CODEWITHSUNDEEP
c++qt5qwidget
bunto1
bunto1

Reputation: 331

How to draw line behind buttons in Qt?

Question

In a custom widget, I'd like to draw lines (using QPainter) that connect buttons in a QGridLayout. The lines shall be behind the buttons, in order to

Considering ideas from this question, I could almost realize a simple, basic version running in my GUI application (source code below).

As long as I use QPushButton with the standard Qt style, it works like a charm (left), but, as I want to use a custom style, the lines overlap (right):

Qt style buttons Custom style buttons

What property or mechanism is causing this behavior?

Code

MyFrame.h:

#include <QFrame>

class MyFrame : public QFrame
{
public:
    MyFrame();
    virtual ~MyFrame() = default;
};

MyFrame.cpp:

#include "MyFrame.h"

#include "LineDrawWidget.h"

#include <QVBoxLayout>
#include <QGridLayout>
#include <QPushButton>
#include <QButtonGroup>

MyFrame::MyFrame()
{
    auto* mainLayout = new QVBoxLayout(this);
    auto* buttonLayout = new QGridLayout();

    QPushButton* button;
    auto* buttons = new QButtonGroup();
    for (int i = 0; i < 3; ++i) {
        button = new QPushButton();
        button->setText(QString::number(i+1));
        button->setFixedHeight(40);
        button->setFixedWidth(40);
        button->setStyleSheet("QPushButton { color : black; background-color : white; }");
        button->setStyleSheet("QPushButton { border-style : outset; border-color: black; border-width: 2px; border-radius: 6px; }");
        buttonLayout->addWidget(button);
        buttons->addButton(button, i);
    }

    auto* lineDraw = new LineDrawWidget(
            buttons->button(0),
            buttons->button(2));
    lineDraw->setLayout(buttonLayout);
    mainLayout->addWidget(lineDraw);
}

LineDrawWidget.h:

#include <QWidget>

class LineDrawWidget : public QWidget
{
public:
    LineDrawWidget(
            QWidget* from,
            QWidget* to,
            QWidget* parent = nullptr);
    virtual ~LineDrawWidget() = default;

protected:
    virtual void paintEvent(QPaintEvent* e) final override;

private:
    QWidget* _from;
    QWidget* _to;
};

LineDrawWidget.cpp:

#include "LineDrawWidget.h"

#include <QPainter>

LineDrawWidget::LineDrawWidget(
        QWidget* from,
        QWidget* to,
        QWidget* parent) :
        QWidget(parent),
        _from(from),
        _to(to)
{

}

void LineDrawWidget::paintEvent(QPaintEvent* e)
{
    (void)e;

    QPainter painter(this);

    QPoint start =  _from->mapToGlobal(_from->rect().bottomLeft());
    QPoint end = _to->mapToGlobal(_to->rect().topRight());
    painter.drawLine(mapFromGlobal(start), mapFromGlobal(end));
}

Upvotes: 0

Views: 940

Answers (1)

G.M.
G.M.

Reputation: 12899

I think the problem is the two separate calls to setStyle for a single QPushButton -- the second call appears to reset all properties not present in it. Try putting it all in a single call...

button->setStyleSheet("color : black; background-color : white; border-style : outset; border-color: black; border-width: 2px; border-radius: 6px;");

Seems to work for me.

Upvotes: 1

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