Add pixel size limiting for labels defined in map units

- Allows user to quickly set visibility thresholds based upon text legibility
- By default initially on for map unit labels to skip rendering at sizes < 3 px

python/core/qgspallabeling.sip

@@ -121,6 +121,9 @@ class QgsPalLayerSettings
     bool addDirectionSymbol;
     unsigned int upsidedownLabels; // whether, or how, to show upsidedown labels
     bool fontSizeInMapUnits; //true if font size is in map units (otherwise in points)
+    bool fontLimitPixelSize; // true is label should be limited by fontMinPixelSize/fontMaxPixelSize
+    int fontMinPixelSize; // minimum pixel size for showing rendered map unit labels (1 - 1000)
+    int fontMaxPixelSize; // maximum pixel size for showing rendered map unit labels (1 - 10000)
     bool bufferSizeInMapUnits; //true if buffer is in map units (otherwise in mm)
     bool labelOffsetInMapUnits; //true if label offset is in map units (otherwise in mm)
     bool distInMapUnits; //true if distance is in map units (otherwise in mm)

src/app/qgslabelinggui.cpp

@@ -239,6 +239,12 @@ QgsLabelingGui::QgsLabelingGui( QgsPalLabeling* lbl, QgsVectorLayer* layer, QgsM
     chkPlusSign->setChecked( plusSign );
   }
 
+  // set pixel size limiting checked state before unit choice so limiting can be
+  // turned on as a default for map units, if minimum trigger value of 0 is used
+  mFontLimitPixelGroupBox->setChecked( lyr.fontLimitPixelSize );
+  mMinPixelLimit = lyr.fontMinPixelSize; // ignored after first settings save
+  mFontMinPixelSpinBox->setValue( lyr.fontMinPixelSize == 0 ? 3 : lyr.fontMinPixelSize );
+  mFontMaxPixelSpinBox->setValue( lyr.fontMaxPixelSize );
   if ( lyr.fontSizeInMapUnits )
   {
     mFontSizeUnitComboBox->setCurrentIndex( 1 );
@@ -465,6 +471,9 @@ QgsPalLayerSettings QgsLabelingGui::layerSettings()
   }
   lyr.minFeatureSize = mMinSizeSpinBox->value();
   lyr.fontSizeInMapUnits = ( mFontSizeUnitComboBox->currentIndex() == 1 );
+  lyr.fontLimitPixelSize = mFontLimitPixelGroupBox->isChecked();
+  lyr.fontMinPixelSize = mFontMinPixelSpinBox->value();
+  lyr.fontMaxPixelSize = mFontMaxPixelSpinBox->value();
   lyr.wrapChar = wrapCharacterEdit->text();
   lyr.multilineHeight = mFontLineHeightSpinBox->value();
   lyr.multilineAlign = ( QgsPalLayerSettings::MultiLineAlign ) mFontMultiLineComboBox->currentIndex();
@@ -1004,10 +1013,39 @@ void QgsLabelingGui::on_mFontLetterSpacingSpinBox_valueChanged( double spacing )
 
 void QgsLabelingGui::on_mFontSizeUnitComboBox_currentIndexChanged( int index )
 {
-  Q_UNUSED( index );
+  // disable pixel size limiting for labels defined in points
+  if ( index == 0 )
+  {
+    mFontLimitPixelGroupBox->setChecked( false );
+  }
+  else if ( index == 1 && mMinPixelLimit == 0 )
+  {
+    // initial minimum trigger value set, turn on pixel size limiting by default
+    // for labels defined in map units (ignored after first settings save)
+    mFontLimitPixelGroupBox->setChecked( true );
+  }
   updateFont( mRefFont );
 }
 
+void QgsLabelingGui::on_mFontMinPixelSpinBox_valueChanged( int px )
+{
+  // ensure max font pixel size for map unit labels can't be lower than min
+  mFontMaxPixelSpinBox->setMinimum( px );
+  mFontMaxPixelSpinBox->update();
+}
+
+void QgsLabelingGui::on_mFontMaxPixelSpinBox_valueChanged( int px )
+{
+  // ensure max font pixel size for map unit labels can't be lower than min
+  if ( px < mFontMinPixelSpinBox->value() )
+  {
+    mFontMaxPixelSpinBox->blockSignals( true );
+    mFontMaxPixelSpinBox->setValue( mFontMinPixelSpinBox->value() );
+    mFontMaxPixelSpinBox->blockSignals( false );
+  }
+  mFontMaxPixelSpinBox->setMinimum( mFontMinPixelSpinBox->value() );
+}
+
 void QgsLabelingGui::on_mBufferUnitComboBox_currentIndexChanged( int index )
 {
   Q_UNUSED( index );

src/app/qgslabelinggui.h

@@ -61,6 +61,8 @@ class QgsLabelingGui : public QWidget, private Ui::QgsLabelingGuiBase
     void on_mFontWordSpacingSpinBox_valueChanged( double spacing );
     void on_mFontLetterSpacingSpinBox_valueChanged( double spacing );
     void on_mFontSizeUnitComboBox_currentIndexChanged( int index );
+    void on_mFontMinPixelSpinBox_valueChanged( int px );
+    void on_mFontMaxPixelSpinBox_valueChanged( int px );
     void on_mBufferUnitComboBox_currentIndexChanged( int index );
     void on_mXCoordinateComboBox_currentIndexChanged( const QString & text );
     void on_mYCoordinateComboBox_currentIndexChanged( const QString & text );
@@ -95,6 +97,7 @@ class QgsLabelingGui : public QWidget, private Ui::QgsLabelingGuiBase
 
     int mXQuadOffset;
     int mYQuadOffset;
+    int mMinPixelLimit;
 
     void disableDataDefinedAlignment();
     void enableDataDefinedAlignment();

src/core/qgspallabeling.cpp

@@ -215,6 +215,9 @@ QgsPalLayerSettings::QgsPalLayerSettings()
   addDirectionSymbol = false;
   upsidedownLabels = Upright;
   fontSizeInMapUnits = false;
+  fontLimitPixelSize = false;
+  fontMinPixelSize = 0; //trigger to turn it on by default for map unit labels
+  fontMaxPixelSize = 10000;
   bufferSizeInMapUnits = false;
   labelOffsetInMapUnits = true;
   distInMapUnits = false;
@@ -265,6 +268,9 @@ QgsPalLayerSettings::QgsPalLayerSettings( const QgsPalLayerSettings& s )
   addDirectionSymbol = s.addDirectionSymbol;
   upsidedownLabels = s.upsidedownLabels;
   fontSizeInMapUnits = s.fontSizeInMapUnits;
+  fontLimitPixelSize = s.fontLimitPixelSize;
+  fontMinPixelSize = s.fontMinPixelSize;
+  fontMaxPixelSize = s.fontMaxPixelSize;
   bufferSizeInMapUnits = s.bufferSizeInMapUnits;
   distInMapUnits = s.distInMapUnits;
   labelOffsetInMapUnits = s.labelOffsetInMapUnits;
@@ -448,6 +454,9 @@ void QgsPalLayerSettings::readFromLayer( QgsVectorLayer* layer )
   upsidedownLabels = ( UpsideDownLabels ) layer->customProperty( "labeling/upsidedownLabels", QVariant( Upright ) ).toUInt();
   minFeatureSize = layer->customProperty( "labeling/minFeatureSize" ).toDouble();
   fontSizeInMapUnits = layer->customProperty( "labeling/fontSizeInMapUnits" ).toBool();
+  fontLimitPixelSize = layer->customProperty( "labeling/fontLimitPixelSize", QVariant( false ) ).toBool();
+  fontMinPixelSize = layer->customProperty( "labeling/fontMinPixelSize", QVariant( 0 ) ).toInt();
+  fontMaxPixelSize = layer->customProperty( "labeling/fontMaxPixelSize", QVariant( 10000 ) ).toInt();
   bufferSizeInMapUnits = layer->customProperty( "labeling/bufferSizeInMapUnits" ).toBool();
   distInMapUnits = layer->customProperty( "labeling/distInMapUnits" ).toBool();
   labelOffsetInMapUnits = layer->customProperty( "labeling/labelOffsetInMapUnits", QVariant( true ) ).toBool();
@@ -509,6 +518,9 @@ void QgsPalLayerSettings::writeToLayer( QgsVectorLayer* layer )
   layer->setCustomProperty( "labeling/upsidedownLabels", ( unsigned int )upsidedownLabels );
   layer->setCustomProperty( "labeling/minFeatureSize", minFeatureSize );
   layer->setCustomProperty( "labeling/fontSizeInMapUnits", fontSizeInMapUnits );
+  layer->setCustomProperty( "labeling/fontLimitPixelSize", fontLimitPixelSize );
+  layer->setCustomProperty( "labeling/fontMinPixelSize", fontMinPixelSize );
+  layer->setCustomProperty( "labeling/fontMaxPixelSize", fontMaxPixelSize );
   layer->setCustomProperty( "labeling/bufferSizeInMapUnits", bufferSizeInMapUnits );
   layer->setCustomProperty( "labeling/distInMapUnits", distInMapUnits );
   layer->setCustomProperty( "labeling/labelOffsetInMapUnits", labelOffsetInMapUnits );
@@ -658,6 +670,33 @@ void QgsPalLayerSettings::registerFeature( QgsVectorLayer* layer,  QgsFeature& f
     }
   }
 
+  QFont labelFont = textFont;
+
+  //data defined label size?
+  QMap< DataDefinedProperties, int >::const_iterator it = dataDefinedProperties.find( QgsPalLayerSettings::Size );
+  if ( it != dataDefinedProperties.constEnd() )
+  {
+    //find out size
+    QVariant size = f.attributeMap().value( *it );
+    if ( size.isValid() )
+    {
+      double sizeDouble = size.toDouble();
+      if ( sizeDouble <= 0.0 || sizeToPixel( sizeDouble, context ) < 1 )
+      {
+        return;
+      }
+      labelFont.setPixelSize( sizeToPixel( sizeDouble, context ) );
+    }
+  }
+
+  // defined 'minimum/maximum pixel font size' option
+  // TODO: add any data defined setting to override fontMinPixelSize/fontMaxPixelSize
+  if ( fontLimitPixelSize && fontSizeInMapUnits &&
+       ( fontMinPixelSize > labelFont.pixelSize()  || labelFont.pixelSize() > fontMaxPixelSize ) )
+  {
+    return;
+  }
+
   QString labelText;
 
   // Check to see if we are a expression string.
@@ -695,28 +734,9 @@ void QgsPalLayerSettings::registerFeature( QgsVectorLayer* layer,  QgsFeature& f
     labelText = f.attributeMap()[fieldIndex].toString();
   }
 
-  double labelX, labelY; // will receive label size
-  QFont labelFont = textFont;
-
-  //data defined label size?
-  QMap< DataDefinedProperties, int >::const_iterator it = dataDefinedProperties.find( QgsPalLayerSettings::Size );
-  if ( it != dataDefinedProperties.constEnd() )
-  {
-    //find out size
-    QVariant size = f.attributeMap().value( *it );
-    if ( size.isValid() )
-    {
-      double sizeDouble = size.toDouble();
-      if ( sizeDouble <= 0.0 || sizeToPixel( sizeDouble, context ) < 1 )
-      {
-        return;
-      }
-      labelFont.setPixelSize( sizeToPixel( sizeDouble, context ) );
-    }
-  }
-
-  // this should come after any data defined option that affects font metrics
+  // this should come AFTER any data defined option that affects font metrics
   QFontMetricsF* labelFontMetrics = new QFontMetricsF( labelFont );
+  double labelX, labelY; // will receive label size
   calculateLabelSize( labelFontMetrics, labelText, labelX, labelY );
 
   QgsGeometry* geom = f.geometry();

src/core/qgspallabeling.h

@@ -175,6 +175,9 @@ class CORE_EXPORT QgsPalLayerSettings
     bool addDirectionSymbol;
     unsigned int upsidedownLabels; // whether, or how, to show upsidedown labels
     bool fontSizeInMapUnits; //true if font size is in map units (otherwise in points)
+    bool fontLimitPixelSize; // true is label should be limited by fontMinPixelSize/fontMaxPixelSize
+    int fontMinPixelSize; // minimum pixel size for showing rendered map unit labels (1 - 1000)
+    int fontMaxPixelSize; // maximum pixel size for showing rendered map unit labels (1 - 10000)
     bool bufferSizeInMapUnits; //true if buffer is in map units (otherwise in mm)
     bool labelOffsetInMapUnits; //true if label offset is in map units (otherwise in mm)
     bool distInMapUnits; //true if distance is in map units (otherwise in mm)