Qt c++ QPainter QVector with QPoint - c++

Question

I have QVector<QPoint> m_vertices; in my drawingwidget.h
class DrawingWidget: public QWidget {
Q_OBJECT
public:
DrawingWidget(MainWindow *parent = 0);
~DrawingWidget();
QVector<QPoint> m_vertices;
I trying to implement adding/deleting vertices on my mainwindow. I managed to make the add function, now it's should be easy to delete them, but i am a bit confused.
The main idea is, that i have a pop-up menu, where i can choose a "tool". I can add vertex, remove vertex, move vertex, add line, delete line. The idea is , when i choose for example "Add Vertex" then the "m_state" will change to "ADD_VERTEX_SELECTED" so i can only add vertices and nothing else.
enum DrawingWidgetState {
NO_TOOL_SELECTED,
ADD_VERTEX_SELECTED,
MOVE_VERTEX_SELECTED,
DELETE_VERTEX_SELECTED,
ADD_LINE_SELECTED,
DELETE_LINE_SELECTED
};
Drawing
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);
}
MousePress event. On left click, I have to delete the vertex that I clicked on
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 == DELETE_VERTEX_SELECTED) {
if(event->button() == Qt::LeftButton) {
m_vertices.clear();
}
}
}
How can i do that ?

Answer 1

This code uses std::find_if together with a lambda expression to find the closest point. You probably want to allow a bit more leeway than the exact circle radius, but that is up to you.
auto it = std::find_if(m_vertices.begin(), m_vertices.end(), [point = event->pos](QPoint v) {
auto d = v - point;
return QPoint::dotProduct(d, d) < 400; // dotProduct returns square of distance
});
if (it != m_vertices.end()) {
m_vertices.erase(it);
}