Make axes ownership more useful

Chart can now own multiple axes while showing only one.
Default axes are no longer modifiable by users.

Task-number: QTRD-2212
Change-Id: I028f0d7539dbbf6e3474680290c7ec6bba5a4223
Reviewed-by: Tomi Korpipää <tomi.korpipaa@digia.com>

26 files changed, 497 insertions, 141 deletions

diff --git a/src/datavis3d/axis/qabstractaxis.cpp b/src/datavis3d/axis/qabstractaxis.cpp
index 5129dfab..0b233903 100644
--- a/src/datavis3d/axis/qabstractaxis.cpp
+++ b/src/datavis3d/axis/qabstractaxis.cpp
@@ -124,7 +124,8 @@ QAbstractAxisPrivate::QAbstractAxisPrivate(QAbstractAxis *q, QAbstractAxis::Axis
     : QObject(0),
       q_ptr(q),
       m_orientation(QAbstractAxis::AxisOrientationNone),
-      m_type(type)
+      m_type(type),
+      m_isDefaultAxis(false)
 {
 }
 
diff --git a/src/datavis3d/axis/qabstractaxis.h b/src/datavis3d/axis/qabstractaxis.h
index aac2ee30..e2c127ad 100644
--- a/src/datavis3d/axis/qabstractaxis.h
+++ b/src/datavis3d/axis/qabstractaxis.h
@@ -80,6 +80,7 @@ private:
     Q_DISABLE_COPY(QAbstractAxis)
 
     friend class Abstract3DController;
+    friend class Bars3dController;
 };
 
 QT_DATAVIS3D_END_NAMESPACE
diff --git a/src/datavis3d/axis/qabstractaxis_p.h b/src/datavis3d/axis/qabstractaxis_p.h
index 5b73ce17..6422868f 100644
--- a/src/datavis3d/axis/qabstractaxis_p.h
+++ b/src/datavis3d/axis/qabstractaxis_p.h
@@ -28,6 +28,7 @@
 
 #include "datavis3dglobal_p.h"
 #include "qabstractaxis.h"
+#include "abstract3dcontroller_p.h"
 
 #ifndef QABSTRACTAXIS_P_H
 #define QABSTRACTAXIS_P_H
@@ -43,6 +44,9 @@ public:
 
     void setOrientation(QAbstractAxis::AxisOrientation orientation);
 
+    inline bool isDefaultAxis() { return m_isDefaultAxis; }
+    inline void setDefaultAxis(bool isDefault) { m_isDefaultAxis = isDefault; }
+
 protected:
     virtual void updateLabels();
 
@@ -52,6 +56,7 @@ protected:
     QStringList m_labels;
     QAbstractAxis::AxisOrientation m_orientation;
     QAbstractAxis::AxisType m_type;
+    bool m_isDefaultAxis;
 
     friend class QAbstractAxis;
     friend class QValueAxis;
diff --git a/src/datavis3d/axis/qcategoryaxis.h b/src/datavis3d/axis/qcategoryaxis.h
index d162d34b..ab82e8d6 100644
--- a/src/datavis3d/axis/qcategoryaxis.h
+++ b/src/datavis3d/axis/qcategoryaxis.h
@@ -35,7 +35,7 @@ class QT_DATAVIS3D_EXPORT QCategoryAxis : public QAbstractAxis
 
 public:
     explicit QCategoryAxis(QObject *parent = 0);
-    ~QCategoryAxis();
+    virtual ~QCategoryAxis();
 
     QStringList categoryLabels() const;
 
diff --git a/src/datavis3d/axis/qvalueaxis.cpp b/src/datavis3d/axis/qvalueaxis.cpp
index 67bb9a38..9520cacd 100644
--- a/src/datavis3d/axis/qvalueaxis.cpp
+++ b/src/datavis3d/axis/qvalueaxis.cpp
@@ -219,7 +219,9 @@ QValueAxisPrivate::QValueAxisPrivate(QValueAxis *q)
       m_max(10.0),
       m_segmentCount(5),
       m_subSegmentCount(1),
-      m_autoAdjust(true)
+      m_autoAdjust(true),
+      m_labelFormat(Utils::defaultLabelFormat()),
+      m_labelsDirty(true)
 {
 }
 
@@ -307,9 +309,6 @@ void QValueAxisPrivate::updateLabels()
     qreal segmentStep = (m_max - m_min) / m_segmentCount;
 
     QString formatString(m_labelFormat);
-    if (formatString.isEmpty())
-        formatString = Utils::defaultLabelFormat();
-
     Utils::ParamType paramType = Utils::findFormatParamType(formatString);
     QByteArray formatArray = formatString.toUtf8();
 
diff --git a/src/datavis3d/axis/qvalueaxis.h b/src/datavis3d/axis/qvalueaxis.h
index 6bc84c15..1bffcb15 100644
--- a/src/datavis3d/axis/qvalueaxis.h
+++ b/src/datavis3d/axis/qvalueaxis.h
@@ -37,7 +37,7 @@ class QT_DATAVIS3D_EXPORT QValueAxis : public QAbstractAxis
 
 public:
     explicit QValueAxis(QObject *parent = 0);
-    ~QValueAxis();
+    virtual ~QValueAxis();
 
     qreal min() const;
     qreal max() const;
diff --git a/src/datavis3d/data/barrenderitem_p.h b/src/datavis3d/data/barrenderitem_p.h
index 0b7dc639..67e1e256 100644
--- a/src/datavis3d/data/barrenderitem_p.h
+++ b/src/datavis3d/data/barrenderitem_p.h
@@ -77,14 +77,12 @@ protected:
 
 void BarRenderItem::setValue(qreal value)
 {
-    if (m_value != value) {
-        m_value = value;
-         // Force reformatting on next access by setting label string to null string
-        if (!m_sliceLabel.isNull())
-            setSliceLabel(QString());
-        if (!m_selectionLabel.isNull())
-            setSelectionLabel(QString());
-    }
+    m_value = value;
+     // Force reformatting on next access by setting label string to null string
+    if (!m_sliceLabel.isNull())
+        setSliceLabel(QString());
+    if (!m_selectionLabel.isNull())
+        setSelectionLabel(QString());
 }
 
 typedef QVector<BarRenderItem> BarRenderItemRow;
diff --git a/src/datavis3d/engine/abstract3dcontroller.cpp b/src/datavis3d/engine/abstract3dcontroller.cpp
index de80bd41..06d81021 100644
--- a/src/datavis3d/engine/abstract3dcontroller.cpp
+++ b/src/datavis3d/engine/abstract3dcontroller.cpp
@@ -20,6 +20,7 @@
 #include "camerahelper_p.h"
 #include "qabstractaxis_p.h"
 #include "qvalueaxis.h"
+#include "qcategoryaxis.h"
 #include "abstract3drenderer_p.h"
 
 #if defined(Q_OS_ANDROID)
@@ -63,9 +64,8 @@ Abstract3DController::Abstract3DController(QRect boundRect, QObject *parent) :
 Abstract3DController::~Abstract3DController()
 {
     delete m_cameraHelper;
-    delete m_axisX;
-    delete m_axisY;
-    delete m_axisZ;
+
+    // Attached axes are children, so no need to explicitly delete them
 }
 
 void Abstract3DController::setRenderer(Abstract3DRenderer *renderer)
@@ -383,6 +383,8 @@ void Abstract3DController::setAxisX(QAbstractAxis *axis)
 
 QAbstractAxis *Abstract3DController::axisX()
 {
+    if (m_axisX->d_ptr->isDefaultAxis())
+        return 0;
     return m_axisX;
 }
 
@@ -393,6 +395,8 @@ void Abstract3DController::setAxisY(QAbstractAxis *axis)
 
 QAbstractAxis *Abstract3DController::axisY()
 {
+    if (m_axisY->d_ptr->isDefaultAxis())
+        return 0;
     return m_axisY;
 }
 
@@ -403,9 +407,57 @@ void Abstract3DController::setAxisZ(QAbstractAxis *axis)
 
 QAbstractAxis *Abstract3DController::axisZ()
 {
+    if (m_axisZ->d_ptr->isDefaultAxis())
+        return 0;
     return m_axisZ;
 }
 
+void Abstract3DController::addAxis(QAbstractAxis *axis)
+{
+    Q_ASSERT(axis);
+    Abstract3DController *owner = qobject_cast<Abstract3DController *>(axis->parent());
+    if (owner != this) {
+        Q_ASSERT_X(!owner, "addAxis", "Axis already attached to a graph.");
+        axis->setParent(this);
+    }
+    if (!m_axes.contains(axis))
+        m_axes.append(axis);
+}
+
+void Abstract3DController::releaseAxis(QAbstractAxis *axis)
+{
+    if (axis && m_axes.contains(axis)) {
+        // If the axis is in use, replace it with a temporary one
+        switch (axis->orientation()) {
+        case QAbstractAxis::AxisOrientationX:
+            setAxisX(0);
+            break;
+        case QAbstractAxis::AxisOrientationY:
+            setAxisY(0);
+            break;
+        case QAbstractAxis::AxisOrientationZ:
+            setAxisZ(0);
+            break;
+        default:
+            break;
+        }
+
+        m_axes.removeAll(axis);
+        axis->setParent(0);
+    }
+}
+
+QList<QAbstractAxis *> Abstract3DController::axes() const
+{
+    QList<QAbstractAxis *> retList;
+    foreach (QAbstractAxis *axis, m_axes) {
+        if (!axis->d_ptr->isDefaultAxis())
+            retList.append(axis);
+    }
+
+    return retList;
+}
+
 int Abstract3DController::zoomLevel()
 {
     return m_zoomLevel;
@@ -658,25 +710,48 @@ void Abstract3DController::handleAxisLabelFormatChanged(const QString &format)
 
 void Abstract3DController::handleAxisLabelFormatChangedBySender(QObject *sender)
 {
-    if (sender == m_axisX)
+    // Label format changing needs to dirty the data so that labels are reset.
+    if (sender == m_axisX) {
+        m_isDataDirty = true;
         m_changeTracker.axisXLabelFormatChanged = true;
-    else if (sender == m_axisY)
+    } else if (sender == m_axisY) {
+        m_isDataDirty = true;
         m_changeTracker.axisYLabelFormatChanged = true;
-    else if (sender == m_axisZ)
+    } else if (sender == m_axisZ) {
+        m_isDataDirty = true;
         m_changeTracker.axisZLabelFormatChanged = true;
-    else
+    } else {
         qWarning() << __FUNCTION__ << "invoked for invalid axis";
+    }
 }
 
 void Abstract3DController::setAxisHelper(QAbstractAxis::AxisOrientation orientation,
                                          QAbstractAxis *axis, QAbstractAxis **axisPtr)
 {
-    Q_ASSERT(axis);
+    // Setting null axis indicates using default axis
+    if (axis == 0)
+        axis = createDefaultAxis(orientation);
+
+    // If old axis is default axis, delete it
+    QAbstractAxis *oldAxis = *axisPtr;
+    if (oldAxis) {
+        if (oldAxis->d_ptr->isDefaultAxis()) {
+            m_axes.removeAll(oldAxis);
+            delete oldAxis;
+            oldAxis = 0;
+        } else {
+            // Disconnect the old axis from use
+            QObject::disconnect(oldAxis, 0, this, 0);
+            oldAxis->d_ptr->setOrientation(QAbstractAxis::AxisOrientationNone);
+        }
+    }
 
-    delete *axisPtr;
+    // Assume ownership
+    addAxis(axis);
+
+    // Connect the new axis
     *axisPtr = axis;
 
-    axis->setParent(0); // Assume ownership
     axis->d_ptr->setOrientation(orientation);
 
     QObject::connect(axis, &QAbstractAxis::titleChanged,
@@ -716,4 +791,37 @@ void Abstract3DController::setAxisHelper(QAbstractAxis::AxisOrientation orientat
     }
 }
 
+QAbstractAxis *Abstract3DController::createDefaultAxis(QAbstractAxis::AxisOrientation orientation)
+{
+    Q_UNUSED(orientation)
+
+    // The default default axis is a value axis. If the chart type has a different default axis
+    // for some orientation, this function needs to be overridden.
+    QAbstractAxis *defaultAxis = createDefaultValueAxis();
+    return defaultAxis;
+}
+
+QValueAxis *Abstract3DController::createDefaultValueAxis()
+{
+    // Default value axis has single segment, empty label format, and auto scaling
+    // TODO: Grid should be also hidden, but that is not currently controlled by axis
+    QValueAxis *defaultAxis = new QValueAxis;
+    defaultAxis->setSegmentCount(1);
+    defaultAxis->setSubSegmentCount(1);
+    defaultAxis->setAutoAdjustRange(true);
+    defaultAxis->setLabelFormat(QString());
+    defaultAxis->d_ptr->setDefaultAxis(true);
+
+    return defaultAxis;
+}
+
+QCategoryAxis *Abstract3DController::createDefaultCategoryAxis()
+{
+    // Default category axis has no labels
+    // TODO: Grid should be also hidden, but that is not currently controlled by axis.
+    QCategoryAxis *defaultAxis = new QCategoryAxis;
+    defaultAxis->d_ptr->setDefaultAxis(true);
+    return defaultAxis;
+}
+
 QT_DATAVIS3D_END_NAMESPACE
diff --git a/src/datavis3d/engine/abstract3dcontroller_p.h b/src/datavis3d/engine/abstract3dcontroller_p.h
index 4868e3eb..3123a5d7 100644
--- a/src/datavis3d/engine/abstract3dcontroller_p.h
+++ b/src/datavis3d/engine/abstract3dcontroller_p.h
@@ -156,9 +156,12 @@ protected:
     QAbstract3DInputHandler *m_inputHandler;
     CameraHelper *m_cameraHelper;
     int m_zoomLevel;
+    // Active axes
     QAbstractAxis *m_axisX;
     QAbstractAxis *m_axisY;
     QAbstractAxis *m_axisZ;
+
+    QList<QAbstractAxis *> m_axes; // List of all added axes
     Abstract3DRenderer *m_renderer;
     bool m_isDataDirty;
 
@@ -201,6 +204,9 @@ public:
     virtual QAbstractAxis *axisY();
     virtual void setAxisZ(QAbstractAxis *axis);
     virtual QAbstractAxis *axisZ();
+    virtual void addAxis(QAbstractAxis *axis);
+    virtual void releaseAxis(QAbstractAxis *axis);
+    virtual QList<QAbstractAxis *> axes() const; // Omits default axes
 
     virtual int zoomLevel();
     virtual void setZoomLevel(int zoomLevel);
@@ -283,6 +289,11 @@ signals:
     void gridEnabledChanged(bool enable); // TODO: Should be handled via axes?
     void meshFileNameChanged(QString fileName);
 
+protected:
+    virtual QAbstractAxis *createDefaultAxis(QAbstractAxis::AxisOrientation orientation);
+    QValueAxis *createDefaultValueAxis();
+    QCategoryAxis *createDefaultCategoryAxis();
+
 private:
     void setAxisHelper(QAbstractAxis::AxisOrientation orientation, QAbstractAxis *axis,
                        QAbstractAxis **axisPtr);
diff --git a/src/datavis3d/engine/abstract3drenderer.cpp b/src/datavis3d/engine/abstract3drenderer.cpp
index 2b40955c..a1800ba8 100644
--- a/src/datavis3d/engine/abstract3drenderer.cpp
+++ b/src/datavis3d/engine/abstract3drenderer.cpp
@@ -111,8 +111,6 @@ void Abstract3DRenderer::render(CameraHelper *camera, const GLuint defaultFboHan
 QString Abstract3DRenderer::generateValueLabel(const QString &format, qreal value)
 {
     QString valueLabelFormat = format;
-    if (valueLabelFormat.isEmpty())
-        valueLabelFormat = Utils::defaultLabelFormat();
     Utils::ParamType valueParamType = Utils::findFormatParamType(valueLabelFormat);
     QByteArray valueFormatArray = valueLabelFormat.toUtf8();
     return Utils::formatLabel(valueFormatArray, valueParamType, value);
diff --git a/src/datavis3d/engine/axisrendercache.cpp b/src/datavis3d/engine/axisrendercache.cpp
index 4374d545..0ca92247 100644
--- a/src/datavis3d/engine/axisrendercache.cpp
+++ b/src/datavis3d/engine/axisrendercache.cpp
@@ -52,11 +52,21 @@ void AxisRenderCache::setType(QAbstractAxis::AxisType type)
 {
     m_type = type;
 
-    // If type is set, it means completely new axis instance, so clear all generated label items.
+    // If type is set, it means completely new axis instance, so clear all old data
+    m_labels.clear();
+    m_title.clear();
+    m_min = 0.0;
+    m_max = 10.0;
+    m_segmentCount = 5;
+    m_subSegmentCount = 1;
+    m_labelFormat.clear();
+
     m_titleItem.clear();
     foreach (LabelItem *label, m_labelItems)
         delete label;
     m_labelItems.clear();
+    m_segmentStep = 10.0f;
+    m_subSegmentStep = 10.0f;
 }
 
 void AxisRenderCache::setTitle(const QString &title)
@@ -80,10 +90,10 @@ void AxisRenderCache::setLabels(const QStringList &labels)
 
         m_labelItems.reserve(newSize);
 
-        if (m_drawer) {
-            for (int i = 0; i < newSize; i++) {
-                if (i >= oldSize)
-                    m_labelItems.append(new LabelItem);
+        for (int i = 0; i < newSize; i++) {
+            if (i >= oldSize)
+                m_labelItems.append(new LabelItem);
+            if (m_drawer) {
                 if (labels.at(i).isEmpty())
                     m_labelItems[i]->clear();
                 else if (i >= oldSize || labels.at(i) != m_labels.at(i))
diff --git a/src/datavis3d/engine/bars3dcontroller.cpp b/src/datavis3d/engine/bars3dcontroller.cpp
index 13dce382..36a00319 100644
--- a/src/datavis3d/engine/bars3dcontroller.cpp
+++ b/src/datavis3d/engine/bars3dcontroller.cpp
@@ -44,15 +44,17 @@ Bars3dController::Bars3dController(QRect boundRect)
       m_renderer(0),
       m_data(0)
 {
-    // Default axes
-    setAxisX(new QCategoryAxis());
-    setAxisY(new QValueAxis());
-    setAxisZ(new QCategoryAxis());
-
     // Default bar type; specific to bars
     setBarType(QDataVis::Bars, false);
 
     setDataProxy(new QBarDataProxy);
+
+    // Setting a null axis creates a new default axis according to orientation and chart type.
+    // Note: These cannot be set in Abstract3DController constructor, as they will call virtual
+    //       functions implemented by subclasses.
+    setAxisX(0);
+    setAxisY(0);
+    setAxisZ(0);
 }
 
 Bars3dController::~Bars3dController()
@@ -502,4 +504,16 @@ void Bars3dController::adjustValueAxisRange()
     }
 }
 
+QAbstractAxis *Bars3dController::createDefaultAxis(QAbstractAxis::AxisOrientation orientation)
+{
+    QAbstractAxis *defaultAxis = 0;
+
+    if (orientation == QAbstractAxis::AxisOrientationY)
+        defaultAxis = createDefaultValueAxis();
+    else
+        defaultAxis = createDefaultCategoryAxis();
+
+    return defaultAxis;
+}
+
 QT_DATAVIS3D_END_NAMESPACE
diff --git a/src/datavis3d/engine/bars3dcontroller_p.h b/src/datavis3d/engine/bars3dcontroller_p.h
index f7016860..bdff63b3 100644
--- a/src/datavis3d/engine/bars3dcontroller_p.h
+++ b/src/datavis3d/engine/bars3dcontroller_p.h
@@ -152,6 +152,9 @@ signals:
     void barSpecsChanged(GLfloat thicknessRatio, QSizeF spacing, bool relative);
     void selectedBarPosChanged(QPoint position);
 
+protected:
+    virtual QAbstractAxis *createDefaultAxis(QAbstractAxis::AxisOrientation orientation);
+
 private:
     void adjustValueAxisRange();
 
diff --git a/src/datavis3d/engine/bars3drenderer.cpp b/src/datavis3d/engine/bars3drenderer.cpp
index ce05b0b9..ce7dd0e4 100644
--- a/src/datavis3d/engine/bars3drenderer.cpp
+++ b/src/datavis3d/engine/bars3drenderer.cpp
@@ -1360,7 +1360,10 @@ void Bars3dRenderer::drawScene(CameraHelper *camera,
                 labelText.replace(valueTitleTag, m_axisCacheY.title());
 
                 if (labelText.contains(valueLabelTag)) {
-                    QString valueLabelText = generateValueLabel(m_axisCacheY.labelFormat(), selectedBar->value());
+                    QString labelFormat = m_axisCacheY.labelFormat();
+                    if (labelFormat.isEmpty())
+                        labelFormat = Utils::defaultLabelFormat();
+                    QString valueLabelText = generateValueLabel(labelFormat, selectedBar->value());
                     labelText.replace(valueLabelTag, valueLabelText);
                 }
 
diff --git a/src/datavis3d/engine/drawer.cpp b/src/datavis3d/engine/drawer.cpp
index d2e3ddaf..9ea958ba 100644
--- a/src/datavis3d/engine/drawer.cpp
+++ b/src/datavis3d/engine/drawer.cpp
@@ -321,18 +321,20 @@ void Drawer::generateLabelItem(LabelItem &item, const QString &text)
 
     item.clear();
 
-    // Create labels
-    // Print label into a QImage using QPainter
-    QImage label = Utils::printTextToImage(m_font,
-                                           text,
-                                           m_theme.m_textBackgroundColor,
-                                           m_theme.m_textColor,
-                                           m_transparency);
-
-    // Set label size
-    item.setSize(label.size());
-    // Insert text texture into label (also deletes the old texture)
-    item.setTextureId(m_textureHelper->create2DTexture(label, true, true));
+    if (!text.isEmpty()) {
+        // Create labels
+        // Print label into a QImage using QPainter
+        QImage label = Utils::printTextToImage(m_font,
+                                               text,
+                                               m_theme.m_textBackgroundColor,
+                                               m_theme.m_textColor,
+                                               m_transparency);
+
+        // Set label size
+        item.setSize(label.size());
+        // Insert text texture into label (also deletes the old texture)
+        item.setTextureId(m_textureHelper->create2DTexture(label, true, true));
+    }
 }
 
 QT_DATAVIS3D_END_NAMESPACE
diff --git a/src/datavis3d/engine/q3dbars.cpp b/src/datavis3d/engine/q3dbars.cpp
index cf196ac8..5c2cf0c8 100644
--- a/src/datavis3d/engine/q3dbars.cpp
+++ b/src/datavis3d/engine/q3dbars.cpp
@@ -20,6 +20,7 @@
 #include "q3dbars_p.h"
 #include "bars3dcontroller_p.h"
 #include "qvalueaxis.h"
+#include "qcategoryaxis.h"
 
 #include <QMouseEvent>
 
@@ -394,7 +395,7 @@ QPoint Q3DBars::selectedBarPos() const
  */
 void Q3DBars::setShadowQuality(QDataVis::ShadowQuality quality)
 {
-    return d_ptr->m_shared->setShadowQuality(quality);
+    d_ptr->m_shared->setShadowQuality(quality);
 }
 
 QDataVis::ShadowQuality Q3DBars::shadowQuality() const
@@ -403,33 +404,65 @@ QDataVis::ShadowQuality Q3DBars::shadowQuality() const
 }
 
 /*!
- * \return category axis for rows.
+ * Sets a user-defined row \a axis. Implicitly calls addAxis() to transfer ownership of
+ * the \a axis to this graph.
+ *
+ * If the \a axis is null, or if user doesn't explicitly set row axis at all, a temporary
+ * default axis with no labels is used.
+ *
+ * \sa addAxis(), releaseAxis()
+ */
+void Q3DBars::setRowAxis(QCategoryAxis *axis)
+{
+    d_ptr->m_shared->setAxisX(axis);
+}
+
+/*!
+ * \return category axis for rows. Returns null pointer if default axis is in use.
  */
 QCategoryAxis *Q3DBars::rowAxis() const
 {
-    return reinterpret_cast<QCategoryAxis *>(d_ptr->m_shared->axisX());
+    return static_cast<QCategoryAxis *>(d_ptr->m_shared->axisX());
+}
+
+/*!
+ * Sets a user-defined column \a axis. Implicitly calls addAxis() to transfer ownership of
+ * the \a axis to this graph.
+ *
+ * If the \a axis is null, or if user doesn't explicitly set column axis at all, a temporary
+ * default axis with no labels is used.
+ *
+ * \sa addAxis(), releaseAxis()
+ */
+void Q3DBars::setColumnAxis(QCategoryAxis *axis)
+{
+    d_ptr->m_shared->setAxisZ(axis);
 }
 
 /*!
- * \return category axis for columns.
+ * \return category axis for columns. Returns null pointer if default axis is in use.
  */
 QCategoryAxis *Q3DBars::columnAxis() const
 {
-    return reinterpret_cast<QCategoryAxis *>(d_ptr->m_shared->axisZ());
+    return static_cast<QCategoryAxis *>(d_ptr->m_shared->axisZ());
 }
 
 /*!
- * Sets a user-defined value \a axis (Y-axis). Ownership of the axis is transferred to Q3DBars.
+ * Sets a user-defined value \a axis (the Y-axis). Implicitly calls addAxis() to transfer ownership
+ * of the \a axis to this graph.
+ *
+ * If the \a axis is null, or if user doesn't explicitly set value axis at all, a temporary
+ * default axis with no labels and automatic range adjusting is used.
+ *
+ * \sa addAxis(), releaseAxis()
  */
 void Q3DBars::setValueAxis(QValueAxis *axis)
 {
-    Q_ASSERT(axis);
-
-    return d_ptr->m_shared->setAxisY(axis);
+    d_ptr->m_shared->setAxisY(axis);
 }
 
 /*!
- * \return used value axis (Y-axis).
+ * \return used value axis (Y-axis). Returns null pointer if default axis is in use.
  */
 QValueAxis *Q3DBars::valueAxis() const
 {
@@ -437,6 +470,39 @@ QValueAxis *Q3DBars::valueAxis() const
 }
 
 /*!
+ * Adds \a axis to the graph. The axes added via addAxis are not yet taken to use,
+ * addAxis is simply used to give the ownership of the \a axis to the graph.
+ * The \a axis must not be null or added to another graph.
+ *
+ * \sa releaseAxis(), setValueAxis(), setRowAxis(), setColumnAxis()
+ */
+void Q3DBars::addAxis(QAbstractAxis *axis)
+{
+    d_ptr->m_shared->addAxis(axis);
+}
+
+/*!
+ * Releases the ownership of the \a axis back to the caller, if it is added to this graph.
+ * If the released \a axis is in use, a temporary default axis will be set active.
+ *
+ * \sa addAxis(), setValueAxis(), setRowAxis(), setColumnAxis()
+ */
+void Q3DBars::releaseAxis(QAbstractAxis *axis)
+{
+    d_ptr->m_shared->releaseAxis(axis);
+}
+
+/*!
+ * \return list of all added axes.
+ *
+ * \sa addAxis()
+ */
+QList<QAbstractAxis *> Q3DBars::axes() const
+{
+    return d_ptr->m_shared->axes();
+}
+
+/*!
  * Sets a user-defined data \a proxy. Ownership of the proxy is transferred to Q3DBars.
  */
 void Q3DBars::setDataProxy(QBarDataProxy *proxy)
diff --git a/src/datavis3d/engine/q3dbars.h b/src/datavis3d/engine/q3dbars.h
index ff6a6fad..b3e695d3 100644
--- a/src/datavis3d/engine/q3dbars.h
+++ b/src/datavis3d/engine/q3dbars.h
@@ -26,6 +26,7 @@
 QT_DATAVIS3D_BEGIN_NAMESPACE
 
 class Q3DBarsPrivate;
+class QAbstractAxis;
 class QCategoryAxis;
 class QValueAxis;
 class QBarDataProxy;
@@ -93,10 +94,15 @@ public:
     void setShadowQuality(QDataVis::ShadowQuality quality);
     QDataVis::ShadowQuality shadowQuality() const;
 
+    void setRowAxis(QCategoryAxis *axis);
     QCategoryAxis *rowAxis() const;
+    void setColumnAxis(QCategoryAxis *axis);
     QCategoryAxis *columnAxis() const;
     void setValueAxis(QValueAxis *axis);
     QValueAxis *valueAxis() const;
+    void addAxis(QAbstractAxis *axis);
+    void releaseAxis(QAbstractAxis *axis);
+    QList<QAbstractAxis *> axes() const;
 
     void setDataProxy(QBarDataProxy *proxy);
     QBarDataProxy *dataProxy();
diff --git a/src/datavis3d/engine/q3dscatter.cpp b/src/datavis3d/engine/q3dscatter.cpp
index 7fc6f628..bd9a884f 100644
--- a/src/datavis3d/engine/q3dscatter.cpp
+++ b/src/datavis3d/engine/q3dscatter.cpp
@@ -365,60 +365,109 @@ QDataVis::ShadowQuality Q3DScatter::shadowQuality() const
 }
 
 /*!
- * Sets a user-defined value \a axis (X-axis). Ownership of the axis is transferred to Q3DScatter.
+ * Sets a user-defined X-axis. Implicitly calls addAxis() to transfer ownership
+ * of the \a axis to this graph.
+ *
+ * If the \a axis is null, or if user doesn't explicitly set value axis at all, a temporary
+ * default axis with no labels and automatic range adjusting is used.
+ *
+ * \sa addAxis(), releaseAxis()
  */
-void Q3DScatter::setValueAxisX(QValueAxis *axis)
+void Q3DScatter::setAxisX(QValueAxis *axis)
 {
-    Q_ASSERT(axis);
-
-    return d_ptr->m_shared->setAxisX(axis);
+    d_ptr->m_shared->setAxisX(axis);
 }
 
 /*!
- * \return used value axis (X-axis).
+ * \return used X-axis. Returns null pointer if default axis is in use.
  */
-QValueAxis *Q3DScatter::valueAxisX() const
+QValueAxis *Q3DScatter::axisX() const
 {
     return static_cast<QValueAxis *>(d_ptr->m_shared->axisX());
 }
 
 /*!
- * Sets a user-defined value \a axis (Y-axis). Ownership of the axis is transferred to Q3DScatter.
+ * Sets a user-defined Y-axis. Implicitly calls addAxis() to transfer ownership
+ * of the \a axis to this graph.
+ *
+ * If the \a axis is null, or if user doesn't explicitly set value axis at all, a temporary
+ * default axis with no labels and automatic range adjusting is used.
+ *
+ * \sa addAxis(), releaseAxis()
  */
-void Q3DScatter::setValueAxisY(QValueAxis *axis)
+void Q3DScatter::setAxisY(QValueAxis *axis)
 {
-    Q_ASSERT(axis);
-
-    return d_ptr->m_shared->setAxisY(axis);
+    d_ptr->m_shared->setAxisY(axis);
 }
 
 /*!
- * \return used value axis (Y-axis).
+ * \return used Y-axis. Returns null pointer if default axis is in use.
  */
-QValueAxis *Q3DScatter::valueAxisY() const
+QValueAxis *Q3DScatter::axisY() const
 {
     return static_cast<QValueAxis *>(d_ptr->m_shared->axisY());
 }
 
 /*!
- * Sets a user-defined value \a axis (Z-axis). Ownership of the axis is transferred to Q3DScatter.
+ * Sets a user-defined Z-axis. Implicitly calls addAxis() to transfer ownership
+ * of the \a axis to this graph.
+ *
+ * If the \a axis is null, or if user doesn't explicitly set value axis at all, a temporary
+ * default axis with no labels and automatic range adjusting is used.
+ *
+ * \sa addAxis(), releaseAxis()
  */
-void Q3DScatter::setValueAxisZ(QValueAxis *axis)
+void Q3DScatter::setAxisZ(QValueAxis *axis)
 {
-    Q_ASSERT(axis);
-
-    return d_ptr->m_shared->setAxisZ(axis);
+    d_ptr->m_shared->setAxisZ(axis);
 }
 
 /*!
- * \return used value axis (Z-axis).
+ * \return used Z-axis. Returns null pointer if default axis is in use.
  */
-QValueAxis *Q3DScatter::valueAxisZ() const
+QValueAxis *Q3DScatter::axisZ() const
 {
     return static_cast<QValueAxis *>(d_ptr->m_shared->axisZ());
 }
 
 /*!
+ * Adds \a axis to the graph. The axes added via addAxis are not yet taken to use,
+ * addAxis is simply used to give the ownership of the \a axis to the graph.
+ * The \a axis must not be null or added to another graph.
+ *
+ * \sa releaseAxis(), setAxisX(), setAxisY(), setAxisZ()
+ */
+void Q3DScatter::addAxis(QValueAxis *axis)
+{
+    d_ptr->m_shared->addAxis(axis);
+}
+
+/*!
+ * Releases the ownership of the \a axis back to the caller, if it is added to this graph.
+ *
+ * \sa addAxis(), setAxisX(), setAxisY(), setAxisZ()
+ */
+void Q3DScatter::releaseAxis(QValueAxis *axis)
+{
+    d_ptr->m_shared->releaseAxis(axis);
+}
+
+/*!
+ * \return list of all added axes.
+ *
+ * \sa addAxis()
+ */
+QList<QValueAxis *> Q3DScatter::axes() const
+{
+    QList<QAbstractAxis *> abstractAxes = d_ptr->m_shared->axes();
+    QList<QValueAxis *> retList;
+    foreach (QAbstractAxis *axis, abstractAxes)
+        retList.append(static_cast<QValueAxis *>(axis));
+
+    return retList;
+}
+
+/*!
  * Sets a user-defined data \a proxy. Ownership of the proxy is transferred to Q3DScatter.
  */
 void Q3DScatter::setDataProxy(QScatterDataProxy *proxy)
diff --git a/src/datavis3d/engine/q3dscatter.h b/src/datavis3d/engine/q3dscatter.h
index 26e3da08..a432b101 100644
--- a/src/datavis3d/engine/q3dscatter.h
+++ b/src/datavis3d/engine/q3dscatter.h
@@ -86,14 +86,15 @@ public:
     void setShadowQuality(QDataVis::ShadowQuality quality);
     QDataVis::ShadowQuality shadowQuality() const;
 
-    void setValueAxisX(QValueAxis *axis);
-    QValueAxis *valueAxisX() const;
-
-    void setValueAxisY(QValueAxis *axis);
-    QValueAxis *valueAxisY() const;
-
-    void setValueAxisZ(QValueAxis *axis);
-    QValueAxis *valueAxisZ() const;
+    void setAxisX(QValueAxis *axis);
+    QValueAxis *axisX() const;
+    void setAxisY(QValueAxis *axis);
+    QValueAxis *axisY() const;
+    void setAxisZ(QValueAxis *axis);
+    QValueAxis *axisZ() const;
+    void addAxis(QValueAxis *axis);
+    void releaseAxis(QValueAxis *axis);
+    QList<QValueAxis *> axes() const;
 
     void setDataProxy(QScatterDataProxy *proxy);
     QScatterDataProxy *dataProxy();
diff --git a/src/datavis3d/engine/q3dsurface.cpp b/src/datavis3d/engine/q3dsurface.cpp
index d4b5f2f1..2201053d 100644
--- a/src/datavis3d/engine/q3dsurface.cpp
+++ b/src/datavis3d/engine/q3dsurface.cpp
@@ -154,42 +154,109 @@ void Q3DSurface::setSegmentCount(int segmentCount, qreal step, qreal minimum)
     d_ptr->m_shared->setSegmentCount(GLint(segmentCount), GLfloat(step), GLfloat(minimum));
 }
 
-void Q3DSurface::setValueAxisX(QValueAxis *axis)
+/*!
+ * Sets a user-defined X-axis. Implicitly calls addAxis() to transfer ownership
+ * of the \a axis to this graph.
+ *
+ * If the \a axis is null, or if user doesn't explicitly set value axis at all, a temporary
+ * default axis with no labels and automatic range adjusting is used.
+ *
+ * \sa addAxis(), releaseAxis()
+ */
+void Q3DSurface::setAxisX(QValueAxis *axis)
 {
-    Q_ASSERT(axis);
-
-    return d_ptr->m_shared->setAxisX(axis);
+    d_ptr->m_shared->setAxisX(axis);
 }
 
-QValueAxis *Q3DSurface::valueAxisX()
+/*!
+ * \return used X-axis. Returns null pointer if default axis is in use.
+ */
+QValueAxis *Q3DSurface::axisX() const
 {
     return static_cast<QValueAxis *>(d_ptr->m_shared->axisX());
 }
 
-void Q3DSurface::setValueAxisY(QValueAxis *axis)
+/*!
+ * Sets a user-defined Y-axis. Implicitly calls addAxis() to transfer ownership
+ * of the \a axis to this graph.
+ *
+ * If the \a axis is null, or if user doesn't explicitly set value axis at all, a temporary
+ * default axis with no labels and automatic range adjusting is used.
+ *
+ * \sa addAxis(), releaseAxis()
+ */
+void Q3DSurface::setAxisY(QValueAxis *axis)
 {
-    Q_ASSERT(axis);
-
-    return d_ptr->m_shared->setAxisY(axis);
+    d_ptr->m_shared->setAxisY(axis);
 }
 
-QValueAxis *Q3DSurface::valueAxisY()
+/*!
+ * \return used Y-axis. Returns null pointer if default axis is in use.
+ */
+QValueAxis *Q3DSurface::axisY() const
 {
     return static_cast<QValueAxis *>(d_ptr->m_shared->axisY());
 }
 
-void Q3DSurface::setValueAxisZ(QValueAxis *axis)
+/*!
+ * Sets a user-defined Z-axis. Implicitly calls addAxis() to transfer ownership
+ * of the \a axis to this graph.
+ *
+ * If the \a axis is null, or if user doesn't explicitly set value axis at all, a temporary
+ * default axis with no labels and automatic range adjusting is used.
+ *
+ * \sa addAxis(), releaseAxis()
+ */
+void Q3DSurface::setAxisZ(QValueAxis *axis)
 {
-    Q_ASSERT(axis);
-
-    return d_ptr->m_shared->setAxisZ(axis);
+    d_ptr->m_shared->setAxisZ(axis);
 }
 
-QValueAxis *Q3DSurface::valueAxisZ()
+/*!
+ * \return used Z-axis. Returns null pointer if default axis is in use.
+ */
+QValueAxis *Q3DSurface::axisZ() const
 {
     return static_cast<QValueAxis *>(d_ptr->m_shared->axisZ());
 }
 
+/*!
+ * Adds \a axis to the graph. The axes added via addAxis are not yet taken to use,
+ * addAxis is simply used to give the ownership of the \a axis to the graph.
+ * The \a axis must not be null or added to another graph.
+ *
+ * \sa releaseAxis(), setAxisX(), setAxisY(), setAxisZ()
+ */
+void Q3DSurface::addAxis(QValueAxis *axis)
+{
+    d_ptr->m_shared->addAxis(axis);
+}
+
+/*!
+ * Releases the ownership of the \a axis back to the caller, if it is added to this graph.
+ *
+ * \sa addAxis(), setAxisX(), setAxisY(), setAxisZ()
+ */
+void Q3DSurface::releaseAxis(QValueAxis *axis)
+{
+    d_ptr->m_shared->releaseAxis(axis);
+}
+
+/*!
+ * \return list of all added axes.
+ *
+ * \sa addAxis()
+ */
+QList<QValueAxis *> Q3DSurface::axes() const
+{
+    QList<QAbstractAxis *> abstractAxes = d_ptr->m_shared->axes();
+    QList<QValueAxis *> retList;
+    foreach (QAbstractAxis *axis, abstractAxes)
+        retList.append(static_cast<QValueAxis *>(axis));
+
+    return retList;
+}
+
 void Q3DSurface::setGradientColorAt(qreal pos, const QColor &color)
 {
     d_ptr->m_shared->setGradientColorAt(pos, color);
diff --git a/src/datavis3d/engine/q3dsurface.h b/src/datavis3d/engine/q3dsurface.h
index 357d65bd..c46a3710 100644
--- a/src/datavis3d/engine/q3dsurface.h
+++ b/src/datavis3d/engine/q3dsurface.h
@@ -58,14 +58,15 @@ public:
     void setGradientColorAt(qreal pos, const QColor &color);
 
     // Axes
-    void setValueAxisX(QValueAxis *axis);
-    QValueAxis *valueAxisX();
-
-    void setValueAxisY(QValueAxis *axis);
-    QValueAxis *valueAxisY();
-
-    void setValueAxisZ(QValueAxis *axis);
-    QValueAxis *valueAxisZ();
+    void setAxisX(QValueAxis *axis);
+    QValueAxis *axisX() const;
+    void setAxisY(QValueAxis *axis);
+    QValueAxis *axisY() const;
+    void setAxisZ(QValueAxis *axis);
+    QValueAxis *axisZ() const;
+    void addAxis(QValueAxis *axis);
+    void releaseAxis(QValueAxis *axis);
+    QList<QValueAxis *> axes() const;
 
     // TODO: Remove when axes handling in use
     void setSegmentCount(int segmentCount, qreal step, qreal minimum = 0.0f);
diff --git a/src/datavis3d/engine/scatter3dcontroller.cpp b/src/datavis3d/engine/scatter3dcontroller.cpp
index 3b0a2c1f..c5ed1fed 100644
--- a/src/datavis3d/engine/scatter3dcontroller.cpp
+++ b/src/datavis3d/engine/scatter3dcontroller.cpp
@@ -38,15 +38,17 @@ Scatter3DController::Scatter3DController(QRect boundRect)
       m_data(0),
       m_selectedItemIndex(noSelectionIndex())
 {
-    // Default axes
-    setAxisX(new QValueAxis());
-    setAxisY(new QValueAxis());
-    setAxisZ(new QValueAxis());
-
     // Default object type; specific to scatter
     setObjectType(QDataVis::Spheres, false);
 
     setDataProxy(new QScatterDataProxy);
+
+    // Setting a null axis creates a new default axis according to orientation and chart type.
+    // Note: These cannot be set in Abstract3DController constructor, as they will call virtual
+    //       functions implemented by subclasses.
+    setAxisX(0);
+    setAxisY(0);
+    setAxisZ(0);
 }
 
 Scatter3DController::~Scatter3DController()
diff --git a/src/datavis3d/engine/scatter3drenderer.cpp b/src/datavis3d/engine/scatter3drenderer.cpp
index 600726f1..bee1ee5c 100644
--- a/src/datavis3d/engine/scatter3drenderer.cpp
+++ b/src/datavis3d/engine/scatter3drenderer.cpp
@@ -1324,17 +1324,26 @@ void Scatter3DRenderer::drawScene(CameraHelper *camera,
                 labelText.replace(zTitleTag, m_axisCacheZ.title());
 
                 if (labelText.contains(xLabelTag)) {
-                    QString valueLabelText = generateValueLabel(m_axisCacheX.labelFormat(),
+                    QString labelFormat = m_axisCacheX.labelFormat();
+                    if (labelFormat.isEmpty())
+                        labelFormat = Utils::defaultLabelFormat();
+                    QString valueLabelText = generateValueLabel(labelFormat,
                                                                 selectedItem->position().x());
                     labelText.replace(xLabelTag, valueLabelText);
                 }
                 if (labelText.contains(yLabelTag)) {
-                    QString valueLabelText = generateValueLabel(m_axisCacheY.labelFormat(),
+                    QString labelFormat = m_axisCacheY.labelFormat();
+                    if (labelFormat.isEmpty())
+                        labelFormat = Utils::defaultLabelFormat();
+                    QString valueLabelText = generateValueLabel(labelFormat,
                                                                 selectedItem->position().y());
                     labelText.replace(yLabelTag, valueLabelText);
                 }
                 if (labelText.contains(zLabelTag)) {
-                    QString valueLabelText = generateValueLabel(m_axisCacheZ.labelFormat(),
+                    QString labelFormat = m_axisCacheZ.labelFormat();
+                    if (labelFormat.isEmpty())
+                        labelFormat = Utils::defaultLabelFormat();
+                    QString valueLabelText = generateValueLabel(labelFormat,
                                                                 selectedItem->position().z());
                     labelText.replace(zLabelTag, valueLabelText);
                 }
diff --git a/src/datavis3d/engine/surface3dcontroller.cpp b/src/datavis3d/engine/surface3dcontroller.cpp
index 89ec4fe6..dd21f388 100644
--- a/src/datavis3d/engine/surface3dcontroller.cpp
+++ b/src/datavis3d/engine/surface3dcontroller.cpp
@@ -38,10 +38,12 @@ Surface3dController::Surface3dController(QRect rect)
       m_mouseState(MouseNone),
       m_mousePos(QPoint(0, 0))
 {
-    // Default axes
-    setAxisX(new QValueAxis()); // Or QCategoryAxis
-    setAxisY(new QValueAxis());
-    setAxisZ(new QValueAxis()); // Or QCategoryAxis
+    // Setting a null axis creates a new default axis according to orientation and chart type.
+    // Note: These cannot be set in Abstract3DController constructor, as they will call virtual
+    //       functions implemented by subclasses.
+    setAxisX(0);
+    setAxisY(0);
+    setAxisZ(0);
 }
 
 Surface3dController::~Surface3dController()
diff --git a/src/datavis3dqml2/declarativebars.cpp b/src/datavis3dqml2/declarativebars.cpp
index 6c63bda4..32ed5c57 100644
--- a/src/datavis3dqml2/declarativebars.cpp
+++ b/src/datavis3dqml2/declarativebars.cpp
@@ -125,32 +125,32 @@ void DeclarativeBars::setMapping(QItemModelBarDataMapping *mapping)
     static_cast<QItemModelBarDataProxy *>(m_shared->dataProxy())->setMapping(mapping);
 }
 
-QCategoryAxis *DeclarativeBars::axisX() const
+QCategoryAxis *DeclarativeBars::rowAxis() const
 {
     return static_cast<QCategoryAxis *>(m_shared->axisX());
 }
 
-void DeclarativeBars::setAxisX(QCategoryAxis *axis)
+void DeclarativeBars::setRowAxis(QCategoryAxis *axis)
 {
     m_shared->setAxisX(axis);
 }
 
-QValueAxis *DeclarativeBars::axisY() const
+QValueAxis *DeclarativeBars::valueAxis() const
 {
     return static_cast<QValueAxis *>(m_shared->axisY());
 }
 
-void DeclarativeBars::setAxisY(QValueAxis *axis)
+void DeclarativeBars::setValueAxis(QValueAxis *axis)
 {
     m_shared->setAxisY(axis);
 }
 
-QCategoryAxis *DeclarativeBars::axisZ() const
+QCategoryAxis *DeclarativeBars::columnAxis() const
 {
     return static_cast<QCategoryAxis *>(m_shared->axisZ());
 }
 
-void DeclarativeBars::setAxisZ(QCategoryAxis *axis)
+void DeclarativeBars::setColumnAxis(QCategoryAxis *axis)
 {
     m_shared->setAxisZ(axis);
 }
diff --git a/src/datavis3dqml2/declarativebars_p.h b/src/datavis3dqml2/declarativebars_p.h
index 5a8fb165..6ada9a35 100644
--- a/src/datavis3dqml2/declarativebars_p.h
+++ b/src/datavis3dqml2/declarativebars_p.h
@@ -48,9 +48,9 @@ class DeclarativeBars : public QQuickItem
     Q_OBJECT
     Q_PROPERTY(QAbstractItemModel *data READ data WRITE setData)
     Q_PROPERTY(QItemModelBarDataMapping *mapping READ mapping WRITE setMapping)
-    Q_PROPERTY(QCategoryAxis *axisX READ axisX WRITE setAxisX)
-    Q_PROPERTY(QValueAxis *axisY READ axisY WRITE setAxisY)
-    Q_PROPERTY(QCategoryAxis *axisZ READ axisZ WRITE setAxisZ)
+    Q_PROPERTY(QCategoryAxis *rowAxis READ rowAxis WRITE setRowAxis)
+    Q_PROPERTY(QValueAxis *valueAxis READ valueAxis WRITE setValueAxis)
+    Q_PROPERTY(QCategoryAxis *columnAxis READ columnAxis WRITE setColumnAxis)
     Q_PROPERTY(QtDataVis3D::QDataVis::SelectionMode selectionMode READ selectionMode WRITE setSelectionMode)
     Q_PROPERTY(QtDataVis3D::QDataVis::LabelTransparency labelTransparency READ labelTransparency WRITE setLabelTransparency)
     Q_PROPERTY(QtDataVis3D::QDataVis::ShadowQuality shadowQuality READ shadowQuality WRITE setShadowQuality)
@@ -103,18 +103,18 @@ public:
     QItemModelBarDataMapping *mapping() const;
     void setMapping(QItemModelBarDataMapping *mapping);
 
-    QCategoryAxis *axisX() const;
-    void setAxisX(QCategoryAxis *axis);
-    QValueAxis *axisY() const;
-    void setAxisY(QValueAxis *axis);
-    QCategoryAxis *axisZ() const;
-    void setAxisZ(QCategoryAxis *axis);
+    QCategoryAxis *rowAxis() const;
+    void setRowAxis(QCategoryAxis *axis);
+    QValueAxis *valueAxis() const;
+    void setValueAxis(QValueAxis *axis);
+    QCategoryAxis *columnAxis() const;
+    void setColumnAxis(QCategoryAxis *axis);
 
-    // Set bar thickness. Y -component sets the thickness of z -direction.
+    // Set bar thickness.
     void setBarThickness(qreal thicknessRatio);
     qreal barThickness();
 
-    // Set spacing between bars. Y -component sets the spacing of z -direction.
+    // Set spacing between bars. Y-component sets the spacing of Z-direction.
     // If spacing is relative, 0.0f means side-to-side and 1.0f = one thickness in between.
     void setBarSpacing(QSizeF spacing);
     QSizeF barSpacing();