Error messages from QPainter

[Perdrix]

QPainter::begin: Paint device returned engine == 0, type: 2
QPainter::setRenderHint: Painter must be active to set rendering hints
QPainter::setRenderHint: Painter must be active to set rendering hints
QPainter::save: Painter not active
QPainter::translate: Painter not active
QPainter::scale: Painter not active
QPainter::translate: Painter not active
QPainter::restore: Unbalanced save/restore
QPainter::end: Painter not active, aborted

What are the most likely causes?

[jsulm]

@Perdrix said in Error messages from QPainter:

What are the most likely causes?

Probably issues in your code which you did not post...

[Perdrix]

void DSSImageView::resizeEvent(QResizeEvent* e)
{
    if (nullptr != pPixmap)
    {
        const QSize sz = e->size();
        emit Image_resizeEvent(e);
        m_drawingPixmap = QPixmap(sz);
        const qreal pixWidth = pPixmap->width();
        const qreal pixHeight = pPixmap->height();
        const qreal hScale = static_cast<qreal>(sz.width()) / pixWidth;
        const qreal vScale = static_cast<qreal>(sz.height()) / pixHeight;
        m_scale = std::min(hScale, vScale);

        qreal xoffset = 0.0, yoffset = 0.0;
        if ((pixWidth * m_scale) < sz.width())
        {
            xoffset = floor((sz.width() - (pixWidth * m_scale)) / 2.0);
        }
        if ((pixHeight * m_scale) < sz.height())
        {
            yoffset = floor((sz.height() - (pixHeight * m_scale)) / 2.0);
        }
        m_origin = QPointF(xoffset, yoffset);

        displayRect.setTopLeft(m_origin);
        displayRect.setSize(QSizeF(pixWidth * m_scale, pixHeight * m_scale));

        if (m_pToolBar)
        {
            qreal width(m_pToolBar->width());
            qreal height(m_pToolBar->height());
            QPoint point(sz.width() - width, sz.height() - height);
            m_pToolBar->move(point);
        }

        drawOnPixmap();
        update();
    }
    Inherited::resizeEvent(e);
}
void DSSImageView::drawOnPixmap()
{
    ZFUNCTRACE_RUNTIME();
    if (nullptr != pPixmap)
    {
        QPainter painter(&m_drawingPixmap);
        QPalette palette{ QGuiApplication::palette() };
        QBrush brush{ palette.dark() };

        painter.setRenderHint(QPainter::Antialiasing);
        painter.setRenderHint(QPainter::SmoothPixmapTransform);
        painter.fillRect(rect(), brush);

        painter.save();
        painter.translate(m_origin);
        painter.scale(m_zoom * m_scale, m_zoom * m_scale);
        painter.translate(-m_origin);

        //
        // Draw the rectangle of interest at the origin location
        //
        painter.drawPixmap(m_origin, *pPixmap, rectOfInterest);
        painter.restore();

        //
        // Has the user enabled four corners mode?
        // 
        if (m_fourCorners)
        {
            paintFourCorners(painter);
        }
        else if (nullptr != pOverlayPixmap)
        {
            //
            // Draw the overlay image in the same way that we drew the main image
            //
            painter.save();
            painter.translate(m_origin);
            painter.scale(m_zoom * m_scale, m_zoom * m_scale);
            painter.translate(-m_origin);

            //
            // Finally draw the rectangle of interest at the origin location
            //
            painter.drawPixmap(m_origin, *pOverlayPixmap, rectOfInterest);
            painter.restore();
        }

        painter.end();
    }
}

m_drawingPixmap is a class member that is created when the class is instantiated

[mchinand]

@Perdrix said in Error messages from QPainter:

const QSize sz = e->size();

I would check to make sure that the size is not zero when this is called (i.e., that you are not trying to draw to a pixmap that has a size of (0,0)). Also, what is your Image_resizeEvent signal connected to?

[Perdrix]

That makes sense - I will look into that.

The ImageView widget is part of a dialog/Ui object created by the source file below (specifically the object called "picture"):

<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
 <class>StackingDlg</class>
 <widget class="QWidget" name="StackingDlg">
  <property name="geometry">
   <rect>
    <x>0</x>
    <y>0</y>
    <width>711</width>
    <height>870</height>
   </rect>
  </property>
  <property name="sizePolicy">
   <sizepolicy hsizetype="Expanding" vsizetype="Expanding">
    <horstretch>0</horstretch>
    <verstretch>0</verstretch>
   </sizepolicy>
  </property>
  <property name="minimumSize">
   <size>
    <width>711</width>
    <height>870</height>
   </size>
  </property>
  <property name="maximumSize">
   <size>
    <width>16777215</width>
    <height>16777215</height>
   </size>
  </property>
  <property name="windowTitle">
   <string notr="true"/>
  </property>
  <layout class="QVBoxLayout" name="verticalLayout">
   <item>
    <widget class="QSplitter" name="splitter">
     <property name="orientation">
      <enum>Qt::Vertical</enum>
     </property>
     <widget class="QWidget" name="layoutWidget">
      <layout class="QVBoxLayout" name="verticalLayout_1">
       <item>
        <layout class="QHBoxLayout" name="horizontalLayout">
         <item>
          <widget class="QLabel" name="information">
           <property name="sizePolicy">
            <sizepolicy hsizetype="Expanding" vsizetype="Preferred">
             <horstretch>0</horstretch>
             <verstretch>0</verstretch>
            </sizepolicy>
           </property>
           <property name="minimumSize">
            <size>
             <width>275</width>
             <height>30</height>
            </size>
           </property>
           <property name="styleSheet">
            <string notr="true">background: qlineargradient(spread:pad, x1:0, y1:0, x2:1, y2:0, stop:0 rgba(138, 185, 242, 0), stop:1 rgba(138, 185, 242, 255))</string>
           </property>
           <property name="text">
            <string notr="true"/>
           </property>
          </widget>
         </item>
         <item>
          <widget class="QToolButton" name="fourCorners">
           <property name="sizePolicy">
            <sizepolicy hsizetype="Preferred" vsizetype="Preferred">
             <horstretch>0</horstretch>
             <verstretch>0</verstretch>
            </sizepolicy>
           </property>
           <property name="minimumSize">
            <size>
             <width>38</width>
             <height>38</height>
            </size>
           </property>
           <property name="maximumSize">
            <size>
             <width>64</width>
             <height>64</height>
            </size>
           </property>
           <property name="styleSheet">
            <string notr="true">border: none</string>
           </property>
           <property name="text">
            <string notr="true">...</string>
           </property>
           <property name="icon">
            <iconset resource="../resources.qrc">
             <normaloff>:/stacking/4corners.png</normaloff>:/stacking/4corners.png</iconset>
           </property>
           <property name="iconSize">
            <size>
             <width>38</width>
             <height>38</height>
            </size>
           </property>
          </widget>
         </item>
         <item>
          <widget class="QSlider" name="horizontalSlider">
           <property name="sizePolicy">
            <sizepolicy hsizetype="Preferred" vsizetype="Fixed">
             <horstretch>0</horstretch>
             <verstretch>0</verstretch>
            </sizepolicy>
           </property>
           <property name="minimumSize">
            <size>
             <width>170</width>
             <height>0</height>
            </size>
           </property>
           <property name="orientation">
            <enum>Qt::Horizontal</enum>
           </property>
          </widget>
         </item>
        </layout>
       </item>
       <item>
        <layout class="QHBoxLayout" name="horizontalLayout_2">
         <item>
          <widget class="DSSImageView" name="picture" native="true">
           <property name="sizePolicy">
            <sizepolicy hsizetype="Expanding" vsizetype="Expanding">
             <horstretch>0</horstretch>
             <verstretch>0</verstretch>
            </sizepolicy>
           </property>
           <property name="minimumSize">
            <size>
             <width>300</width>
             <height>200</height>
            </size>
           </property>
          </widget>
         </item>
        </layout>
       </item>
      </layout>
     </widget>
     <widget class="QWidget" name="layoutWidget_2">
      <layout class="QGridLayout" name="gridLayout">
       <item row="0" column="0">
        <widget class="QLabel" name="listInfo">
         <property name="minimumSize">
          <size>
           <width>0</width>
           <height>25</height>
          </size>
         </property>
         <property name="styleSheet">
          <string notr="true">background: qlineargradient(spread:pad, x1:0, y1:0, x2:1, y2:0, stop:0 rgba(138, 185, 242, 0), stop:1 rgba(138, 185, 242, 255))</string>
         </property>
         <property name="text">
          <string notr="true"/>
         </property>
        </widget>
       </item>
       <item row="1" column="0">
        <widget class="QTableView" name="tableView">
         <property name="dragDropMode">
          <enum>QAbstractItemView::DropOnly</enum>
         </property>
         <property name="selectionMode">
          <enum>QAbstractItemView::ExtendedSelection</enum>
         </property>
         <property name="selectionBehavior">
          <enum>QAbstractItemView::SelectRows</enum>
         </property>
         <property name="sortingEnabled">
          <bool>true</bool>
         </property>
         <attribute name="verticalHeaderVisible">
          <bool>false</bool>
         </attribute>
        </widget>
       </item>
       <item row="2" column="0">
        <widget class="QTabWidget" name="tabWidget">
         <property name="sizePolicy">
          <sizepolicy hsizetype="Expanding" vsizetype="Minimum">
           <horstretch>0</horstretch>
           <verstretch>0</verstretch>
          </sizepolicy>
         </property>
         <property name="minimumSize">
          <size>
           <width>0</width>
           <height>0</height>
          </size>
         </property>
         <property name="maximumSize">
          <size>
           <width>16777215</width>
           <height>25</height>
          </size>
         </property>
         <property name="tabPosition">
          <enum>QTabWidget::South</enum>
         </property>
         <property name="currentIndex">
          <number>0</number>
         </property>
         <widget class="QWidget" name="tab">
          <attribute name="title">
           <string>Main Group</string>
          </attribute>
         </widget>
        </widget>
       </item>
      </layout>
     </widget>
    </widget>
   </item>
  </layout>
 </widget>
 <customwidgets>
  <customwidget>
   <class>DSSImageView</class>
   <extends>QWidget</extends>
   <header>dssimageview.h</header>
   <container>1</container>
  </customwidget>
 </customwidgets>
 <resources>
  <include location="../resources.qrc"/>
 </resources>
 <connections/>
</ui>

that I would have expected to be autosized when the object is created in the ctor of StackingDlg:

	StackingDlg::StackingDlg(QWidget* parent) :
		QDialog(parent),
		ui(new Ui::StackingDlg),
		initialised(false)
	{
		ui->setupUi(this);

but when the dlg was displayed, it appears that no resize event had ever been sent to the picture object (I thought that was always done after a setVisible(true);) which I issued not long after the ctor from StackingDlg. If I then manually resize the problem goes away.

[Perdrix]

If I check the size of the picture object in its ctor I get a size of 100x30 which is very small - why wasn't it resized by the layout?

[SGaist]

Hi,

So long as the widget is not shown, it has no physical size hence the constructor is the wrong place to grab sizes of components.

[Perdrix]

OK, so I thought about it and put that stuff into the resizeEvent handler (with a bit of code tweaking) and that seems to work very well indeed.

Thank you for that.
D.