/// <summary>
/// Generate a new captcha.
/// </summary>
/// <param name="cancellationToken"></param>
/// <returns>The captcha.</returns>
public async ValueTask <ICaptcha <Bitmap> > GenerateNewAsync(CancellationToken cancellationToken = default)
{
if (this.IsDisposed)
{
throw new ObjectDisposedException(null);
}
var random = RandomValueGenerator.GetRandom();
return(await Task.Run(async() =>
{
string resultString;
{
var length = this.lengths[random.Next(this.lengths.Length)];
StringBuilder builder = new StringBuilder(length);
for (int i = 0; i < length; i++)
{
builder.Append(this.characters[random.Next(this.characters.Length)]);
}
resultString = builder.ToString();
}
Bitmap image = new Bitmap(resultString.Length * 16, 27);
using Graphics g = Graphics.FromImage(image);
g.Clear(Color.White);
using var silverPen = new Pen(Color.Silver);
for (int i = 0; i < 25; i++)
{
int x1 = random.Next(image.Width);
int x2 = random.Next(image.Width);
int y1 = random.Next(image.Height);
int y2 = random.Next(image.Height);
g.DrawLine(silverPen, x1, x2, y1, y2);
}
using LinearGradientBrush brush = new LinearGradientBrush(
new Rectangle(0, 0, image.Width, image.Height), Color.Blue, Color.DarkRed, 1.2f, true);
g.DrawString(resultString, this.fonts[random.Next(this.fonts.Length)], brush, 3, 2);
for (int i = 0; i < 100; i++)
{
int x = random.Next(image.Width);
int y = random.Next(image.Height);
image.SetPixel(x, y, Color.FromArgb(random.Next()));
}
g.DrawRectangle(silverPen, 0, 0, image.Width - 1, image.Height - 1);
var id = await this.SaveAnswerAsync(resultString, cancellationToken).ConfigureAwait(false);
return new Captcha()
{
Display = image,
Id = id
};
}, cancellationToken).ConfigureAwait(false));
}