How to draw over an old picture in QGraphicsScene

[Mikeeeeee]

Found such class. Is it possible to make it not the main class?
.h

#ifndef WIDGET_H
#define WIDGET_H

#include <QWidget>
#include <QPainter>
#include <QMouseEvent>
#include <QEvent>
#include <QFileDialog>
#include <QImage>
#include <QPixmap>

namespace Ui {
class Widget;
}

class Widget : public QWidget
{
    Q_OBJECT
public:
    explicit Widget(QWidget *parent = 0);
    ~Widget();
    bool eventFilter(QObject *obj, QEvent *event);

private slots:
    void on_open_clicked();

    void on_save_clicked();

    void on_R_valueChanged(int value);

    void on_G_valueChanged(int value);

    void on_B_valueChanged(int value);

    void on_pen_dial_valueChanged(int value);

    void on_pushButton_8_clicked();

private:
    QPen pen;
    QPen pen2;
    QPixmap pixmap;
    QPixmap pixman;
    QPoint lastPoint;
    int r;
    int g;
    int b;
    Ui::Widget *ui;
};

#endif // WIDGET_H

.cpp

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


Widget::Widget(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::Widget)
{
    ui->setupUi(this);
    pixmap = QPixmap(ui->label->width(),ui->label->height());
    pixmap.fill();
    pen = QPen( QBrush( Qt::black), 5.0f );
    r = 0;
    g = 0;
    b = 0;

    ui->label->setPixmap(pixmap);

    ui->label->installEventFilter(this);
    ui->red_color->installEventFilter(this);
    ui->orange_color->installEventFilter(this);
    ui->yellow_color->installEventFilter(this);
    ui->green_color->installEventFilter(this);
    ui->blue_color->installEventFilter(this);
    ui->purple_color->installEventFilter(this);
    ui->pushButton_8->installEventFilter(this);
    ui->R->installEventFilter(this);
    ui->G->installEventFilter(this);
    ui->B->installEventFilter(this);
    ui->setcolor->installEventFilter(this);
    ui->pen_dial->installEventFilter(this);
    ui->clear_pixmap->installEventFilter(this);


    ui->red_color->setStyleSheet("Background-color: red;");
    ui->orange_color->setStyleSheet("Background-color: #ffa500");
    ui->yellow_color->setStyleSheet("Background-color: yellow");
    ui->green_color->setStyleSheet("Background-color: green");
    ui->blue_color->setStyleSheet("Background-color: blue");
    ui->purple_color->setStyleSheet("Background-color: #C400AB");

    pen2 = QPen(QBrush(Qt::black), 61.0f);
    QBrush st(QColor(Qt::black),Qt::Dense7Pattern);
    pixman = QPixmap(ui->label_3->width(),ui->label_3->height());
    pixman.fill();
    QPainter p2(&pixman);
    p2.setPen(Qt::SolidLine);
    p2.setBrush(st);
    p2.drawRect(0,0,ui->label_3->width(),ui->label_3->height());
    p2.end();
    ui->label_3->setPixmap(pixman);
    
    //this->setFixedSize(this->width(), this->height());
}

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

bool Widget::eventFilter(QObject *obj, QEvent *event)
{
    if(obj == ui->label and event->type() == QEvent::MouseButtonPress)
    {
        QMouseEvent *mous = (QMouseEvent*)event;
        QPainter p(&pixmap);
        p.setPen(pen);
        p.drawPoint(mous->pos());
        p.end();
        lastPoint = mous->pos();
        ui->label->setPixmap(pixmap);
    }
    if(obj == ui->label and event->type() == QEvent::MouseMove)
    {
        QMouseEvent *mous = (QMouseEvent*)event;
        QPainter p(&pixmap);
        p.setPen(pen);
        p.drawLine(lastPoint,mous->pos());
        p.end();
        lastPoint = mous->pos();
        ui->label->setPixmap(pixmap);
    }
    if(obj == ui->red_color and event->type() == QEvent::MouseButtonPress) pen.setColor(Qt::red);
    if(obj == ui->orange_color and event->type() == QEvent::MouseButtonPress) pen.setColor(QColor(255, 128, 0));
    if(obj == ui->yellow_color and event->type() == QEvent::MouseButtonPress) pen.setColor(Qt::yellow);
    if(obj == ui->green_color and event->type() == QEvent::MouseButtonPress) pen.setColor(Qt::green);
    if(obj == ui->blue_color and event->type() == QEvent::MouseButtonPress) pen.setColor(Qt::blue);
    if(obj == ui->purple_color and event->type() == QEvent::MouseButtonPress) pen.setColor(QColor(196, 0, 171));
    if(obj == ui->setcolor and event->type() == QEvent::MouseButtonPress)
    {
        bool ok = true;
        r = ui->lineEdit->text().toInt(&ok,10);
        g = ui->lineEdit_2->text().toInt(&ok,10);
        b = ui->lineEdit_3->text().toInt(&ok,10);
        if((r <= 255 or g <= 255 or b <= 255)) pen.setColor(QColor(r,g,b));
        else ui->info->text() = "Введены неверные значения";
    }
    if(obj == ui->pen_dial and event->type() == QEvent::MouseButtonPress and QEvent::MouseMove)
    {
    }
    if(obj == ui->clear_pixmap and event->type() == QEvent::MouseButtonPress)
    {
        pixmap.fill(QColor(Qt::white));
        ui->label->setPixmap(pixmap);
    }
    if(obj == ui->label_3 and event->type() == QEvent::MouseButtonPress)
    {
        pen.setBrush(Qt::Dense5Pattern);
        ui->label->setPixmap(pixmap);
    }
}

void Widget::on_open_clicked()
{
    QString file;
    file = QFileDialog::getOpenFileName(this,tr("Открыть файл"),tr("Картинка.jpg"),tr("JPG (*.jpg)"));
    pixmap.load(file);
}

void Widget::on_save_clicked()
{
    QString file;
    file = QFileDialog::getSaveFileName(this,tr("Сохранить файл"),tr("Картинка.jpg"),tr("JPG (*.jpg"));
    pixmap.save(file);
}

void Widget::on_R_valueChanged(int value)
{
    pen.setColor(QColor(value,ui->B->value(),ui->G->value()));
    ui->Value_1->setNum(value);
}

void Widget::on_G_valueChanged(int value)
{
    pen.setColor(QColor(ui->R->value(),value,ui->G->value()));
    ui->Value_2->setNum(value);
}

void Widget::on_B_valueChanged(int value)
{
    pen.setColor(QColor(ui->R->value(),ui->B->value(),value));
    ui->Value_3->setNum(value);
}

void Widget::on_pen_dial_valueChanged(int value)
{
    pen.setWidthF(value);
    ui->label_2->setNum(value);
}

void Widget::on_pushButton_8_clicked()
{

}

[jsulm]

@Mikeeeeee said in How to draw over an old picture in QGraphicsScene:

Is it possible to make it not the main class?

I don't understand this question.
What is a "main class"?

[Mikeeeeee]

I have a MainWindow class, class for QLabel the ImageViewer. How to use the widget class code to draw in ImageViewer?

[jsulm]

@Mikeeeeee said in How to draw over an old picture in QGraphicsScene:

How to use the widget class code to draw in ImageViewer?

Like any other widget

[Mikeeeeee]

But how? Do I have to transfer the code of their Widget class to the MainWindow class ?

[jsulm]

@Mikeeeeee You have to include the header file of that widget in your MainWindow, C++ basics.

[Mikeeeeee]

It's not that simple. The class addresses .ui . I didn't create the right label in the designer. And main.cpp I have not created a class object and cannot access "this".

[jsulm]

@Mikeeeeee Then change the code of that class, so it does not use .ui file (add needed widgets manually).
"And main.cpp I have not created a class object and cannot access "this"" - well, you have to create an instance of the widget, how else do you want to use it?

[Mikeeeeee]

I decided to transfer the functionality of the class to the class "MainWindow". The "Image Viewer" class has the function "bool Image Viewer::eventFilter(QObject *obj, QEvent *event)". In the class "MainWindow" I need a function to draw "bool eventFilter(QObject obj, QEvent event);" if I add it I get an error: "undefined reference to `MainWindow::eventFilter(QObject, QEvent)'". How can this be corrected?

[jsulm]

@Mikeeeeee said in How to draw over an old picture in QGraphicsScene:

How can this be corrected?

Well, you have to define MainWindow::eventFilter(QObject, QEvent)...

[Mikeeeeee]

I append 2 images on QLabel

    QImage mapImage(":/Images/Images/mapMain.png");
    myImageViewer->setImage(mapImage);
    QImage base(":/Images/Images/mapMain.png"); // set to some file/size
    QImage overlay(":/Images/Images/mapTop.png");  // set to some file/size
    QPainter paint(&base);
    paint.drawImage(0,0,overlay);
    myImageViewer->imageLabel->setPixmap(QPixmap::fromImage(base));
    ui->verticalLayout->addWidget(myImageViewer);

    //Pen
    myPen.setWidth(20);
    myPen.setColor(Qt::green);
    //myPen.setColor(QColor(255, 0, 0, 10));
    myPen.setCapStyle(Qt::RoundCap);
    myPen.setStyle(Qt::SolidLine);
    myImageViewer->installEventFilter(this);

In the Mainwindow constructor, I wrote:

    QPixmap myPixmap;
    QPen myPen;
    QPoint lastPoint;
    bool eventFilter(QObject *obj, QEvent *event);

And wrote such eventFilter:

bool MainWindow::eventFilter(QObject *obj, QEvent *event)
{
    qDebug()<<"eventFilter";
    if(obj == myImageViewer and event->type() == QEvent::MouseButtonPress)
    {
        qDebug()<<" QEvent::MouseButtonPress";
        QMouseEvent *mous = (QMouseEvent*)event;
        QPainter p(&myPixmap);
        p.setPen(myPen);
        p.drawPoint(mous->pos());
        p.end();
        lastPoint = mous->pos();
        myImageViewer->imageLabel->setPixmap(myPixmap);
    }
    if(obj == myImageViewer and event->type() == QEvent::MouseMove)
    {
        QMouseEvent *mous = (QMouseEvent*)event;
        QPainter p(&myPixmap);
        p.setPen(myPen);
        p.drawLine(lastPoint,mous->pos());
        p.end();
        lastPoint = mous->pos();
        myImageViewer->imageLabel->setPixmap(myPixmap);
    }
}

When eventfilter is triggered, the picture disappears and a white screen appears. And Qt gives an error message:

QEvent::MouseButtonPress
QPainter::begin: Paint device returned engine == 0, type: 2
QPainter::setPen: Painter not active
QPainter::drawPoints: Painter not active
QPainter::end: Painter not active, aborted

[jsulm]

@Mikeeeeee Why do you paint in eventFilter?!
You already were told to paint in paintEvent.
In eventFilter you only store needed information (like x/y).

[Mikeeeeee]

But in the example that I showed you drawing eventfilter occurs, and if you do so, then paintEvent works only a couple of times and then for some reason no longer works.

void MainWindow::paintEvent(QPaintEvent *event)
{
    qDebug()<<"paintEvent";
}

[jsulm]

@Mikeeeeee After getting new coordinates you can call https://doc.qt.io/qt-5/qwidget.html#update to trigger paint event.

[Mikeeeeee]

It turns out to draw in eventFilter, but it was necessary to add this line to the constructor.

myPixmap  = QPixmap(myImageViewer->image.width(),myImageViewer->image.height());

I draw so:

bool MainWindow::eventFilter(QObject *obj, QEvent *event)
{
    if(obj == myImageViewer and event->type() == QEvent::MouseButtonPress)
    {
        qDebug()<<" QEvent::MouseButtonPress";
        QMouseEvent *mous = (QMouseEvent*)event;
        QPainter p(&myPixmap);
        p.setPen(myPen);
        p.drawPoint(mous->pos());
        p.end();
        lastPoint = mous->pos();
        myImageViewer->imageLabel->setPixmap(myPixmap);
    }
}

But when drawing the picture disappears and the screen turns black. How to fix? Can I set the drawing on the QImage overlay(":/Images/Images/mapTop.png");?

[Mikeeeeee]

And if I do so, the screen becomes white.

myPixmap.fill();

How to make myPixmap transparent?

[mrjj]

myPixmap.fill(Qt::transparent);

[Mikeeeeee]

Thanks. Do so:

    myPixmap  = QPixmap(myImageViewer->image.width(),myImageViewer->image.height());
    myPixmap.fill(Qt::transparent);
    myPixmap = QPixmap(":/Images/Images/mapTop.png");

But after drawing the picture disappears :

myImageViewer->setImage(mapImage);

How to get myPixmap the images:":/Images/Images/mapMain.png" and ":/Images/Images/mapTop.png" , but draw only on:
":/Images/Images/mapTop.png"?

[mrjj]

@Mikeeeeee
You mean draw myPixmap on mapImage and then
show the combined image with myImageViewer->setImage(mapImage); ?
Thats like before where we combined them.

[Mikeeeeee]

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