Merge pull request #3718 from oslerw/master

Tweak captcha generation code

1 files changed, 22 insertions, 8 deletions

diff --git a/Duplicati/Server/WebServer/CaptchaUtil.cs b/Duplicati/Server/WebServer/CaptchaUtil.cs
index a7a56b5db..c7ac7e471 100644
--- a/Duplicati/Server/WebServer/CaptchaUtil.cs
+++ b/Duplicati/Server/WebServer/CaptchaUtil.cs
@@ -44,6 +44,17 @@ namespace Duplicati.Server.WebServer
                 .ToArray();

 

         /// <summary>

+        /// Approximate the size in pixels of text drawn at the given fontsize

+        /// </summary>

+        private static int ApproxTextWidth(string text, FontFamily fontfamily, int fontsize)

+        {

+            using (var font = new Font(fontfamily, fontsize, GraphicsUnit.Pixel))

+            using (var graphics = Graphics.FromImage(new Bitmap(1, 1))) {

+                return (int) graphics.MeasureString(text, font).Width;

+            }

+        }

+

+        /// <summary>

         /// Creates a random answer.

         /// </summary>

         /// <returns>The random answer.</returns>

@@ -67,20 +78,23 @@ namespace Duplicati.Server.WebServer
         /// <returns>The captcha image.</returns>

         /// <param name="answer">The captcha solution string.</param>

         /// <param name="size">The size of the image, omit to get a size based on the string.</param>

-        /// <param name="fontsize">The size of the font used to create the captcha.</param>

-        public static Bitmap CreateCaptcha(string answer, Size size = default(Size), int fontsize = 24)

+        /// <param name="fontsize">The size of the font used to create the captcha, in pixels.</param>

+        public static Bitmap CreateCaptcha(string answer, Size size = default(Size), int fontsize = 40)

         {

+            var fontfamily = FontFamily.GenericSansSerif;

+            var text_width = ApproxTextWidth(answer, fontfamily, fontsize);

             if (size.Width == 0 || size.Height == 0)

-                size = new Size((answer.Length + 1) * fontsize, fontsize * 2);

+                size = new Size((int) (text_width * 1.2), (int) (fontsize * 1.2));

 

             var bmp = new Bitmap(size.Width, size.Height);

             var rnd = new Random();

-            var stray_x = fontsize / 4;

+            var stray_x = fontsize / 2;

             var stray_y = size.Height / 4;

-

+            var ans_stray_x = fontsize / 3;

+            var ans_stray_y = size.Height / 6;

             using (var graphics = Graphics.FromImage(bmp))

-            using (var font1 = new Font("Ariel", fontsize))

-            using (var font2 = new Font("Ariel", fontsize))

+            using (var font1 = new Font(fontfamily, fontsize, GraphicsUnit.Pixel))

+            using (var font2 = new Font(fontfamily, fontsize, GraphicsUnit.Pixel))

             using (var font3 = new HatchBrush(HatchStyle.Shingle, Color.GhostWhite, Color.DarkBlue))

             {

                 graphics.Clear(Color.White);

@@ -106,7 +120,7 @@ namespace Duplicati.Server.WebServer
                         graphics.DrawLine(pen, rnd.Next(0, stray_x), i + rnd.Next(-stray_y, stray_y), size.Width - rnd.Next(0, stray_x), i + rnd.Next(-stray_y, stray_y));

 

                 // Draw the actual answer

-                graphics.DrawString(answer, font1, font3, ((size.Width - (fontsize * answer.Length)) / 2) + rnd.Next(-stray_x, stray_x), ((size.Height - (fontsize * 2)) / 2) + rnd.Next(-stray_y, stray_y));

+                graphics.DrawString(answer, font1, font3, ((size.Width - text_width) / 2) + rnd.Next(-ans_stray_x, ans_stray_x), ((size.Height - fontsize) / 2) + rnd.Next(-ans_stray_y, ans_stray_y));

 

                 return bmp;

             }