Image not displaying using QPainter drawImage

0
votes

I have an QFrame within a QWidget, in my application. When I try to draw a draw a image within the QFrame, the image is inserted only when coordinates are (0,0) and if they are something like (100,100) the image is not drawn. I created a new class for the frame and implemented paintEvent(QPaintEvent *p) in it. Is there any thing I am doing here ?

widget.h

#ifndef WIDGET_H
#define WIDGET_H

#include <QFrame>
#include <QPainter>
#include "frame.h"

class frame;
namespace Ui {
    class Widget;
}
class Widget : public QFrame
{
    Q_OBJECT
public:
    explicit Widget(QWidget *parent = 0);
    ~Widget();
private:
    Ui::Widget *ui;
    frame * f;
};
#endif // WIDGET_H

widget.cpp

#include "widget.h"
#include "ui_widget.h"

Widget::Widget(QWidget *parent) :
    QFrame(parent),
    ui(new Ui::Widget)
{
    ui->setupUi(this);
    f = new frame(ui->frame);
    f->show();
}

Widget::~Widget()
{
    delete ui;
}

frame.h

#ifndef FRAME_H
#define FRAME_H

#include <QObject>
#include <QWidget>
#include <QPainter>

class frame : public QWidget
{
    Q_OBJECT
public:
    explicit frame(QWidget *parent = 0);

protected:
    void paintEvent(QPaintEvent *p);

signals:

public slots:
};

#endif // FRAME_H

frame.cpp

#include "frame.h"

frame::frame(QWidget *parent) : QWidget(parent)
{

}

void frame::paintEvent(QPaintEvent *p)
{
    QPainter* pPainter = new QPainter(this);
    QImage img(":/left.png");
    Q_ASSERT(!img.isNull());
    QRect source(0,0,20,10);
    QRect target(50,50,20,10);
    pPainter->drawImage(target, img,source);
    QWidget::paintEvent(p);
    QWidget::update();
}

If I use QRect target(0,0,20,10) in the above code the image is drawn.

testImage.pro

QT       += core gui

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

TARGET = testImage
TEMPLATE = app

DEFINES += QT_DEPRECATED_WARNINGS

SOURCES += main.cpp\
        widget.cpp \
    frame.cpp

HEADERS  += widget.h \
    frame.h

FORMS    += widget.ui

RESOURCES += \
    src.qrc

DISTFILES +=

I am being stuck in this one for a long time, any idea will be helpful. I have tried Qt verions 5.6 and 5.8, similar result. And the OS is Lubuntu. The image resolution is 20*10. Thanks.enter image description here

2
qt

2 Answers

0
votes

Try like this:

void frame::paintEvent(QPaintEvent *p){
QPainter lPainter(this);
QPixmap lPixmap(":/left.png");
Q_ASSERT(!lPixmap.isNull());
QRect source(0,0,20,10);
QRect target(50,50,20,10);
lPainter->drawPixmap(target, lPixmap);
QWidget::paintEvent(p);}

remove update form painEvent and try to use pixmap.

0
votes

I have found a solution, I have subclassed QgraphicsView and reimplemented paint method in it,

void graphicsView::paintEvent(QPaintEvent *e)
{
  QGraphicsView::paintEvent(e);
  QPainter pPainter(this->viewport());
  QImage img(":/images/x.png");
  Q_ASSERT(!img.isNull());
  QRect target(300,230,20,10);
  pPainter.drawImage(target, img);
}