C#でランダムな図形を描画した画像ファイルを作るプログラム

using System.Diagnostics;
using System.IO;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Shapes;

class Program
{
    static void CreateRandomImage(string bmpPath, int width=3840, int height=2160)
    {
        var canvas = new Canvas();
        canvas.Width = width;
        canvas.Height = height;
        canvas.Background = new SolidColorBrush(Colors.White);

        Random rnd = new(); // Randomオブジェクトを作成
        int stroke = (width < 1280) ? 1 : width / 1280;
        int max = (width < 7) ? 512 : width / 7;
        int min = (width < 30) ? 128 : width / 30;

        for(int i = 0; i < 1024; i++)
        {
            // 四角形
            Rectangle rectangle = new();
            
            rectangle.Width = rnd.Next(min, max);
            rectangle.Height= rnd.Next(min, max);
            SolidColorBrush mySolidColorBrush = new ();
            mySolidColorBrush.Color = Color.FromArgb(
                (byte)rnd.Next(0,255), (byte)rnd.Next(0,255), (byte)rnd.Next(0,255), 127);
            rectangle.Fill = mySolidColorBrush;

            rectangle.Stroke = new SolidColorBrush(Colors.Black);
            rectangle.StrokeThickness = stroke;

            canvas.Children.Add(rectangle);
            Canvas.SetLeft(rectangle, rnd.Next(1, (int)canvas.Width));
            Canvas.SetTop(rectangle, rnd.Next(1, (int)canvas.Width));

            // 多角形（三角形）
            Polyline polyline = new();
            
            polyline.Stroke = new SolidColorBrush(Colors.Black);
            polyline.StrokeThickness = stroke;
            polyline.FillRule = FillRule.EvenOdd;

            Point point1 = new(rnd.Next(min, max), rnd.Next(min, max));
            Point point2 = new(rnd.Next(min, max), rnd.Next(min, max));
            Point point3 = new(rnd.Next(min, max), rnd.Next(min, max));

            PointCollection pointCollection = new();
            pointCollection.Add(point1);
            pointCollection.Add(point2);
            pointCollection.Add(point3);

            polyline.Points = pointCollection;

            SolidColorBrush mySolidColorBrush2 = new ();
            mySolidColorBrush2.Color = Color.FromArgb(
                (byte)rnd.Next(0,255), (byte)rnd.Next(0,255), (byte)rnd.Next(0,255), 127);
            polyline.Fill = mySolidColorBrush2;

            canvas.Children.Add(polyline);
            Canvas.SetLeft(polyline, rnd.Next(1, (int)canvas.Width));
            Canvas.SetTop(polyline, rnd.Next(1, (int)canvas.Width));

            // 楕円
            Ellipse ellipse = new();
            ellipse.Stroke = new SolidColorBrush(Colors.Black);
            ellipse.StrokeThickness = stroke;
            SolidColorBrush mySolidColorBrush3 = new ();
            mySolidColorBrush3.Color = Color.FromArgb(
                (byte)rnd.Next(0,255), (byte)rnd.Next(0,255), (byte)rnd.Next(0,255), 127);
            ellipse.Fill = mySolidColorBrush3;
            ellipse.Width = rnd.Next(min, max);
            ellipse.Height = rnd.Next(min, max);

            canvas.Children.Add(ellipse);
            Canvas.SetLeft(ellipse, rnd.Next(1, (int)canvas.Width));
            Canvas.SetTop(ellipse, rnd.Next(1, (int)canvas.Width));

        }

        var size = new Size(canvas.Width, canvas.Height);
        canvas.Measure(size);
        canvas.Arrange(new Rect(size));

        var renderBitmap = new RenderTargetBitmap(
        (int)size.Width, 
        (int)size.Height, 
        96, 96, PixelFormats.Pbgra32);
        renderBitmap.Render(canvas);

        System.Windows.Media.Imaging.BitmapEncoder encoder;

        using (var fs = new FileStream(bmpPath, FileMode.Create))
        {
            string ext = System.IO.Path.GetExtension(bmpPath).ToUpper();

            if (ext == ".BMP")
            {
                encoder = new BmpBitmapEncoder();
            }
            else if (ext == ".JPG")
            {
                encoder = new JpegBitmapEncoder();
            }
            else if (ext == ".PNG")
            {
                encoder = new PngBitmapEncoder();
            }
            else
            {
                throw new FileFormatException(bmpPath);
            }

            encoder.Frames.Add(BitmapFrame.Create(renderBitmap));
            encoder.Save(fs);
        }
    }
    [STAThread]
    public static void Main()
    {
        const string imgPath = @"./sample.png";
        const int width = 1280;
        const int height = 720;
        CreateRandomImage(imgPath, width, height);
    }
}