【Qt】Qtでお絵描きアプリを作ってみた【C++】

Qtでお絵描きアプリを作ってみました。

内容は以下になります。

mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QPixmap>
#include <QMouseEvent>
#include <QPainter>

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();

protected:
    void mousePressEvent(QMouseEvent *event) override;
    void mouseMoveEvent(QMouseEvent *event) override;
    void paintEvent(QPaintEvent *event) override;

private:
    QPixmap canvas;
    QPoint lastPoint;
    bool drawing;
};

#endif // MAINWINDOW_H

mainwindow.cpp

#include "mainwindow.h"

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent), drawing(false)
{
    resize(800, 600);
    canvas = QPixmap(size());
    canvas.fill(Qt::white);
}

MainWindow::~MainWindow()
{
}

void MainWindow::mousePressEvent(QMouseEvent *event)
{
    if (event->button() == Qt::LeftButton) {
        drawing = true;
        lastPoint = event->pos();
    }
}

void MainWindow::mouseMoveEvent(QMouseEvent *event)
{
    if (drawing && (event->buttons() & Qt::LeftButton)) {
        QPainter painter(&canvas);
        painter.setPen(QPen(Qt::black, 2, Qt::SolidLine, Qt::RoundCap));
        painter.drawLine(lastPoint, event->pos());
        lastPoint = event->pos();
        update(); // paintEventを呼び出す
    }
}

void MainWindow::paintEvent(QPaintEvent *event)
{
    QPainter painter(this);
    painter.drawPixmap(0, 0, canvas);
}

こんな感じになります。

↓↓↓youtube
https://youtu.be/NhBdVDPiexs