QPaint - Saving coordinates of 2 mouse clicks and the drawing line between them

Good Day,

//I'm fairly proficient in qt -> got some problems with interactive programming as:

1) I created a simple label
2) Uploaded Image to Label
3) using mouseEvents & paintEvent was able to create point on Image
4) MY PROBLEM: the 2nd mouse click! //& store 2nd point where?

User needs to click twice to get 2 points(line will be drawn between them, however everytime in the running program! when I click for a second time, the initial point becomes the new point.

some att code:
void label::mousePressEvent(QMouseEvent *event)
{
paintFlag = 0;
if(event->button()==Qt::LeftButton)
{
this->x = ev->x();
this->y = ev->y();
//store 1st point
x1 = x;
y1 = y;
emit Mouse_Pressed();
paintFlag = 1;

//Mouse Pressed Again! 2nd point
x2 = x;
y2 = y;
emit Mouse_Pressed();
}

}

paintEvent:
QPainter painter(this);
QPen paintpen(Qt::red);
paintpen.setWidth(4);

QPoint p1;
p1.setX(x1);
p1.setY(y1);

painter.setPen(paintpen);
painter.drawPoint(p1);

}


Any ideas on my problem... what am i not seeing!
Thanks

Code:

---

void label::mousePressEvent(QMouseEvent *event)
{
    paintFlag = 0;
    if(event->button()==Qt::LeftButton)
    {
        this->x = ev->x();
        this->y = ev->y();
 
        //store 1st point
        if(firstClick) // set firstClick = true; in ctor
        {
            x1 = x;
            y1 = y;
            emit Mouse_Pressed();
            firstClick = false;
        }
        paintFlag = 1;
 
        //Mouse Pressed Again! 2nd point
        if(!firstClick) //EDIT: corrected
        {
            x2 = x;
            y2 = y;
            emit Mouse_Pressed();
            firstClick = true;
        }
    }
}

---

Thanks for the quick response, however as I implemented that
as the program begins it automatically creates a point at (0, 0) and a point following my mouse pointer -> moving line as mouse hovers around... its cool but not what i want it to do... new problem derived from prev1.

attached my drawFunc:

Code:

---

void my_qlabel::paintEvent(QPaintEvent *e)
{
    if(paintFlag == 1)
    {
    QPainter painter(this);
    QPen paintpen(Qt::red);
    paintpen.setWidth(4);
 
    QPen linepen(Qt::black);
    linepen.setWidth(4);
 
    QPoint p1;
    p1.setX(x);
    p1.setY(y);
 
 
    QPoint p2;
    p2.setX(x2);
    p2.setY(y2);
 
    painter.setPen(linepen);
    painter.drawLine(p1, p2);
 
    painter.setPen(paintpen);
    painter.drawPoint(p1);
 
    painter.setPen(paintpen);
    painter.drawPoint(p2);
 
    //paintFlag = 2;
 
    }
    update();
}

---

Also note: the paintEvent starts immediately hence i put a flagCounter to initiate it ?

Kind Regards

Post the complete code again

Code:

---

void my_qlabel::mousePressEvent(QMouseEvent *ev)
{
    paintFlag = 0;
    if(ev->button()==Qt::LeftButton)
    {
        this->x = ev->x();
        this->y = ev->y();
 
        //store 1st point
        if(firstClick)
        {
            this->x = ev->x();
            this->y = ev->y();
            x1 = x;
            y1 = y;
            emit Mouse_Pressed();
            firstClick = false;
        }
 
        //Mouse Pressed Again! 2nd point
        if(firstClick)
        {
              x2 = x;
              y2 = y;
              emit Mouse_Pressed();
              firstClick = true;
        }
 
        paintFlag = 1;
 
       //calculateAngle(x, y, x1, y2);
    }
}

---

paint event:

Code:

---

void my_qlabel::paintEvent(QPaintEvent *e)
{
    if(paintFlag == 1)
    {
    QPainter painter(this);
    QPen paintpen(Qt::red);
    paintpen.setWidth(4);
 
    QPen linepen(Qt::black);
    linepen.setWidth(4);
 
    QPoint p1;
    p1.setX(x1);
    p1.setY(y1);
 
    painter.setPen(paintpen);
    painter.drawPoint(p1);
 
    QPoint p2;
    p2.setX(x2);
    p2.setY(y2);
 
    painter.setPen(paintpen);
    painter.drawPoint(p2);
 
    painter.setPen(linepen);
    painter.drawLine(p1, p2);
 
    }
    update();
}

---

It starts from point(0, 0) instead of where user clicks
when user does click it creates an end point & a line from the (0, 0)

Goal: user must click start point, click end point, line to be drawn between 2 points, and points must be saved for later calculations

I know moreOrLess how to do it, just cant seem to get my head around this mouse clicking

Kind Regards

Try this correction

Code:

---

void my_qlabel::mousePressEvent(QMouseEvent *ev)
{
    paintFlag = 0;
    if(ev->button()==Qt::LeftButton)
    {
        this->x = ev->x();
        this->y = ev->y();
 
        //store 1st point
        if(firstClick)
        {
            this->x = ev->x();
            this->y = ev->y();
            x1 = x;
            y1 = y;
            emit Mouse_Pressed();
            firstClick = false;
        }
 
        //Mouse Pressed Again! 2nd point
        if(!firstClick)
        {
              x2 = x;
              y2 = y;
              emit Mouse_Pressed();
              firstClick = true;
              paintFlag = 1;
        }
    }
}

---

Tried it -> unfortunately Back to square 1 :)
creates a single point wherever the user clicks... User needs to click twice to get 2 points(line will be drawn between them, however every time in the running program! when I click for a second time, the initial point becomes the new point.) no line shown

this twist in the tail got me stranded

any other ideas?

Code:

---

#include <QtGui>
#include <QtWidgets>
#include <QApplication>
 
class Label : public QLabel
{
public:
    explicit Label(QWidget * parent = 0)
        : QLabel(parent)
        , mStartX(0)
        , mStartY(0)
        , mEndX(0)
        , mEndY(0)
        , mFirstClick(true)
        , mPaintFlag(false)
    {
        ;
    }
 
protected:
    void mousePressEvent(QMouseEvent * e)
    {
        if(e->button() == Qt::LeftButton)
        {
            //store 1st point
            if(mFirstClick)
            {
                mStartX = e->x();
                mStartY = e->y();
                mFirstClick = false;
            }
            //Mouse Pressed Again! 2nd point
            else if(!mFirstClick)
            {
                mEndX = e->x();
                mEndY = e->y();
                mFirstClick = true;
                mPaintFlag = true;
                update();
            }
        }
    }
 
    void paintEvent(QPaintEvent * e)
    {
        QLabel::paintEvent(e);
 
        if(mPaintFlag)
        {
            QPainter painter(this);
            QPen paintpen(Qt::red);
            paintpen.setWidth(4);
 
            QPen linepen(Qt::black);
            linepen.setWidth(4);
 
            QPoint p1;
            p1.setX(mStartX);
            p1.setY(mStartY);
 
            painter.setPen(paintpen);
            painter.drawPoint(p1);
 
            QPoint p2;
            p2.setX(mEndX);
            p2.setY(mEndY);
 
            painter.setPen(paintpen);
            painter.drawPoint(p2);
 
            painter.setPen(linepen);
            painter.drawLine(p1, p2);
        }
    }
 
private:
    int mStartX;
    int mStartY;
    int mEndX;
    int mEndY;
 
    bool mFirstClick;
    bool mPaintFlag;
};
 
int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
 
    Label w;
    w.show();
 
    return app.exec();
}

---

Thanks Santosh

Highly appreciated:)

I Might have future queries on future logical & syntax bugs
Will add you in future post.

Kind Regards

Good Day,

Once again I find myself in a stumbling block! :confused:

Once above program created - It saves 2 points and draws line between them.
New Issue:
1) if my Paint Event Name is as above "void mmetLabel::paintEvent(QPaintEvent *ev)"
i'm able to draw line between 2 points and displayed. however i'm unable to load image.

2) however if I change Paint Event Name as "void mmetLabel::drawSometing(QPaintEvent *ev)"
then my picture upload function works (Pic Displayed), 2 points are saved... BUT points and lines not displayed

Any Ideas?

Call the base paintEvent.

Code:

---

void mmetLabel::paintEvent(QPaintEvent *ev)
{
    QLabel::paintEvent(ev); //<<<<<<<<< Add this as first line
...
}

---

Works like a dream!
Thanks, Santosh.

Any good Books you know that will make me more proficient in qt

Thanks again

IMO Books provide you with content and may be examples, one becomes provicient by practice.

Anyway refer this Post

Kind Regards