[plots] Add QgsBarChart and QgsLineChart classes, implement category typed axis rendering

python/PyQt6/core/auto_additions/qgsplot.py

@@ -13,25 +13,27 @@ try:
     QgsPlot.__group__ = ['plot']
 except (NameError, AttributeError):
     pass
+try:
+    QgsAbstractPlotSeries.__virtual_methods__ = ['categories']
+    QgsAbstractPlotSeries.__group__ = ['plot']
+except (NameError, AttributeError):
+    pass
 try:
     Qgs2DPlot.__virtual_methods__ = ['render', 'renderContent', 'interiorPlotArea']
     Qgs2DPlot.__overridden_methods__ = ['writeXml', 'readXml']
     Qgs2DPlot.__group__ = ['plot']
 except (NameError, AttributeError):
     pass
+try:
+    QgsXyPlotSeries.__overridden_methods__ = ['categories']
+    QgsXyPlotSeries.__group__ = ['plot']
+except (NameError, AttributeError):
+    pass
 try:
     Qgs2DXyPlot.__overridden_methods__ = ['writeXml', 'readXml', 'render', 'interiorPlotArea']
     Qgs2DXyPlot.__group__ = ['plot']
 except (NameError, AttributeError):
     pass
-try:
-    QgsAbstractPlotSeries.__group__ = ['plot']
-except (NameError, AttributeError):
-    pass
-try:
-    QgsXyPlotSeries.__group__ = ['plot']
-except (NameError, AttributeError):
-    pass
 try:
     QgsPlotData.__group__ = ['plot']
 except (NameError, AttributeError):

python/PyQt6/core/auto_generated/plot/qgschart.sip.in

@@ -0,0 +1,69 @@
+/************************************************************************
+ * This file has been generated automatically from                      *
+ *                                                                      *
+ * src/core/plot/qgschart.h                                             *
+ *                                                                      *
+ * Do not edit manually ! Edit header and run scripts/sipify.py again   *
+ ************************************************************************/
+
+
+
+
+class QgsBarChart : Qgs2DXyPlot
+{
+%Docstring(signature="appended")
+A simple bar chart class.
+
+.. warning::
+
+   This class is not considered stable API, and may change in future!
+
+.. versionadded:: 4.0
+%End
+
+%TypeHeaderCode
+#include "qgschart.h"
+%End
+  public:
+
+    QgsBarChart();
+    ~QgsBarChart();
+
+    virtual void renderContent( QgsRenderContext &context, const QRectF &plotArea, const QgsPlotData &plotData = QgsPlotData() );
+
+
+};
+
+
+class QgsLineChart : Qgs2DXyPlot
+{
+%Docstring(signature="appended")
+A simple line chart class.
+
+.. warning::
+
+   This class is not considered stable API, and may change in future!
+
+.. versionadded:: 4.0
+%End
+
+%TypeHeaderCode
+#include "qgschart.h"
+%End
+  public:
+
+    QgsLineChart();
+    ~QgsLineChart();
+
+    virtual void renderContent( QgsRenderContext &context, const QRectF &plotArea, const QgsPlotData &plotData = QgsPlotData() );
+
+
+};
+
+/************************************************************************
+ * This file has been generated automatically from                      *
+ *                                                                      *
+ * src/core/plot/qgschart.h                                             *
+ *                                                                      *
+ * Do not edit manually ! Edit header and run scripts/sipify.py again   *
+ ************************************************************************/

python/PyQt6/core/auto_generated/plot/qgsplot.sip.in

@@ -52,13 +52,16 @@ class QgsAbstractPlotSeries
   public:
 
     QgsAbstractPlotSeries();
-    ~QgsAbstractPlotSeries();
+    virtual ~QgsAbstractPlotSeries();
 
     QString name() const;
     void setName( const QString &name );
     QgsSymbol *symbol() const;
-    void setSymbol( QgsSymbol *symbol );
+    void setSymbol( QgsSymbol *symbol /Transfer/ );
+    virtual QList<QVariant> categories() const;
 
+  private:
+    QgsAbstractPlotSeries( const QgsAbstractPlotSeries &other );
 };
 
 class QgsXyPlotSeries : QgsAbstractPlotSeries
@@ -72,9 +75,14 @@ class QgsXyPlotSeries : QgsAbstractPlotSeries
     QgsXyPlotSeries();
     ~QgsXyPlotSeries();
 
+    virtual QList<QVariant> categories() const;
+
+
     void append( const QVariant &x, const double &y );
     void clear();
 
+  private:
+    QgsXyPlotSeries( const QgsXyPlotSeries &other );
 };
 
 class QgsPlotData
@@ -89,7 +97,7 @@ class QgsPlotData
     ~QgsPlotData();
 
     QList<QgsAbstractPlotSeries *> series() const;
-    void addSeries( QgsAbstractPlotSeries *series );
+    void addSeries( QgsAbstractPlotSeries *series /Transfer/ );
     void clearSeries();
 
 };

python/PyQt6/core/core_auto.sip

@@ -518,6 +518,7 @@
 %Include auto_generated/painting/qgspaintenginehack.sip
 %Include auto_generated/painting/qgspainting.sip
 %Include auto_generated/pdf/qgspdfrenderer.sip
+%Include auto_generated/plot/qgschart.sip
 %Include auto_generated/plot/qgsplot.sip
 %Include auto_generated/pointcloud/qgspointcloudattribute.sip
 %Include auto_generated/pointcloud/qgspointcloudattributebyramprenderer.sip

python/core/auto_additions/qgsplot.py

@@ -13,25 +13,27 @@ try:
     QgsPlot.__group__ = ['plot']
 except (NameError, AttributeError):
     pass
+try:
+    QgsAbstractPlotSeries.__virtual_methods__ = ['categories']
+    QgsAbstractPlotSeries.__group__ = ['plot']
+except (NameError, AttributeError):
+    pass
 try:
     Qgs2DPlot.__virtual_methods__ = ['render', 'renderContent', 'interiorPlotArea']
     Qgs2DPlot.__overridden_methods__ = ['writeXml', 'readXml']
     Qgs2DPlot.__group__ = ['plot']
 except (NameError, AttributeError):
     pass
+try:
+    QgsXyPlotSeries.__overridden_methods__ = ['categories']
+    QgsXyPlotSeries.__group__ = ['plot']
+except (NameError, AttributeError):
+    pass
 try:
     Qgs2DXyPlot.__overridden_methods__ = ['writeXml', 'readXml', 'render', 'interiorPlotArea']
     Qgs2DXyPlot.__group__ = ['plot']
 except (NameError, AttributeError):
     pass
-try:
-    QgsAbstractPlotSeries.__group__ = ['plot']
-except (NameError, AttributeError):
-    pass
-try:
-    QgsXyPlotSeries.__group__ = ['plot']
-except (NameError, AttributeError):
-    pass
 try:
     QgsPlotData.__group__ = ['plot']
 except (NameError, AttributeError):

python/core/auto_generated/plot/qgschart.sip.in

@@ -0,0 +1,69 @@
+/************************************************************************
+ * This file has been generated automatically from                      *
+ *                                                                      *
+ * src/core/plot/qgschart.h                                             *
+ *                                                                      *
+ * Do not edit manually ! Edit header and run scripts/sipify.py again   *
+ ************************************************************************/
+
+
+
+
+class QgsBarChart : Qgs2DXyPlot
+{
+%Docstring(signature="appended")
+A simple bar chart class.
+
+.. warning::
+
+   This class is not considered stable API, and may change in future!
+
+.. versionadded:: 4.0
+%End
+
+%TypeHeaderCode
+#include "qgschart.h"
+%End
+  public:
+
+    QgsBarChart();
+    ~QgsBarChart();
+
+    virtual void renderContent( QgsRenderContext &context, const QRectF &plotArea, const QgsPlotData &plotData = QgsPlotData() );
+
+
+};
+
+
+class QgsLineChart : Qgs2DXyPlot
+{
+%Docstring(signature="appended")
+A simple line chart class.
+
+.. warning::
+
+   This class is not considered stable API, and may change in future!
+
+.. versionadded:: 4.0
+%End
+
+%TypeHeaderCode
+#include "qgschart.h"
+%End
+  public:
+
+    QgsLineChart();
+    ~QgsLineChart();
+
+    virtual void renderContent( QgsRenderContext &context, const QRectF &plotArea, const QgsPlotData &plotData = QgsPlotData() );
+
+
+};
+
+/************************************************************************
+ * This file has been generated automatically from                      *
+ *                                                                      *
+ * src/core/plot/qgschart.h                                             *
+ *                                                                      *
+ * Do not edit manually ! Edit header and run scripts/sipify.py again   *
+ ************************************************************************/

python/core/auto_generated/plot/qgsplot.sip.in

@@ -52,13 +52,16 @@ class QgsAbstractPlotSeries
   public:
 
     QgsAbstractPlotSeries();
-    ~QgsAbstractPlotSeries();
+    virtual ~QgsAbstractPlotSeries();
 
     QString name() const;
     void setName( const QString &name );
     QgsSymbol *symbol() const;
-    void setSymbol( QgsSymbol *symbol );
+    void setSymbol( QgsSymbol *symbol /Transfer/ );
+    virtual QList<QVariant> categories() const;
 
+  private:
+    QgsAbstractPlotSeries( const QgsAbstractPlotSeries &other );
 };
 
 class QgsXyPlotSeries : QgsAbstractPlotSeries
@@ -72,9 +75,14 @@ class QgsXyPlotSeries : QgsAbstractPlotSeries
     QgsXyPlotSeries();
     ~QgsXyPlotSeries();
 
+    virtual QList<QVariant> categories() const;
+
+
     void append( const QVariant &x, const double &y );
     void clear();
 
+  private:
+    QgsXyPlotSeries( const QgsXyPlotSeries &other );
 };
 
 class QgsPlotData
@@ -89,7 +97,7 @@ class QgsPlotData
     ~QgsPlotData();
 
     QList<QgsAbstractPlotSeries *> series() const;
-    void addSeries( QgsAbstractPlotSeries *series );
+    void addSeries( QgsAbstractPlotSeries *series /Transfer/ );
     void clearSeries();
 
 };

python/core/core_auto.sip

@@ -518,6 +518,7 @@
 %Include auto_generated/painting/qgspaintenginehack.sip
 %Include auto_generated/painting/qgspainting.sip
 %Include auto_generated/pdf/qgspdfrenderer.sip
+%Include auto_generated/plot/qgschart.sip
 %Include auto_generated/plot/qgsplot.sip
 %Include auto_generated/pointcloud/qgspointcloudattribute.sip
 %Include auto_generated/pointcloud/qgspointcloudattributebyramprenderer.sip

src/core/CMakeLists.txt

@@ -90,6 +90,7 @@ set(QGIS_CORE_SRCS
   gps/qgssatelliteinformation.cpp
   gps/qgsvectorlayergpslogger.cpp
 
+  plot/qgschart.cpp
   plot/qgsplot.cpp
 
   symbology/qgs25drenderer.cpp
@@ -1739,6 +1740,7 @@ set(QGIS_CORE_HDRS
 
   pdf/qgspdfrenderer.h
 
+  plot/qgschart.h
   plot/qgsplot.h
 
   pointcloud/qgspointcloudattribute.h

src/core/plot/qgschart.cpp

@@ -0,0 +1,163 @@
+/***************************************************************************
+                         qgsplot.cpp
+                         ---------------
+    begin                : March 2022
+    copyright            : (C) 2022 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 "qgschart.h"
+#include "qgsexpressioncontextutils.h"
+#include "qgssymbol.h"
+#include "qgssymbollayer.h"
+#include "qgsfillsymbol.h"
+#include "qgslinesymbol.h"
+
+void QgsBarChart::renderContent( QgsRenderContext &context, const QRectF &plotArea, const QgsPlotData &plotData )
+{
+  const QList<QgsAbstractPlotSeries *> seriesList = plotData.series();
+  if ( seriesList.isEmpty() )
+  {
+    return;
+  }
+
+  const QList<QVariant> categories = seriesList.at( 0 )->categories();
+  if ( categories.isEmpty() )
+  {
+    return;
+  }
+
+  QgsExpressionContextScope *chartScope = new QgsExpressionContextScope( QStringLiteral( "chart" ) );
+  const QgsExpressionContextScopePopper scopePopper( context.expressionContext(), chartScope );
+
+  context.painter()->save();
+  context.painter()->setClipRect( plotArea );
+
+  const double xScale = plotArea.width() / ( xMaximum() - xMinimum() );
+  const double yScale = plotArea.height() / ( yMaximum() - yMinimum() );
+  const double categoriesWidth = plotArea.width() / categories.size();
+  const double barsWidth = categoriesWidth / 2;
+  const double barWidth = barsWidth / seriesList.size();
+  int seriesIndex = 0;
+  for ( const QgsAbstractPlotSeries *series : seriesList )
+  {
+    QgsFillSymbol *symbol = dynamic_cast<QgsFillSymbol *>( series->symbol() );
+    if ( !symbol )
+    {
+      continue;
+    }
+    symbol->startRender( context );
+
+    const double barStartAdjustement = -( barsWidth / 2 ) + barWidth * seriesIndex;
+    if ( const QgsXyPlotSeries *xySeries = dynamic_cast<const QgsXyPlotSeries *>( series ) )
+    {
+      const QList<std::pair<QVariant, double>> data = xySeries->data();
+      for ( const std::pair<QVariant, double> &pair : data )
+      {
+        double x, y;
+        if ( xAxis().type() == Qgis::PlotAxisType::ValueType )
+        {
+          x = ( pair.first.toDouble() ) * xScale + barStartAdjustement;
+        }
+        else if ( xAxis().type() == Qgis::PlotAxisType::CategoryType )
+        {
+          x = ( categoriesWidth * categories.indexOf( pair.first ) ) + ( categoriesWidth / 2 ) + barStartAdjustement;
+        }
+        y = ( pair.second - yMinimum() ) * yScale;
+
+        const double zero = ( 0.0 - yMinimum() ) * yScale;
+        const QPoint topLeft( plotArea.left() + x,
+                              plotArea.y() + plotArea.height() - y );
+        const QPoint bottomRight( plotArea.left() + x + barWidth,
+                                  plotArea.y() + plotArea.height() - zero );
+
+        chartScope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "chart_value" ), pair.second, true ) );
+        symbol->renderPolygon( QPolygonF( QRectF( topLeft, bottomRight ) ), nullptr, nullptr, context );
+      }
+    }
+
+    symbol->stopRender( context );
+    seriesIndex++;
+  }
+
+  context.painter()->restore();
+}
+
+void QgsLineChart::renderContent( QgsRenderContext &context, const QRectF &plotArea, const QgsPlotData &plotData )
+{
+  const QList<QgsAbstractPlotSeries *> seriesList = plotData.series();
+  if ( seriesList.isEmpty() )
+  {
+    return;
+  }
+
+  const QList<QVariant> categories = seriesList.at( 0 )->categories();
+  if ( categories.isEmpty() )
+  {
+    return;
+  }
+
+  QgsExpressionContextScope *chartScope = new QgsExpressionContextScope( QStringLiteral( "chart" ) );
+  const QgsExpressionContextScopePopper scopePopper( context.expressionContext(), chartScope );
+
+  context.painter()->save();
+  context.painter()->setClipRect( plotArea );
+
+  const double xScale = plotArea.width() / ( xMaximum() - xMinimum() );
+  const double yScale = plotArea.height() / ( yMaximum() - yMinimum() );
+  const double categoriesWidth = plotArea.width() / categories.size();
+  int seriesIndex = 0;
+  for ( const QgsAbstractPlotSeries *series : seriesList )
+  {
+    QgsLineSymbol *symbol = dynamic_cast<QgsLineSymbol *>( series->symbol() );
+    if ( !symbol )
+    {
+      continue;
+    }
+    symbol->startRender( context );
+
+    if ( const QgsXyPlotSeries *xySeries = dynamic_cast<const QgsXyPlotSeries *>( series ) )
+    {
+      const QList<std::pair<QVariant, double>> data = xySeries->data();
+      QVector<QPointF> points;
+      QList<double> values;
+      points.fill( QPointF(), xAxis().type() == Qgis::PlotAxisType::ValueType ? data.size() : categories.size() );
+      int dataIndex = 0;
+      for ( const std::pair<QVariant, double> &pair : data )
+      {
+        double x, y;
+        if ( xAxis().type() == Qgis::PlotAxisType::ValueType )
+        {
+          x = ( pair.first.toDouble() ) * xScale;
+        }
+        else if ( xAxis().type() == Qgis::PlotAxisType::CategoryType )
+        {
+          x = ( categoriesWidth * categories.indexOf( pair.first ) ) + ( categoriesWidth / 2 );
+        }
+        y = ( pair.second - yMinimum() ) * yScale;
+
+        values << pair.second;
+        points.replace( xAxis().type() == Qgis::PlotAxisType::ValueType ? dataIndex : categories.indexOf( pair.first ), QPointF( plotArea.x() + x,
+                        plotArea.y() + plotArea.height() - y ) );
+        dataIndex++;
+      }
+
+      chartScope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "chart_value" ), QVariant::fromValue( values ), true ) );
+      symbol->renderPolyline( QPolygonF( points ), nullptr, context );
+    }
+
+    symbol->stopRender( context );
+    seriesIndex++;
+  }
+
+  context.painter()->restore();
+}

src/core/plot/qgschart.h

@@ -0,0 +1,70 @@
+/***************************************************************************
+                         qgschart.h
+                         ---------------
+    begin                : June 2025
+    copyright            : (C) 2025 by Mathieu
+    email                : mathieu at opengis dot ch
+ ***************************************************************************/
+
+/***************************************************************************
+ *                                                                         *
+ *   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 QGSCHART_H
+#define QGSCHART_H
+
+#include "qgis_core.h"
+#include "qgis_sip.h"
+#include "qgsplot.h"
+
+
+/**
+ * \brief A simple bar chart class.
+ *
+ * \warning This class is not considered stable API, and may change in future!
+ *
+ * \ingroup core
+ * \since QGIS 4.0
+ */
+class CORE_EXPORT QgsBarChart : public Qgs2DXyPlot
+{
+  public:
+
+    QgsBarChart() = default;
+    ~QgsBarChart() = default;
+
+    void renderContent( QgsRenderContext &context, const QRectF &plotArea, const QgsPlotData &plotData = QgsPlotData() ) override;
+
+  private:
+
+
+};
+
+
+/**
+ * \brief A simple line chart class.
+ *
+ * \warning This class is not considered stable API, and may change in future!
+ *
+ * \ingroup core
+ * \since QGIS 4.0
+ */
+class CORE_EXPORT QgsLineChart : public Qgs2DXyPlot
+{
+  public:
+
+    QgsLineChart() = default;
+    ~QgsLineChart() = default;
+
+    void renderContent( QgsRenderContext &context, const QRectF &plotArea, const QgsPlotData &plotData = QgsPlotData() ) override;
+
+  private:
+
+
+};
+
+#endif

src/core/plot/qgsplot.cpp

@@ -334,10 +334,18 @@ void Qgs2DXyPlot::render( QgsRenderContext &context, const QgsPlotData &plotData
 
   QgsNumericFormatContext numericContext;
 
+  // categories
+  QList<QVariant> categories;
+  const QList<QgsAbstractPlotSeries *> seriesList = plotData.series();
+  if ( !seriesList.isEmpty() )
+  {
+    categories = seriesList.at( 0 )->categories();
+  }
+
   // calculate text metrics
   double maxYAxisLabelWidth = 0;
   plotScope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "plot_axis" ), QStringLiteral( "y" ), true ) );
-  if ( mYAxis.labelInterval() > 0 )
+  if ( mYAxis.type() == Qgis::PlotAxisType::ValueType && mYAxis.labelInterval() > 0 )
   {
     for ( double currentY = firstYLabel; ; currentY += mYAxis.labelInterval() )
     {
@@ -374,6 +382,14 @@ void Qgs2DXyPlot::render( QgsRenderContext &context, const QgsPlotData &plotData
         break;
     }
   }
+  else if ( mYAxis.type() == Qgis::PlotAxisType::CategoryType )
+  {
+    for ( int i = 0; i < categories.size(); i++ )
+    {
+      const QString text = categories.at( i ).toString();
+      maxYAxisLabelWidth = std::max( maxYAxisLabelWidth, QgsTextRenderer::textWidth( context, mYAxis.textFormat(), { text } ) );
+    }
+  }
 
   const double chartAreaLeft = plotArea.left();
   const double chartAreaRight = plotArea.right();
@@ -398,139 +414,180 @@ void Qgs2DXyPlot::render( QgsRenderContext &context, const QgsPlotData &plotData
   // grid lines
 
   // x
-  plotScope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "plot_axis" ), QStringLiteral( "x" ), true ) );
-  double nextMajorXGrid = firstMajorXGrid;
-  int objectNumber = 0;
-  for ( double currentX = firstMinorXGrid; objectNumber < MAX_OBJECTS && ( currentX <= mMaxX && !qgsDoubleNear( currentX, mMaxX, xTolerance ) ); currentX += mXAxis.gridIntervalMinor(), ++objectNumber )
+  if ( mXAxis.type() == Qgis::PlotAxisType::ValueType )
   {
-    bool isMinor = true;
-    if ( qgsDoubleNear( currentX, nextMajorXGrid, xTolerance ) )
+    plotScope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "plot_axis" ), QStringLiteral( "x" ), true ) );
+    double nextMajorXGrid = firstMajorXGrid;
+    int objectNumber = 0;
+    for ( double currentX = firstMinorXGrid; objectNumber < MAX_OBJECTS && ( currentX <= mMaxX && !qgsDoubleNear( currentX, mMaxX, xTolerance ) ); currentX += mXAxis.gridIntervalMinor(), ++objectNumber )
     {
-      isMinor = false;
-      nextMajorXGrid += mXAxis.gridIntervalMajor();
+      bool isMinor = true;
+      if ( qgsDoubleNear( currentX, nextMajorXGrid, xTolerance ) )
+      {
+        isMinor = false;
+        nextMajorXGrid += mXAxis.gridIntervalMajor();
+      }
+
+      plotScope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "plot_axis_value" ), currentX, true ) );
+
+      QgsLineSymbol *currentGridSymbol = isMinor ? mXAxis.gridMinorSymbol() : mXAxis.gridMajorSymbol();
+      currentGridSymbol->renderPolyline( QPolygonF(
+                                           QVector<QPointF>
+      {
+        QPointF( ( currentX - mMinX ) * xScale + chartAreaLeft, chartAreaBottom ),
+        QPointF( ( currentX - mMinX ) * xScale + chartAreaLeft, chartAreaTop )
+      } ), nullptr, context );
     }
-
-    plotScope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "plot_axis_value" ), currentX, true ) );
-
-    QgsLineSymbol *currentGridSymbol = isMinor ? mXAxis.gridMinorSymbol() : mXAxis.gridMajorSymbol();
-    currentGridSymbol->renderPolyline( QPolygonF(
-                                         QVector<QPointF>
-    {
-      QPointF( ( currentX - mMinX ) * xScale + chartAreaLeft, chartAreaBottom ),
-      QPointF( ( currentX - mMinX ) * xScale + chartAreaLeft, chartAreaTop )
-    } ), nullptr, context );
   }
 
   // y
-  plotScope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "plot_axis" ), QStringLiteral( "y" ), true ) );
-  double nextMajorYGrid = firstMajorYGrid;
-  objectNumber = 0;
-  for ( double currentY = firstMinorYGrid; objectNumber < MAX_OBJECTS && ( currentY <= mMaxY && !qgsDoubleNear( currentY, mMaxY, yTolerance ) ); currentY += mYAxis.gridIntervalMinor(), ++objectNumber )
+  if ( mYAxis.type() == Qgis::PlotAxisType::ValueType )
   {
-    bool isMinor = true;
-    if ( qgsDoubleNear( currentY, nextMajorYGrid, yTolerance ) )
+    plotScope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "plot_axis" ), QStringLiteral( "y" ), true ) );
+    double nextMajorYGrid = firstMajorYGrid;
+    int objectNumber = 0;
+    for ( double currentY = firstMinorYGrid; objectNumber < MAX_OBJECTS && ( currentY <= mMaxY && !qgsDoubleNear( currentY, mMaxY, yTolerance ) ); currentY += mYAxis.gridIntervalMinor(), ++objectNumber )
     {
-      isMinor = false;
-      nextMajorYGrid += mYAxis.gridIntervalMajor();
+      bool isMinor = true;
+      if ( qgsDoubleNear( currentY, nextMajorYGrid, yTolerance ) )
+      {
+        isMinor = false;
+        nextMajorYGrid += mYAxis.gridIntervalMajor();
+      }
+
+      plotScope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "plot_axis_value" ), currentY, true ) );
+
+      QgsLineSymbol *currentGridSymbol = isMinor ? mYAxis.gridMinorSymbol() : mYAxis.gridMajorSymbol();
+      currentGridSymbol->renderPolyline( QPolygonF(
+                                           QVector<QPointF>
+      {
+        QPointF( chartAreaLeft, chartAreaBottom - ( currentY - mMinY ) * yScale ),
+        QPointF( chartAreaRight, chartAreaBottom - ( currentY - mMinY ) * yScale )
+      } ), nullptr, context );
     }
-
-    plotScope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "plot_axis_value" ), currentY, true ) );
-
-    QgsLineSymbol *currentGridSymbol = isMinor ? mYAxis.gridMinorSymbol() : mYAxis.gridMajorSymbol();
-    currentGridSymbol->renderPolyline( QPolygonF(
-                                         QVector<QPointF>
-    {
-      QPointF( chartAreaLeft, chartAreaBottom - ( currentY - mMinY ) * yScale ),
-      QPointF( chartAreaRight, chartAreaBottom - ( currentY - mMinY ) * yScale )
-    } ), nullptr, context );
   }
 
   // axis labels
 
   // x
-  plotScope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "plot_axis" ), QStringLiteral( "x" ), true ) );
-  objectNumber = 0;
-  if ( mXAxis.labelInterval() > 0 )
+  if ( mXAxis.type() == Qgis::PlotAxisType::ValueType )
   {
-    for ( double currentX = firstXLabel; ; currentX += mXAxis.labelInterval(), ++objectNumber )
+    plotScope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "plot_axis" ), QStringLiteral( "x" ), true ) );
+    int objectNumber = 0;
+    if ( mXAxis.labelInterval() > 0 )
     {
-      const bool hasMoreLabels = objectNumber + 1 < MAX_OBJECTS && ( currentX + mXAxis.labelInterval() <= mMaxX || qgsDoubleNear( currentX + mXAxis.labelInterval(), mMaxX, xTolerance ) );
-      plotScope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "plot_axis_value" ), currentX, true ) );
-      QString text = mXAxis.numericFormat()->formatDouble( currentX, numericContext );
-      switch ( mXAxis.labelSuffixPlacement() )
+      for ( double currentX = firstXLabel; ; currentX += mXAxis.labelInterval(), ++objectNumber )
       {
-        case Qgis::PlotAxisSuffixPlacement::NoLabels:
-          break;
+        const bool hasMoreLabels = objectNumber + 1 < MAX_OBJECTS && ( currentX + mXAxis.labelInterval() <= mMaxX || qgsDoubleNear( currentX + mXAxis.labelInterval(), mMaxX, xTolerance ) );
+        plotScope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "plot_axis_value" ), currentX, true ) );
+        QString text = mXAxis.numericFormat()->formatDouble( currentX, numericContext );
+        switch ( mXAxis.labelSuffixPlacement() )
+        {
+          case Qgis::PlotAxisSuffixPlacement::NoLabels:
+            break;
 
-        case Qgis::PlotAxisSuffixPlacement::EveryLabel:
-          text += xAxisSuffix;
-          break;
-
-        case Qgis::PlotAxisSuffixPlacement::FirstLabel:
-          if ( objectNumber == 0 )
+          case Qgis::PlotAxisSuffixPlacement::EveryLabel:
             text += xAxisSuffix;
-          break;
+            break;
 
-        case Qgis::PlotAxisSuffixPlacement::LastLabel:
-          if ( !hasMoreLabels )
-            text += xAxisSuffix;
-          break;
+          case Qgis::PlotAxisSuffixPlacement::FirstLabel:
+            if ( objectNumber == 0 )
+              text += xAxisSuffix;
+            break;
 
-        case Qgis::PlotAxisSuffixPlacement::FirstAndLastLabels:
-          if ( objectNumber == 0 || !hasMoreLabels )
-            text += xAxisSuffix;
+          case Qgis::PlotAxisSuffixPlacement::LastLabel:
+            if ( !hasMoreLabels )
+              text += xAxisSuffix;
+            break;
+
+          case Qgis::PlotAxisSuffixPlacement::FirstAndLastLabels:
+            if ( objectNumber == 0 || !hasMoreLabels )
+              text += xAxisSuffix;
+            break;
+        }
+
+        QgsTextRenderer::drawText( QPointF( ( currentX - mMinX ) * xScale + chartAreaLeft, mSize.height() - context.convertToPainterUnits( mMargins.bottom(), Qgis::RenderUnit::Millimeters ) ),
+                                   0, Qgis::TextHorizontalAlignment::Center, { text }, context, mXAxis.textFormat() );
+        if ( !hasMoreLabels )
           break;
       }
-
-      QgsTextRenderer::drawText( QPointF( ( currentX - mMinX ) * xScale + chartAreaLeft, mSize.height() - context.convertToPainterUnits( mMargins.bottom(), Qgis::RenderUnit::Millimeters ) ),
+    }
+  }
+  else if ( mXAxis.type() == Qgis::PlotAxisType::CategoryType )
+  {
+    plotScope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "plot_axis" ), QStringLiteral( "x" ), true ) );
+    const double categoryWidth = plotArea.width() / categories.size();
+    for ( int i = 0; i < categories.size(); i++ )
+    {
+      const double currentX = ( i * categoryWidth ) + categoryWidth / 2.0;
+      plotScope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "plot_axis_value" ), categories.at( i ), true ) );
+      const QString text = categories.at( i ).toString();
+      QgsTextRenderer::drawText( QPointF( currentX + chartAreaLeft, mSize.height() - context.convertToPainterUnits( mMargins.bottom(), Qgis::RenderUnit::Millimeters ) ),
                                  0, Qgis::TextHorizontalAlignment::Center, { text }, context, mXAxis.textFormat() );
-      if ( !hasMoreLabels )
-        break;
     }
   }
 
   // y
-  plotScope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "plot_axis" ), QStringLiteral( "y" ), true ) );
-  objectNumber = 0;
-  if ( mYAxis.labelInterval() > 0 )
+  if ( mYAxis.type() == Qgis::PlotAxisType::ValueType )
   {
-    for ( double currentY = firstYLabel; ; currentY += mYAxis.labelInterval(), ++objectNumber )
+    plotScope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "plot_axis" ), QStringLiteral( "y" ), true ) );
+    int objectNumber = 0;
+    if ( mYAxis.labelInterval() > 0 )
     {
-      const bool hasMoreLabels = objectNumber + 1 < MAX_OBJECTS && ( currentY + mYAxis.labelInterval() <= mMaxY || qgsDoubleNear( currentY + mYAxis.labelInterval(), mMaxY, yTolerance ) );
-      plotScope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "plot_axis_value" ), currentY, true ) );
-      QString text = mYAxis.numericFormat()->formatDouble( currentY, numericContext );
-      switch ( mYAxis.labelSuffixPlacement() )
+      for ( double currentY = firstYLabel; ; currentY += mYAxis.labelInterval(), ++objectNumber )
       {
-        case Qgis::PlotAxisSuffixPlacement::NoLabels:
-          break;
+        const bool hasMoreLabels = objectNumber + 1 < MAX_OBJECTS && ( currentY + mYAxis.labelInterval() <= mMaxY || qgsDoubleNear( currentY + mYAxis.labelInterval(), mMaxY, yTolerance ) );
+        plotScope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "plot_axis_value" ), currentY, true ) );
+        QString text = mYAxis.numericFormat()->formatDouble( currentY, numericContext );
+        switch ( mYAxis.labelSuffixPlacement() )
+        {
+          case Qgis::PlotAxisSuffixPlacement::NoLabels:
+            break;
 
-        case Qgis::PlotAxisSuffixPlacement::EveryLabel:
-          text += yAxisSuffix;
-          break;
-
-        case Qgis::PlotAxisSuffixPlacement::FirstLabel:
-          if ( objectNumber == 0 )
+          case Qgis::PlotAxisSuffixPlacement::EveryLabel:
             text += yAxisSuffix;
-          break;
+            break;
 
-        case Qgis::PlotAxisSuffixPlacement::LastLabel:
-          if ( !hasMoreLabels )
-            text += yAxisSuffix;
-          break;
+          case Qgis::PlotAxisSuffixPlacement::FirstLabel:
+            if ( objectNumber == 0 )
+              text += yAxisSuffix;
+            break;
 
-        case Qgis::PlotAxisSuffixPlacement::FirstAndLastLabels:
-          if ( objectNumber == 0 || !hasMoreLabels )
-            text += yAxisSuffix;
+          case Qgis::PlotAxisSuffixPlacement::LastLabel:
+            if ( !hasMoreLabels )
+              text += yAxisSuffix;
+            break;
+
+          case Qgis::PlotAxisSuffixPlacement::FirstAndLastLabels:
+            if ( objectNumber == 0 || !hasMoreLabels )
+              text += yAxisSuffix;
+            break;
+        }
+
+        const double height = QgsTextRenderer::textHeight( context, mYAxis.textFormat(), { text } );
+        QgsTextRenderer::drawText( QPointF(
+                                     maxYAxisLabelWidth + context.convertToPainterUnits( mMargins.left(), Qgis::RenderUnit::Millimeters ),
+                                     chartAreaBottom - ( currentY - mMinY ) * yScale + height / 2 ),
+                                   0, Qgis::TextHorizontalAlignment::Right, { text }, context, mYAxis.textFormat(), false );
+        if ( !hasMoreLabels )
           break;
       }
-
+    }
+  }
+  else if ( mYAxis.type() == Qgis::PlotAxisType::CategoryType )
+  {
+    plotScope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "plot_axis" ), QStringLiteral( "y" ), true ) );
+    const double categoryHeight = plotArea.height() / categories.size();
+    for ( int i = 0; i < categories.size(); i++ )
+    {
+      const double currentY = ( i * categoryHeight ) + categoryHeight / 2.0;
+      plotScope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "plot_axis_value" ), categories.at( i ), true ) );
+      const QString text = categories.at( i ).toString();
       const double height = QgsTextRenderer::textHeight( context, mYAxis.textFormat(), { text } );
       QgsTextRenderer::drawText( QPointF(
                                    maxYAxisLabelWidth + context.convertToPainterUnits( mMargins.left(), Qgis::RenderUnit::Millimeters ),
-                                   chartAreaBottom - ( currentY - mMinY ) * yScale + height / 2 ),
+                                   chartAreaBottom - currentY + height / 2 ),
                                  0, Qgis::TextHorizontalAlignment::Right, { text }, context, mYAxis.textFormat(), false );
-      if ( !hasMoreLabels )
-        break;
     }
   }
 
@@ -906,19 +963,33 @@ void QgsAbstractPlotSeries::setName( const QString &name )
 
 QgsSymbol *QgsAbstractPlotSeries::symbol() const
 {
-  return mSymbol;
+  return mSymbol.get();
 }
 
 void QgsAbstractPlotSeries::setSymbol( QgsSymbol *symbol )
 {
-  delete mSymbol;
-  mSymbol = symbol;
+  mSymbol.reset( symbol );
+}
+
+QList<QVariant> QgsAbstractPlotSeries::categories() const
+{
+  return QList<QVariant>();
 }
 
 //
 // QgsXyPlotSeries
 //
 
+QList<QVariant> QgsXyPlotSeries::categories() const
+{
+  QList<QVariant> categories;
+  for ( const std::pair<QVariant, double> &pair : std::as_const( mData ) )
+  {
+    categories << pair.first;
+  }
+  return categories;
+}
+
 QList<std::pair<QVariant, double>> QgsXyPlotSeries::data() const
 {
   return mData;

src/core/plot/qgsplot.h

@@ -68,17 +68,21 @@ class CORE_EXPORT QgsAbstractPlotSeries
   public:
 
     QgsAbstractPlotSeries() = default;
-    ~QgsAbstractPlotSeries() = default;
+    virtual ~QgsAbstractPlotSeries() = default;
 
     QString name() const;
     void setName( const QString &name );
     QgsSymbol *symbol() const;
-    void setSymbol( QgsSymbol *symbol );
+    void setSymbol( QgsSymbol *symbol SIP_TRANSFER );
+    virtual QList<QVariant> categories() const;
 
   private:
+#ifdef SIP_RUN
+    QgsAbstractPlotSeries( const QgsAbstractPlotSeries &other );
+#endif
 
     QString mName;
-    QgsSymbol *mSymbol = nullptr;
+    std::unique_ptr<QgsSymbol> mSymbol;
 };
 
 class CORE_EXPORT QgsXyPlotSeries : public QgsAbstractPlotSeries
@@ -88,11 +92,16 @@ class CORE_EXPORT QgsXyPlotSeries : public QgsAbstractPlotSeries
     QgsXyPlotSeries() = default;
     ~QgsXyPlotSeries() = default;
 
+    QList<QVariant> categories() const override;
+
     QList<std::pair<QVariant, double>> data() const SIP_SKIP;
     void append( const QVariant &x, const double &y );
     void clear();
 
   private:
+#ifdef SIP_RUN
+    QgsXyPlotSeries( const QgsXyPlotSeries &other );
+#endif
 
     QList<std::pair<QVariant, double>> mData;
 };
@@ -105,7 +114,7 @@ class CORE_EXPORT QgsPlotData
     ~QgsPlotData();
 
     QList<QgsAbstractPlotSeries *> series() const;
-    void addSeries( QgsAbstractPlotSeries *series );
+    void addSeries( QgsAbstractPlotSeries *series SIP_TRANSFER );
     void clearSeries();
 
   private: