画面上のQRコードを読み取るWindowsアプリの作成

🎯 背景

Windowsで画面に表示されているQRコードを読み取りたいとき、
ちょうどいいアプリが見つからなかったので自作しました。
ひとまず動きました。
作成にはAI生成を利用しています。

🧩 できること

• 画面の任意範囲を選択
• QRコードを読み取り
• テキストとして取得＆コピー

🛠️ 使用技術

• .NET 10
• WPF
• ZXing.Net
• ZXing.Net.Bindings.Windows.Compatibility

メイン画面

メイン画面です。ひとまず動かしたかっただけなので、雑です。

MainWindow.xaml

<Window x:Class="ScreenQRCodeReader.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:ScreenQRCodeReader"
        mc:Ignorable="d"
        Title="MainWindow" Height="400" Width="250">
    <Grid>
        <StackPanel Margin="10">
            <Button Content="QRコード取得" Height="40" Click="Capture_Click"/>
            <Image x:Name="DebugImage"
       Height="120"
       Stretch="Uniform"
       Margin="0,10"/>
            <TextBox x:Name="ResultText"
                 Margin="0,10,0,10"
                 Height="60"
                 TextWrapping="Wrap"
                 AcceptsReturn="True"/>
            <Button Content="コピー" Height="40" Click="Copy_Click"/>
        </StackPanel>
    </Grid>
</Window>

MainWindow.xaml.cs

using System.Drawing;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using ZXing.Windows.Compatibility;

namespace ScreenQRCodeReader
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        private void Capture_Click(object sender, RoutedEventArgs e)
        {
            this.Hide();

            try
            {
                var selector = new SelectionWindow();
                if (selector.ShowDialog() == true)
                {
                    string? text = null;
                    var bmp = CaptureArea(selector.X, selector.Y, selector.W, selector.H);

                    try
                    {
                        // デバッグ表示
                        this.DebugImage.Source = BitmapUtil.ConvertBitmap(bmp);
                        // QR解析
                        text = DecodeQR(bmp);
                    }
                    finally
                    {
                        bmp.Dispose();
                    }

                    ResultText.Text = text ?? "QRコードが見つかりません";
                }
            }
            finally
            {
                this.Show();
            }
        }

        private string? DecodeQR(Bitmap bitmap)
        {
            var reader = new BarcodeReader();
            var result = reader.Decode(bitmap);
            return result?.Text;
        }

        private Bitmap CaptureArea(int x, int y, int width, int height)
        {
            var bmp = new Bitmap(width, height);

            using (var g = Graphics.FromImage(bmp))
            {
                g.CopyFromScreen(x, y, 0, 0, new System.Drawing.Size(width, height));
            }

            return bmp;
        }

        private void Copy_Click(object sender, RoutedEventArgs e)
        {
            if (!string.IsNullOrEmpty(ResultText.Text))
            {
                System.Windows.Clipboard.SetText(ResultText.Text);
            }
        }
    }
}

キャプチャ用画面

SelectionWindow.xaml

<Window x:Class="ScreenQRCodeReader.SelectionWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:ScreenQRCodeReader"
        mc:Ignorable="d"
        WindowStyle="None"
        AllowsTransparency="True"
        Background="#40000000"
        Topmost="True"
        WindowState="Maximized"
        Title="SelectionWindow">
    <Grid>
        <Canvas x:Name="RootCanvas">
			<TextBlock x:Name="CoordText"
               Foreground="White"
               Background="#80000000"
               FontSize="14"
               Padding="5"
               Visibility="Collapsed"/>
            <Rectangle x:Name="SelectionRect"
                   Stroke="Red"
                   StrokeThickness="2"
                   Fill="#40FFFFFF"
                   Visibility="Collapsed"/>
        </Canvas>
    </Grid>
</Window>

SelectionWindow.xaml.cs

using System;
using System.Drawing;
using System.Windows;
using System.Windows.Input;
using System.Windows.Shapes;
using System.Windows.Controls;

namespace ScreenQRCodeReader
{
    /// <summary>
    /// Interaction logic for SelectionWindow.xaml
    /// </summary>
    public partial class SelectionWindow : Window
    {
        private System.Windows.Point Start;
        private System.Windows.Shapes.Rectangle RangeRect;

        public int X { get; private set; }
        public int Y { get; private set; }
        public int W { get; private set; }
        public int H { get; private set; }

        public SelectionWindow()
        {
            InitializeComponent();
            RangeRect = SelectionRect;

            MouseDown += OnMouseDown;
            MouseMove += OnMouseMove;
            MouseUp += OnMouseUp;
            KeyDown += (_, e) => { if (e.Key == Key.Escape) Close(); };
        }

        private void OnMouseDown(object sender, MouseButtonEventArgs e)
        {
            Start = e.GetPosition(this);
            Canvas.SetLeft(RangeRect, Start.X);
            Canvas.SetTop(RangeRect, Start.Y);
            RangeRect.Width = 0;
            RangeRect.Height = 0;
            RangeRect.Visibility = Visibility.Visible;
        }

        private void OnMouseMove(object sender, System.Windows.Input.MouseEventArgs e)
        {
            var pos = e.GetPosition(this);

            var startScreen = this.PointToScreen(Start);
            var posScreen = this.PointToScreen(pos);

            // 座標表示（常に更新）
            CoordText.Text = $"X:{(int)posScreen.X}  Y:{(int)posScreen.Y}";
            Canvas.SetLeft(CoordText, pos.X);
            Canvas.SetTop(CoordText, pos.Y);
            CoordText.Visibility = Visibility.Visible;

            if (e.LeftButton == MouseButtonState.Pressed)
            {
                double x = Math.Min(pos.X, Start.X);
                double y = Math.Min(pos.Y, Start.Y);
                double w = Math.Abs(pos.X - Start.X);
                double h = Math.Abs(pos.Y - Start.Y);

                Canvas.SetLeft(RangeRect, x);
                Canvas.SetTop(RangeRect, y);
                RangeRect.Width = w;
                RangeRect.Height = h;

                // 範囲サイズも表示
                CoordText.Text += $"  W:{(int)w} H:{(int)h}";
            }
        }

        private void OnMouseUp(object sender, MouseButtonEventArgs e)
        {
            var end = e.GetPosition(this);

            var startScreen = this.PointToScreen(Start);
            var endScreen = this.PointToScreen(end);

            double x = Math.Min(startScreen.X, endScreen.X);
            double y = Math.Min(startScreen.Y, endScreen.Y);
            double w = Math.Abs(startScreen.X - endScreen.X);
            double h = Math.Abs(startScreen.Y - endScreen.Y);

            if (w < 1 || h < 1) { Close(); return; }

            this.X = (int)x;
            this.Y = (int)y;
            this.W = (int)w;
            this.H = (int)h;

            DialogResult = true;
            Close();
        }
    }
}

Bitmap操作

BitmapUtil.cs

using System;
using System.Windows.Media.Imaging;
using System.Runtime.InteropServices;
using System.Drawing;

namespace ScreenQRCodeReader
{
    internal class BitmapUtil
    {
        [DllImport("gdi32.dll")]
        public static extern bool DeleteObject(IntPtr hObject);

        public static BitmapSource ConvertBitmap(Bitmap bitmap)
        {
            IntPtr hBitmap = bitmap.GetHbitmap();

            try
            {
                return System.Windows.Interop.Imaging.CreateBitmapSourceFromHBitmap(
                    hBitmap,
                    IntPtr.Zero,
                    System.Windows.Int32Rect.Empty,
                    BitmapSizeOptions.FromEmptyOptions());
            }
            finally
            {
                DeleteObject(hBitmap); // メモリリーク防止
            }
        }
    }
}

工夫ポイント

• ウィンドウを一旦 Hide() して自分を写さない
• PointToScreen() で正確な座標取得

はまったところ

• 選択枠がキャプチャに写る問題
• DPIスケーリング
  → 環境によって座標ズレる可能性あり？

まとめ

• ZXing.Netはとても便利でした
• https://github.com/gippol/Win-AreaQR-Readerで公開しています