QSvgRenderer painting problems

Question

I am trying to render a subclassed QGraphicsObject, called Part, to a QGraphicsScene.

class Part : public QGraphicsObject {
    Q_OBJECT;
public:
    Part(std::map<std::string, std::string> data, QString part_svg_file);
    void setSharedRenderer(QSvgRenderer *r);
    void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget);
    QRectF boundingRect() const;

    QGraphicsSvgItem* GetPartSvg();
    QGraphicsSvgItem* GetTerminalsSvg();
private:
    QGraphicsSvgItem *m_part_graphic;
    QGraphicsSvgItem *m_terminal_graphic;
    QSvgRenderer *m_svg_renderer;
    QDialog *m_dialog;
    std::map<std::string, std::string> m_data;

}; // class Part

This part contains two QGraphicsSvgItems. These two items are generated from the same SVG file upon construction of Part:

Part::Part(std::map<std::string, std::string> data, QString part_svg_file) 
    : m_terminal_graphic(new QGraphicsSvgItem(part_svg_file)),
      m_part_graphic(new QGraphicsSvgItem(part_svg_file)),
      m_svg_renderer(new QSvgRenderer())
{
    m_part_graphic->setElementId("part");
    m_terminal_graphic->setElementId("terminals");
}

There are two items as the SVG contains two groups, one called "part" and the other called "terminals"

I want these two items to be rendered to the QGraphicsScene, I have them in seperate QGraphicsSvgItems to allow me to turn the "terminals" group off in certain instances.

I though the proper way to do this was to render them in the paint event of my parent QGraphicsObject class. However, this is not working.

void Part::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget) {
    painter->setPen(Qt::PenStyle::SolidLine);
    painter->setPen(Qt::black);
    painter->setBrush(Qt::SolidPattern);
    painter->setBrush(Qt::black);
    painter->drawRect(0, 0, 25, 25);
    m_part_graphic->setSharedRenderer(m_svg_renderer);
    m_svg_renderer->render(painter);
}

I am drawing a simple rectangle to ensure that the paint event is getting called properly. The rectangle is being drawn on the scene in the appropriate place. The QGraphicsSvgItem, m_part_graphic, is not being drawn on the scene. What is the proper way to do this?

To recap, I want to draw two different QGraphicsSvgItems onto a QGraphicsScene as part of a larger class called "Part".

---

UPDATE

At the suggestion below, I started a new project and began with a basic graphicsview render of an SVG.

m_svg_item = new QGraphicsSvgItem("C:\\Code\\QT_Testing\\QT_Testing\\Resources\\bubbles.svg");
m_svg_item->setFlags(QGraphicsItem::ItemClipsToShape);
m_svg_item->setZValue(0);

s->addItem(m_svg_item);

If I remove the s->addItem(m_svg_item); line, it compiles and runs fine. Obviously doesn't draw the SVG at that point either.

It is crashing and giving me the follwing: (MS Visual Studio Pro 2012)

Output Window:

ASSERT failure in QCoreApplication::sendEvent: "Cannot send events to objects owned by a different thread. Current thread 3f0730. Receiver '' (of type 'QGraphicsSvgItem') was created in thread 3ff0a0", file kernel\qcoreapplication.cpp, line 535 Debug Error!

Program: C:\QT\4.8.5\bin\QtCored4.dll Module: 4.8.5 File: global\qglobal.cpp Line: 2303

ASSERT failure in QCoreApplication::sendEvent: "Cannot send events to objects owned by a different thread. Current thread 3f0730. Receiver '' (of type 'QGraphicsSvgItem') was created in thread 3ff0a0", file kernel\qcoreapplication.cpp, line 535

And the Call Stack:

msvcr110d.dll!_CrtIsValidHeapPointer(const void * pUserData=0x004a76b0) Line 2036   C++
msvcr110d.dll!_free_dbg_nolock(void * pUserData=0x004a76b0, int nBlockUse=0) Line 1322  C++
msvcr110d.dll!_free_dbg(void * pUserData=0x004a76b0, int nBlockUse=0) Line 1265 C++
msvcr110d.dll!operator delete(void * pUserData=0x004a76b0) Line 54  C++
QtGuid4.dll!QGradientBrushData::`scalar deleting destructor'(unsigned int)  C++
QtGuid4.dll!QBrushDataPointerDeleter::deleteData(QBrushData * d=0x004a76b0) Line 247    C++
QtGuid4.dll!QBrushDataPointerDeleter::cleanup(QBrushData * d=0x004a76b0) Line 257   C++
QtGuid4.dll!QScopedPointer<QBrushData,QBrushDataPointerDeleter>::reset(QBrushData * other=0x00432f38) Line 149  C++
QtGuid4.dll!QBrush::operator=(const QBrush & b={...}) Line 636  C++

---

main.cpp:

#include "qt_testing.h"
#include <QtGui/QApplication>


int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QT_Testing w;
    w.show();
    return a.exec();
}

qt_testing.cpp:

#include "qt_testing.h"
#include "svgview.h"

#include <QtGui>

QT_Testing::QT_Testing(QWidget *parent)
    : QMainWindow(parent),
      m_view(new SvgView)
{
    setCentralWidget(m_view);
    setWindowTitle("SVG Viewer");
}

QT_Testing::~QT_Testing()
{

}

void QT_Testing::openFile(const QString &path) {
    QString file_name;

}

void QT_Testing::setRenderer(QAction *action) {

}

svgview.cpp:

#include "svgview.h"

#include <qfile.h>
#include <QtGui>
#include <QtSvg\qgraphicssvgitem.h>

SvgView::SvgView(QWidget *parent)
    : QGraphicsView(parent)
    , m_renderer(Native)
    , m_svg_item(0)
    , m_background_item(0)
    , m_outline_item(0)
{
    setScene(new QGraphicsScene(this));
    setTransformationAnchor(AnchorUnderMouse);
    setDragMode(ScrollHandDrag);
    setViewportUpdateMode(FullViewportUpdate);

    QPixmap tile_pixmap(64, 64);
    tile_pixmap.fill(Qt::white);
    QPainter tile_painter(&tile_pixmap);
    QColor color(220, 220, 220);
    tile_painter.fillRect(0, 0, 32, 32, color);
    tile_painter.fillRect(32, 32, 32,32, color);
    tile_painter.end();

    setBackgroundBrush(tile_pixmap);

    QGraphicsScene *s = scene();

    s->clear();
    resetTransform();

    m_svg_item = new QGraphicsSvgItem("C:\\Code\\QT_Testing\\QT_Testing\\Resources\\bubbles.svg");
    m_svg_item->setFlags(QGraphicsItem::ItemClipsToShape);
    m_svg_item->setCacheMode(QGraphicsItem::NoCache);
    m_svg_item->setZValue(0);

    /*m_background_item = new QGraphicsRectItem(QRect(0, 0, 300, 300));
    m_background_item->setBrush(Qt::white);
    m_background_item->setPen(Qt::NoPen);
    m_background_item->setVisible(true);
    m_background_item->setZValue(-1);*/

    //s->addItem(m_background_item);
    s->addItem(m_svg_item);

    s->addEllipse(150, 150, 100, 100, QPen(Qt::black, Qt::PenStyle::SolidLine));

    s->setSceneRect(-10, -10, 320, 320);
}

void SvgView::drawBackground(QPainter *p, const QRectF &) {
    p->save();
    p->resetTransform();
    p->drawTiledPixmap(viewport()->rect(), backgroundBrush().texture());
    p->restore();


}

void SvgView::paintEvent(QPaintEvent *event) {
    QGraphicsView::paintEvent(event);
}

void SvgView::wheelEvent(QWheelEvent *event) {
    qreal factor = qPow(1.2, event->delta() / 240.0);
    scale(factor, factor);
    event->accept();
}

Answer 1

As much as I hate this answer, here is what I did to fix this. Since QT 4.8.5 is not officially supported in Visual Studio 2012, I wiped my QT install completely and installed QT 5.2.1. After fixing a few include paths, the above code compiled and ran just fine. The SVGs are now drawing as expected. Thank you Kuba Ober for your help. It is much appreciated.