Qt C++ QLine QPoint - c++

Question

I have QVector<QPoint> m_vertices and QVector<QLine> in my drawingWidget.h
I currently trying to do a simple drawing tool, where I can add vertices and lines. I managed to draw multiple vertices on my "MainWindow", but I can't really understand, how can I implement a line between created vertices.
Basically I have two points created and by pressing the left mouse button on the first vertex and left mouse button on the second vertex... it's should create a line between them.
How can I do that?
void DrawingWidget::paintEvent(QPaintEvent *event) {
QPainter painter(this);
painter.fillRect(event->rect(), Qt::blue);
painter.setBrush(Qt::black);
for(int i = 0; i < m_vertices.size() ; i++) {
painter.drawEllipse(m_vertices[i], 20, 20);
}
}
void DrawingWidget::mousePressEvent(QMouseEvent *event) {
if(m_state == ADD_VERTEX_SELECTED) {
if(event->button() == Qt::LeftButton) {
//m_x = event->x();
//m_y = event->y();
//update();
QPoint point = event->pos();
m_vertices.append(point);
update();
}
}
if(m_state == ADD_LINE_SELECTED) {
if(event->button() == Qt::LeftButton) {
QPoint Startpoint = event->x();
QPoint Endpoint = event->y();
}
}
}

Answer 1

You are almost there. You need to use QPainter::drawLine for this and pass the two consecutive mouse QPoints from m_vertices.
For example
void DrawingWidget::paintEvent(QPaintEvent *event)
{
QPainter painter(this);
painter.fillRect(event->rect(), Qt::blue);
painter.setPen(QPen(Qt::black, 3)); // width of the line
if(m_vertices.size() == 1) // for the first mouse click
painter.drawEllipse(m_vertices[0], 4, 4);
for(int i = 0; i < m_vertices.size()-1 ; i++)
{
const QPoint& point1 = m_vertices[i];
const QPoint& point2 = m_vertices[i+1];
// draw the mouse point
painter.drawEllipse(point1, 4, 4);
painter.drawEllipse(point2, 4, 4);
// draw the line
painter.drawLine(point1, point2);
}
}