How to draw over an old picture in QGraphicsScene

[Mikeeeeee]

Hi!
I draw in QGraphicsScene
If I draw not transparent color, then I can draw on top of the old picture. If I draw with a transparent color, the non-transparent color is not visible. How to erase an old drawing when drawing?

#include "paintscene.h"


paintScene::paintScene(QObject *parent) : QGraphicsScene(parent)
{
    //myQGraphicsScene = new QGraphicsView();
    //scene = new paintScene();       // Инициализируем графическую сцену

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

}

paintScene::~paintScene()
{

}

void paintScene::mousePressEvent(QGraphicsSceneMouseEvent *event)
{
    // При нажатии кнопки мыши отрисовываем эллипс
    addEllipse(event->scenePos().x() -  myPen.width()/2,
               event->scenePos().y() -  myPen.width()/2,
               myPen.width(),
                myPen.width(),
               QPen(Qt::NoPen),
               QBrush(myPen.color()));
    // Сохраняем координаты точки нажатия
    previousPoint = event->scenePos();
    buttonIsPressed = true;
}

void paintScene::mouseMoveEvent(QGraphicsSceneMouseEvent *event)
{
    if (buttonIsPressed)
    {
        // Отрисовываем линии с использованием предыдущей координаты
        addLine(previousPoint.x(),
                previousPoint.y(),
                event->scenePos().x(),
                event->scenePos().y(),
                myPen);
        // Обновляем данные о предыдущей координате
        previousPoint = event->scenePos();
    }
}

void paintScene::mouseReleaseEvent(QGraphicsSceneMouseEvent *event)
{
    buttonIsPressed = false;
}

[Mikeeeeee]

Perhaps you need to draw not vector and pixel. But how to do it?

[Mikeeeeee]

Tried to make so , but I receive an error : QPainter::drawPoints: Painter not active. Please tell me how to fix it

void paintScene::mousePressEvent(QGraphicsSceneMouseEvent *event)
{
    myPainter.setPen(myPen);
    myPainter.drawPoint(event->scenePos().x(),event->scenePos().y());
 
}

[jsulm]

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

Please tell me how to fix it

Don't use painter in mousePressEvent, use it in paintEvent.
In mousePressEvent you only store needed information (x/y) which you then use in paintEvent.
Also, create local QPainter instance in paintEvent.

[Mikeeeeee]

Did so, but the picture is not drawn.

void paintScene::mousePressEvent(QGraphicsSceneMouseEvent *event)
{
    x = event->scenePos().x();
    y = event->scenePos().x();
}

void paintScene::paintEvent(QPaintEvent *event)
{
    QPainter myPainter; 
    myPainter.setPen(myPen);
    myPainter.drawPoint(x,y);
}

void paintScene::paintEvent(QPaintEvent *event) does not work.

[Mikeeeeee]

and if I prescribe void paintEvent(QPaintEvent *event); to the main class, it automatically fires 1 time when the application is loaded, 1 time when the left mouse button is pressed and no longer works.

[Mikeeeeee]

I did it in the main class. but get the same error:
QPainter::setPen: Painter not active
QPainter::drawPoints: Painter not active

void Paint::paintEvent(QPaintEvent *event)
{
    Q_UNUSED(event);
    QPen myPen;
    myPen.setWidth(20);
    myPen.setColor(Qt::green);
    //myPen.setColor(QColor(255, 0, 0, 10));
    myPen.setCapStyle(Qt::RoundCap);
    myPen.setStyle(Qt::SolidLine);

    QPainter myPainter; // Создаём объект отрисовщика
    myPainter.setPen(myPen);
    myPainter.drawPoint(scene->x,scene->y);
    myPainter.drawEllipse(scene->x, scene->y, scene->x+50, scene->x+50);
    qDebug()<<scene->x<<scene->y;
}

[mrjj]

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

QPainter myPainter; // Со

it should be
QPainter myPainter(this);

[Mikeeeeee]

If I do so in a class inherited from QGraphicsScene, I get an error: no matching constructor for initialization of 'QPainter'
and if I prescribe void paintEvent(QPaintEvent *event); to the main class, it automatically fires 1 time when the application is loaded, 1 time when the left mouse button is pressed and no longer works.

[mrjj]

@Mikeeeeee
QGraphicsScene do not have paintEvent so that is why its not working.
Normally one would use a custom widget and simply insert into scene.

[Mikeeeeee]

Made such class.
How to add x and y coordinates?
How to call void widgetForPainter::paintEvent(QPaintEvent *event) when clicking on a widget?

.h

#ifndef WIDGETFORPAINTER_H
#define WIDGETFORPAINTER_H

#include "QWidget"
#include "QPainter"
#include "QPen"
#include "QDebug"

class widgetForPainter: public QWidget
{
public:
    widgetForPainter();
    ~widgetForPainter() {;};
    QPen myPen;
    int x,y;


    private slots:
    void paintEvent(QPaintEvent *event);

public slots:
    void paintPoint(int x1,int y1);

};

#endif // WIDGETFORPAINTER_H

.cpp

#include "widgetforpainter.h"

widgetForPainter::widgetForPainter()
{
    //Pen
    myPen.setWidth(20);
    myPen.setColor(Qt::green);
    //myPen.setColor(QColor(255, 0, 0, 10));
    myPen.setCapStyle(Qt::RoundCap);
    myPen.setStyle(Qt::SolidLine);
}

void widgetForPainter::paintEvent(QPaintEvent *event)
{
    Q_UNUSED(event);
    QPainter myPainter; // Создаём объект отрисовщика
    myPainter.setPen(myPen);
    myPainter.drawPoint(x,y);
    myPainter.drawEllipse(x, y, x+50, x+50);
    qDebug()<<x<<y;
}

void widgetForPainter::paintPoint(int x1, int y1)
{
    QPainter myPainter; // Создаём объект отрисовщика
    myPainter.setPen(myPen);
    myPainter.drawPoint(x1,y1);
    myPainter.drawEllipse(x1, y1, x+50, x+50);
    qDebug()<<x1<<y1;
}

In the constructor of the main class did:

newGraphicsView =  new graphicsView();
    newGraphicsView->setScene(scene);    
    
    ui->verticalLayout->addWidget(newGraphicsView);


    widgetForPainter *myWidgetForPainter = new widgetForPainter();
    ui->verticalLayout->addWidget(myWidgetForPainter);

Probably in the paint void Scene::mousePressEvent(QGraphicsSceneMouseEvent *event) need to add widget For void Painter::paintPoint(int x1, int y1) but how to do it?

[Mikeeeeee]

This example works. Could you help me with the right code in my project.

[jsulm]

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

How to add x and y coordinates?

Come on, in the same way: override mousePressEvent as before.

[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".