Draw QImage in QOpenGLWidget

[mrjj]

Update:
Oh you posted while i wrote.
Yes its correct. but if image is in sub folder, the subfolder will be include in the path.

Just a note:
Use a QRessurce file is not complicated.
The docs just start off looking complicated.

In reality, it's just

File - > New File

give it a name and press next.

Then right click in the project view, and

Point to the image file in your subfolder.

Then change code to use the syntax starting with :/
and you should be good.

[artwaw]

@Zarcoin You can however as @mrjj wrote - you can just click out this without having to write a single line of code.
Truth to tell - I never write those files, just click it out. This way you don't have to worry about typos or format ;)

[Zarcoin]

Woaw big thanks to you @mrjj for the explanation! So i did what you said, but unfortunately it's still not working. oof
As you can see here i added an rqc and my file.

and i then wrote this code:

void MapOpenGL::initializeGL(){
    bg = new QImage();
    qDebug() << QFile::exists("mulhouse.PNG");
}

void MapOpenGL::paintGL(){
    QPainter p(this);

    p.setPen(Qt::white);

    bool test = bg->load(QString(":/mulhouse.PNG"));
    if (test == false){
        p.drawLine(QLineF(10, 10, 500, 500));
        p.drawLine(QLineF(500, 10, 10, 500));
    }else{
        QRectF target( 10, 10, 409, 210);
        //QRectF source( 0.0, 0.0, 399, 200);
        p.drawImage( target, *bg);
    }
}

It still draws lines instead of the image and debug says false !
Should i add a prefix in my rqc file ? how does it work exatcely in qtcreator ?

[artwaw]

@Zarcoin your resource file seems to be empty/not include any files. However I can see you've included the png file in your project...
Right-click on the resource file, select "open editor" or similar. Then add the file to the resource file. All we said about prefixes will become self-explanatory once you open the editor I hope.

[mrjj]

@Zarcoin

Hi
Try again, you right-click the wrong place. then it adds as other files.
Right click the actual qrc file in the tree.
You can have more than one qres file so one right-clicks the one , that file should be added to.

So once you get the file to be in res "folder", you can right-click the file and take the path so its always 100% correct.

[Zarcoin]

It works ! I didn't understand that i had to create a prefix and then add the file ! after that i can indeed right click on the file and copy the path

Thank you so much to all of you for the help, you're so nice !

[Zarcoin]

For people asking the same question, here is my result (using QtCreator):

• Create a new class that extends OpenGlWidget

class MapOpenGL : public QOpenGLWidget
{
public:
    MapOpenGL( QWidget* parent = NULL);

    virtual void initializeGL();
    virtual void paintGL();
    virtual void resizeGL( int width, int heigh);
};

• In the ui, right click your OpenGLWidget, click on "promote to" and then use your new class
• then you need to add your resource in the project. File -> New File -> Qt -> Qt Resource File
• right click your qrc file and open editor. Create a prefix, then create a ressource file ( the file you wanna draw)
• In your qrc sub folder, find your image, right click and copy the path
• I then use QPainter to draw my image:

MapOpenGL::MapOpenGL( QWidget* parent) : QOpenGLWidget (parent)
{

}

void MapOpenGL::initializeGL(){
}

void MapOpenGL::paintGL(){
    QPainter p(this);
    QRectF target( 10, 10, 500, 500);
    p.drawImage( target, new QImage(QString("path_of_the_image_you_copied"));

}

For further information on how to draw, go check QPainter methods.

[SGaist]

@Zarcoin said in Draw QImage in QOpenGLWidget:

bg = new QImage();

No need to allocate QImage on the heap. You are just adding the overhead of dereferencing it in each call of paintGL.

[Zarcoin]

Yes don't worry that's what i did, i just wanted to show how it works ! But thank you tho !

[QtTester]

@Zarcoin
I never thought you can use QPainter in ::paintGL(), that's a new idea. have you compared the CPU usage with ::paintEvent() ?

[kshegunov]

@QtTester said in Draw QImage in QOpenGLWidget:

I never thought you can use QPainter in ::paintGL(), that's a new idea. have you compared the CPU usage with ::paintEvent() ?

There's no paintEvent with OpenGL widget, or specifically you shouldn't mess with it unless you want to break it. paintEvent is going to call the paintGL whenever it's ready for you to issue the draw commands or w/e. As for the CPU usage it probably is comparable.

Note: please don't do the "stand up zombie" without a good reason. I really doubt the OP will be back to answer you.