaminating the pure model...
+      const QVariantList iconSizes = property( "icon_sizes" ).toList();
+
       switch ( index.column() )
       {
         case Name:
           if ( !isColorRamp )
           {
             std::unique_ptr< QgsSymbol > symbol( mStyle->symbol( name ) );
-            return QgsSymbolLayerUtils::symbolPreviewIcon( symbol.get(), QSize( 24, 24 ), 2 );
+            QIcon icon;
+            icon.addPixmap( QgsSymbolLayerUtils::symbolPreviewPixmap( symbol.get(), QSize( 24, 24 ), 1 ) );
+
+            for ( const QVariant &size : iconSizes )
+            {
+              QSize s = size.toSize();
+              icon.addPixmap( QgsSymbolLayerUtils::symbolPreviewPixmap( symbol.get(), s, static_cast< int >( s.width() * ICON_PADDING_FACTOR ) ) );
+            }
+
+            return icon;
           }
           else
           {
             std::unique_ptr< QgsColorRamp > ramp( mStyle->colorRamp( name ) );
-            return QgsSymbolLayerUtils::colorRampPreviewIcon( ramp.get(), QSize( 24, 24 ), 2 );
+            QIcon icon;
+            icon.addPixmap( QgsSymbolLayerUtils::colorRampPreviewPixmap( ramp.get(), QSize( 24, 24 ), 1 ) );
+            for ( const QVariant &size : iconSizes )
+            {
+              QSize s = size.toSize();
+              icon.addPixmap( QgsSymbolLayerUtils::colorRampPreviewPixmap( ramp.get(), s, static_cast< int >( s.width() * ICON_PADDING_FACTOR ) ) );
+            }
+            return icon;
           }
         case Tags:
           return QVariant();

tests/src/python/test_qgsstylemodel.py

@@ -23,7 +23,7 @@
                        QgsStyle,
                        QgsStyleProxyModel)
 from qgis.testing import start_app, unittest
-from qgis.PyQt.QtCore import Qt
+from qgis.PyQt.QtCore import Qt, QSize
 from qgis.PyQt.QtGui import QColor
 
 start_app()
@@ -715,6 +715,49 @@ def test_filter_proxy(self):
         model.setSmartGroupId(-1)
         self.assertEqual(model.rowCount(), 8)
 
+    def testIconSize(self):
+        """
+        Test that model has responsive icon sizes for decorations
+        """
+        style = QgsStyle()
+        style.createMemoryDatabase()
+
+        symbol_a = createMarkerSymbol()
+        symbol_a.setColor(QColor(255, 10, 10))
+        self.assertTrue(style.addSymbol('a', symbol_a, True))
+        ramp_a = QgsLimitedRandomColorRamp(5)
+        self.assertTrue(style.addColorRamp('ramp a', ramp_a, True))
+
+        model = QgsStyleModel(style)
+        self.assertEqual(model.rowCount(), 2)
+        for i in range(2):
+            icon = model.data(model.index(i, 0), Qt.DecorationRole)
+            # by default, only 24x24 icon
+            self.assertEqual(icon.availableSizes(), [QSize(24, 24)])
+            self.assertEqual(icon.actualSize(QSize(10, 10)), QSize(10, 10))
+            self.assertEqual(icon.actualSize(QSize(24, 24)), QSize(24, 24))
+            self.assertEqual(icon.actualSize(QSize(90, 90)), QSize(24, 24))
+
+            model.setProperty('icon_sizes', [QSize(24, 24), QSize(100, 90)])
+            icon = model.data(model.index(i, 0), Qt.DecorationRole)
+            self.assertEqual(icon.availableSizes(), [QSize(24, 24), QSize(100, 90)])
+            self.assertEqual(icon.actualSize(QSize(10, 10)), QSize(10, 10))
+            self.assertEqual(icon.actualSize(QSize(24, 24)), QSize(24, 24))
+            self.assertEqual(icon.actualSize(QSize(25, 25)), QSize(25, 22))
+            self.assertEqual(icon.actualSize(QSize(90, 90)), QSize(90, 81))
+            self.assertEqual(icon.actualSize(QSize(125, 125)), QSize(100, 90))
+
+            model.setProperty('icon_sizes', [QSize(100, 90), QSize(200, 180)])
+            icon = model.data(model.index(i, 0), Qt.DecorationRole)
+            self.assertEqual(icon.availableSizes(), [QSize(24, 24), QSize(100, 90), QSize(200, 180)])
+            self.assertEqual(icon.actualSize(QSize(10, 10)), QSize(10, 10))
+            self.assertEqual(icon.actualSize(QSize(24, 24)), QSize(24, 24))
+            self.assertEqual(icon.actualSize(QSize(25, 25)), QSize(25, 22))
+            self.assertEqual(icon.actualSize(QSize(90, 90)), QSize(90, 81))
+            self.assertEqual(icon.actualSize(QSize(125, 125)), QSize(125, 112))
+            self.assertEqual(icon.actualSize(QSize(225, 225)), QSize(200, 180))
+            model.setProperty('icon_sizes', None)
+
 
 if __name__ == '__main__':
     unittest.main()