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I have written a simple program that (try to:-)) draws a simple triangle on a PainterDevice. The drawing occurs in a paintEvent() routine but I get the following errors at runtime:
1) a message like "painter can only be initialized as a response to a paintEvent". Ok but my paintings are indeed in the paintEvent() routine, so what?
2) another message "painter is not active" BUT if I add a this->painter.begin(this) I get a message "painter is already active".
What is important is that nothing is drawn, which is my problem now.
A last question: how can I draw that spline with Qt4???
Could anybody help?
Thanks in advance.
Below is my code (can send the complete archive if necessary).
///////////////////////////////////////////////////////////////////////////////
// File : vadSpline.h //
///////////////////////////////////////////////////////////////////////////////
#ifndef _VAD_SPLINE_H
#define _VAD_SPLINE_H
#include <vadVisualization.h>
#define XSIZE 400
#define YSIZE 400
/** vadSpline est un exemple de classe pour la visualisation d'informations
dans le projet de VAD, qui implemente le dessin d'une spline.
class vadSpline : public vadVisualization
Q_OBJECT
public:
vadSpline(QAbstractItemModel *model, vad *app=NULL, QWidget *parent=NULL, int xsize=XSIZE, int ysize=YSIZE, char *name=NULL, int debug=0);
protected slots:
void paintEvent(QPaintEvent *e);
private:
QPolygon polygon;
#endif
///////////////////////////////////////////////////////////////////////////////
// File : vadSpline.cxx //
///////////////////////////////////////////////////////////////////////////////
#include "vadSpline.h"
vadSpline::vadSpline(QAbstractItemModel *model, vad *app, QWidget *parent, int xsize, int ysize, char *name, int debug)
: vadVisualization(model, app, parent, xsize, ysize, name, debug)
this->setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysO ff);
this->setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff );
this->show();
vadSpline: aintEvent(QPaintEvent *event)
this->polygon.setPoints(3,
this->model()->data(this->model()->index(0, 0)).toInt(),
this->model()->data(this->model()->index(0, 1)).toInt(),
this->model()->data(this->model()->index(1, 0)).toInt(),
this->model()->data(this->model()->index(1, 1)).toInt(),
this->model()->data(this->model()->index(2, 0)).toInt(),
this->model()->data(this->model()->index(2, 1)).toInt()
printf("painter active ? %d\n", this->painter->isActive() ? 1 : 0);
this->painter->setWindow(0, 0, 100, 100);
this->painter->drawPolygon(this->polygon);
///////////////////////////////////////////////////////////////////////////////
// File : vadVisualization.h //
///////////////////////////////////////////////////////////////////////////////
#ifndef _VAD_VISUALIZATION_H
#define _VAD_VISUALIZATION_H
#include <qabstractitemview.h>
#include <qpainter.h>
#include <visCore.h>
//#include "vad.h"
#define SIZE 400
//class vad;
#define vad QApplication
/** vadVisualization est la classe generique pour la visualisation
d'informations dans le projet de VAD.
Le principe retenu est celui du mapping de variables sur 1, 2 ou 3
axes. Ces axes ne sont pas obligatoirement les axes d'un repère nD
classique et chaque sous-classe est libre d'utiliser ce mapping a
sa facon, y compris de ne pas l'utiliser si ce n'est pas approprie.
L'objectif etait de factoriser ici certaines fonctionnalites communes
a la plupart des techniques de visualisation d'information, afin
d'asssurer coherence et gain de temps pour les developpeurs.
L'affectation des variables aux axes est effectuee par les methodes
SetXdimension(), SetYdimension() et SetZdimension().
class vadVisualization : public QAbstractItemView, public visCore
Q_OBJECT
public:
vadVisualization(QAbstractItemModel *model, vad *app=NULL, QWidget *parent=NULL, int xsize=SIZE, int ysize=SIZE, char *name=NULL, int debug=0);
/// Acces a l'application.
visGetMacro(Vad, vad *);
protected:
/// Les fonctions ci-dessous sont des pures virtuelles, qu'il est donc necessaire de definir.
/// Pour l'instant leur definition est plus que sommaire, en fait uniquement dans le but de passer la compilation.
/// Voir la doc de Qt pour les definitions.
QRect visualRect(const QModelIndex &index) const {
return QRect(0, 0, this->width(), this->height());
void scrollTo(const QModelIndex &index, QAbstractItemView::ScrollHint hint=QAbstractItemView::EnsureVisible) {};
QModelIndex indexAt(const QPoint&) const {
return QModelIndex();
QModelIndex moveCursor(QAbstractItemView::CursorAction cursorAction, Qt::KeyboardModifiers modifiers) {
return QModelIndex();
int horizontalOffset() const {return 0;};
int verticalOffset() const {return 0;};
bool isIndexHidden(const QModelIndex &index) const {return FALSE;};
void setSelection(const QRect &rect, QItemSelectionModel::SelectionFlags flags) {};
QRegion visualRegionForSelection(const QItemSelection &selection) const {
return QRect(0, 0, this->width(), this->height());
/// Un painter pour le dessin.
QPainter *painter;
#endif
///////////////////////////////////////////////////////////////////////////////
// File : vadVisualization.cxx //
///////////////////////////////////////////////////////////////////////////////
#include "vadVisualization.h"
#define SUBFRAMEMARGIN 2
vadVisualization::vadVisualization(QAbstractItemMo del *model, vad *app, QWidget *parent, int xsize, int ysize, char *name, int debug)
: QAbstractItemView(parent)
this->setModel(model);
this->SetDebug(debug);
// la taille est determinee par l'application au sein de laquelle la visualisation s'insere
// sinon sa taille est determinee par les parametres d'initialisation
// this->Trace("1 size : %d %d", this->width(), this->height());
// if (app == NULL)
this->QWidget::setFixedSize(QSize(xsize, ysize));
// else
// app->Register(this);
// this->Trace("2 size : %d %d", this->width(), this->height());
// le style des fenetres
this->setFrameStyle(QFrame::Raised | QFrame::Panel);
this->setLineWidth(SUBFRAMEMARGIN);
// this->SetVad(app);
// this->Trace("3 size : %d %d", this->width(), this->height());
this->painter = new QPainter(this);
that was the first implementation I had made. I have once again modified the code so as to create the painter within the paintEvent() routine, the new code and the runtime error message are copy pasted below:
///////////////////////////////////////////////////////////////////////////////
// File : vadSpline.cxx //
// Author : Wilfrid LEFER //
// Comment : Exemple de classe concrete pour la visualisation dans //
// VAD //
// Related file : vadSpline.h //
// Master Technologies de l'Internet - VAD - 2006 //
///////////////////////////////////////////////////////////////////////////////
#include "vadSpline.h"
vadSpline::vadSpline(QAbstractItemModel *model, vad *app, QWidget *parent, int xsize, int ysize, char *name, int debug)
: vadVisualization(model, app, parent, xsize, ysize, name, debug)
this->setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysO ff);
this->setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff );
this->show();
vadSpline: aintEvent(QPaintEvent *event)
this->polygon.setPoints(3,
this->model()->data(this->model()->index(0, 0)).toInt(),
this->model()->data(this->model()->index(0, 1)).toInt(),
this->model()->data(this->model()->index(1, 0)).toInt(),
this->model()->data(this->model()->index(1, 1)).toInt(),
this->model()->data(this->model()->index(2, 0)).toInt(),
this->model()->data(this->model()->index(2, 1)).toInt()
QPainter painter(this);
printf("painter active ? %d\n", painter.isActive() ? 1 : 0);
painter.setWindow(0, 0, 100, 100);
painter.drawPolygon(this->polygon);
///////////////////////////////////////
Error message at run time
//////////////////////////////////////
QPainter::begin: Widget painting can only begin as a result of a paintEvent
painter active ? 0
QPainter::setWindow(), painter not active
QPainter::begin: Widget painting can only begin as a result of a paintEvent
painter active ? 0
QPainter::setWindow(), painter not active
What is surprising is that the painter is not active (painter.isActive() return FALSE) but if I add a painter.begin(this) command just after the painter has been created I get another error "painter is already active"!
So what does the message "QPainter::begin: Widget painting can only begin as a result of a paintEvent" mean? Is it a mistake in the way I define the paintEvent() slot? Should I connect this slot with any signal explicitely?
Regards. No, I do not invoke paintEvent() anywhere. I have tried to declare it as public slot, public, virtual or non virtual, nothing change.
I can send you the complete source if you want. No, just one painter but I have fixed the problem: the painter creation line must be:
QPainter painter(this->viewport());
instead of:
QPainter painter(this);
I do not know why it is necessary to refer to the viewport here, may be because I invoke setWindow()?
Anyway, thanks for having spent time to help me.
Regards. void QAbstractScrollArea::paintEvent ( QPaintEvent * event ) [virtual protected]
This event handler can be reimplemented in a subclass to receive paint events (passed in event), for the viewport() widget.
Note: If you open a painter, make sure to open it on the viewport().