Draw line on image using QPainter

[Qt Coder]

It's already showing DoorControl1 Dialog with Plane's image...

still as you said I added ODoorControl1->show(); in Bifold constructor ,but no line still drawn..

[high_flyer]

you have to simplify and go step at a time.
Put your dialog in main, and show it.
See if you get the line drawn then.

[Qt Coder]

I have added draw line code in main.cpp itself but still it only shows image and no line is drawn

main.cpp

#include <QtGui/QApplication>
 
#include <QtCore>
#include <QtGui>
#include <QLabel>
//#include "bifold.h"
 
 
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
 
   // BiFold w;
  //  w.show();
    QLabel l;
    QPixmap pixmap(500,500);
    pixmap.load(QString::fromUtf8(":/BiFold/Images/Plane.PNG"));
 
    QPainter painter(&pixmap);
    l.resize(pixmap.size());
 
 
    QPen Red((QColor::QColor(255,0,0)),1);
    painter.setPen(Red);
    painter.drawLine(250,300,500,300);
    painter.end();
    l.setPixmap(pixmap);
    l.show();
    return a.exec();
}

#include <QtGui/QApplication>

#include <QtCore>
#include <QtGui>
#include <QLabel>
//#include "bifold.h"


int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

   // BiFold w;
  //  w.show();
    QLabel l;
    QPixmap pixmap(500,500);
    pixmap.load(QString::fromUtf8(":/BiFold/Images/Plane.PNG"));

    QPainter painter(&pixmap);
    l.resize(pixmap.size());


    QPen Red((QColor::QColor(255,0,0)),1);
    painter.setPen(Red);
    painter.drawLine(250,300,500,300);
    painter.end();
    l.setPixmap(pixmap);
    l.show();
    return a.exec();
}

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[Qt Coder]

Is this a fault of my image,but I tried changing the image still no line is drawn..

I read in documentation of QPainter "Painting on a QImage with the format QImage::Format_Indexed8 is not supported."


But my image format is QImage::Format_RGB32.


I m not able to upload image here,it says "upload failed"


pls show me right direction ,I cannot proceed my work if this issues is not solved.

[ChrisW67]

Are you sure that your resource file path is good?

Your code with some minor tweaks and a local file:

#include <QtCore>
#include <QtGui>
#include <QDebug>
 
int main(int argc, char *argv[])
{ 
    QApplication app(argc, argv);
 
    QLabel l;
    QPixmap pixmap;
 
    bool goodLoad = pixmap.load(QString::fromUtf8("./test.png"));
    qDebug() << goodLoad << pixmap.isNull() << pixmap.size() << pixmap.depth();
 
    QPainter painter(&pixmap);
    QPen Red((QColor::QColor(255,0,0)),1);
    painter.setPen(Red);
    painter.drawLine(40, 40, 200, 280);
    painter.end();
 
    pixmap.save("./test2.png");
 
    l.setPixmap(pixmap);
    l.show();
 
    return app.exec();
}

#include <QtCore>
#include <QtGui>
#include <QDebug>

int main(int argc, char *argv[])
{ 
    QApplication app(argc, argv);

    QLabel l;
    QPixmap pixmap;

    bool goodLoad = pixmap.load(QString::fromUtf8("./test.png"));
    qDebug() << goodLoad << pixmap.isNull() << pixmap.size() << pixmap.depth();

    QPainter painter(&pixmap);
    QPen Red((QColor::QColor(255,0,0)),1);
    painter.setPen(Red);
    painter.drawLine(40, 40, 200, 280);
    painter.end();

    pixmap.save("./test2.png");

    l.setPixmap(pixmap);
    l.show();

    return app.exec();
}

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Input is:
test.jpg
Output is:

true false QSize(240, 320) 24

true false QSize(240, 320) 24

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and
test2.jpg

Edit: the forum converted the PNG files to JPG

[Qt Coder]

Finally the line is visible over the image

The co-ordinates I used for drawing line were main culprit here
painter.drawLine(250,300,500,300);

also
 
 qDebug() << goodLoad << pixmap.isNull() << pixmap.size() << pixmap.depth();
 
shows
 
true false QSize(533, 292) 32

also

 qDebug() << goodLoad << pixmap.isNull() << pixmap.size() << pixmap.depth();

shows

true false QSize(533, 292) 32

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if I use ur co-ordinate,

painter.drawLine(40, 40, 200, 280);

line is drawn.....

[Qt Coder]

My next query is

Can we directly paint QDialog ?

I need to draw some arcs, squares and lines on QDialog

[high_flyer]

You can paint on any widget, but only in a paintEvent().

[Manobala]

hai to every one am new to qt actually am trying to draw line on image (qpixmap),i had tried all coeds u have given above but still i didnt get the result plz can any one give full code to me thanking you and sorry for my bad english

[cskumar]

How to drag that line over the image?
I tried to drag. But it does not update.