[Qt] Example of QPainter to create a simulator for led panels

LedPanel.hpp

#ifndef LEDPANEL_HPP
#define LEDPANEL_HPP
 
#include <QWidget>
 
#include <cassert>
#include <QPainter>
 
class LedPanel : public QWidget
{
    Q_OBJECT
 
public:
    LedPanel(QWidget *parent = 0)
        : QWidget(parent)
    {
        for (int x = 0; x < 32; ++x)
        {
            for (int y = 0; y < 8; ++y)
            {
                states[y][x] = false;
            }
        }
    }
 
    void on(unsigned int x, unsigned int y)
    {
        assert(x < 32);
        assert(y < 8);
        states[y][x] = true;
    }
 
protected:
    void paintEvent(QPaintEvent*) override
    {
        QPainter painter(this);
 
        // Background
        QBrush background(QColor(23, 23, 34));
        painter.setBrush(background);
        painter.drawRect(0, 0, width(), height());
 
        // LED
        int w = width() / 32;
        int h = height() / 8;
 
        for (int x = 0; x < 32; ++x)
        {
            for (int y = 0; y < 8; ++y)
            {
                if (states[y][x])
                {
                    QBrush led(QColor(0, 125, 110));
                    painter.setBrush(led);
                    QRect rect(x*w, y*h, w, h);
                    painter.drawRect(rect);
                }
            }
        }
    }
 
private:
    bool states[8][32]; // 8 lines of 32 LEDs each
};
 
#endif // LEDPANEL_HPP