Fix missing min/max values for classification when changing datasets

The min/max values were stored in the color ramp shader, but to my surprise
these values were never persisted or copied: pseudo-color raster renderer
has a separate storage for the min/max values, so we need that for mesh renderer
as well.

The QgsRasterShaderFunction is not really useful, and QgsColorRamp should not
be derived from it, making things just more confusing.

python/core/auto_generated/mesh/qgsmeshrenderersettings.sip.in

@@ -90,6 +90,19 @@ Returns color ramp shader function
     void setColorRampShader( const QgsColorRampShader &shader );
 %Docstring
 Sets color ramp shader function
+%End
+
+    double classificationMin() const;
+%Docstring
+Returns min value used for creation of the color ramp shader
+%End
+    double classificationMax() const;
+%Docstring
+Returns max value used for creation of the color ramp shader
+%End
+    void setClassificationMinMax( double vMin, double vMax );
+%Docstring
+Sets min/max values used for creation of the color ramp shader
 %End
 
     QDomElement writeXml( QDomDocument &doc ) const;

src/app/mesh/qgsmeshrendererscalarsettingswidget.cpp

@@ -45,6 +45,7 @@ QgsMeshRendererScalarSettings QgsMeshRendererScalarSettingsWidget::settings() co
 {
   QgsMeshRendererScalarSettings settings;
   settings.setColorRampShader( mScalarColorRampShaderWidget->shader() );
+  settings.setClassificationMinMax( lineEditValue( mScalarMinLineEdit ), lineEditValue( mScalarMaxLineEdit ) );
   return settings;
 }
 
@@ -59,8 +60,8 @@ void QgsMeshRendererScalarSettingsWidget::syncToLayer( )
   const QgsMeshRendererSettings rendererSettings = mMeshLayer->rendererSettings();
   const QgsMeshRendererScalarSettings settings = rendererSettings.scalarSettings( mActiveDatasetGroup );
   const QgsColorRampShader shader = settings.colorRampShader();
-  whileBlocking( mScalarMinLineEdit )->setText( QString::number( shader.minimumValue() ) );
-  whileBlocking( mScalarMaxLineEdit )->setText( QString::number( shader.maximumValue() ) );
+  whileBlocking( mScalarMinLineEdit )->setText( QString::number( settings.classificationMin() ) );
+  whileBlocking( mScalarMaxLineEdit )->setText( QString::number( settings.classificationMax() ) );
   whileBlocking( mScalarColorRampShaderWidget )->setFromShader( shader );
 }
 

src/core/mesh/qgsmeshlayer.cpp

@@ -216,6 +216,7 @@ void QgsMeshLayer::assignDefaultStyleToDatasetGroup( int groupIndex )
   fcn.classifyColorRamp( 5, -1, QgsRectangle(), nullptr );
 
   QgsMeshRendererScalarSettings scalarSettings;
+  scalarSettings.setClassificationMinMax( groupMin, groupMax );
   scalarSettings.setColorRampShader( fcn );
   mRendererSettings.setScalarSettings( groupIndex, scalarSettings );
 }

src/core/mesh/qgsmeshlayerrenderer.cpp

@@ -205,13 +205,14 @@ void QgsMeshLayerRenderer::renderScalarDataset()
   if ( !index.isValid() )
     return; // no shader
 
-  QgsColorRampShader *fcn = new QgsColorRampShader( mRendererSettings.scalarSettings( index.group() ).colorRampShader() );
+  const QgsMeshRendererScalarSettings scalarSettings = mRendererSettings.scalarSettings( index.group() );
+  QgsColorRampShader *fcn = new QgsColorRampShader( scalarSettings.colorRampShader() );
   QgsRasterShader *sh = new QgsRasterShader();
   sh->setRasterShaderFunction( fcn );  // takes ownership of fcn
   QgsMeshLayerInterpolator interpolator( mTriangularMesh, mScalarDatasetValues, mScalarDataOnVertices, mContext, mOutputSize );
   QgsSingleBandPseudoColorRenderer renderer( &interpolator, 0, sh );  // takes ownership of sh
-  renderer.setClassificationMin( fcn->minimumValue() );
-  renderer.setClassificationMax( fcn->maximumValue() );
+  renderer.setClassificationMin( scalarSettings.classificationMin() );
+  renderer.setClassificationMax( scalarSettings.classificationMax() );
 
   std::unique_ptr<QgsRasterBlock> bl( renderer.block( 0, mContext.extent(), mOutputSize.width(), mOutputSize.height(), mFeedback.get() ) );
   QImage img = bl->image();

src/core/mesh/qgsmeshrenderersettings.cpp

@@ -78,9 +78,17 @@ void QgsMeshRendererScalarSettings::setColorRampShader( const QgsColorRampShader
   mColorRampShader = shader;
 }
 
+void QgsMeshRendererScalarSettings::setClassificationMinMax( double vMin, double vMax )
+{
+  mClassificationMin = vMin;
+  mClassificationMax = vMax;
+}
+
 QDomElement QgsMeshRendererScalarSettings::writeXml( QDomDocument &doc ) const
 {
   QDomElement elem = doc.createElement( "scalar-settings" );
+  elem.setAttribute( "min-val", mClassificationMin );
+  elem.setAttribute( "max-val", mClassificationMax );
   QDomElement elemShader = mColorRampShader.writeXml( doc );
   elem.appendChild( elemShader );
   return elem;
@@ -88,6 +96,8 @@ QDomElement QgsMeshRendererScalarSettings::writeXml( QDomDocument &doc ) const
 
 void QgsMeshRendererScalarSettings::readXml( const QDomElement &elem )
 {
+  mClassificationMin = elem.attribute( "min-val" ).toDouble();
+  mClassificationMax = elem.attribute( "max-val" ).toDouble();
   QDomElement elemShader = elem.firstChildElement( QStringLiteral( "colorrampshader" ) );
   mColorRampShader.readXml( elemShader );
 }

src/core/mesh/qgsmeshrenderersettings.h

@@ -82,6 +82,13 @@ class CORE_EXPORT QgsMeshRendererScalarSettings
     //! Sets color ramp shader function
     void setColorRampShader( const QgsColorRampShader &shader );
 
+    //! Returns min value used for creation of the color ramp shader
+    double classificationMin() const { return mClassificationMin; }
+    //! Returns max value used for creation of the color ramp shader
+    double classificationMax() const { return mClassificationMax; }
+    //! Sets min/max values used for creation of the color ramp shader
+    void setClassificationMinMax( double vMin, double vMax );
+
     //! Writes configuration to a new DOM element
     QDomElement writeXml( QDomDocument &doc ) const;
     //! Reads configuration from the given DOM element
@@ -89,6 +96,8 @@ class CORE_EXPORT QgsMeshRendererScalarSettings
 
   private:
     QgsColorRampShader mColorRampShader;
+    double mClassificationMin = 0;
+    double mClassificationMax = 0;
 };
 
 /**

src/ui/mesh/qgsmeshrendererscalarsettingswidgetbase.ui

@@ -47,7 +47,7 @@
      <item>
       <widget class="QPushButton" name="mScalarRecalculateMinMaxButton">
        <property name="text">
-        <string>Recalculate</string>
+        <string>Load</string>
        </property>
       </widget>
      </item>