Svg image preview is displayed unscaled and uncentered (#8996)

* Fixed screen centering and scaling problem with SVG files

* Little shorter code.

* Improved exception caching

* typo

* fixed upscaling problem

* add CSS that IE6 can support it

* typo

* adding in spelling

Co-authored-by: Clint Rutkas <clint@rutkas.com>

.github/actions/spell-check/expect.txt

@@ -2335,6 +2335,8 @@ vk
 VKey
 VKTAB
 vm
+vmax
+vmin
 Voicemail
 VOS
 VREDRAW
@@ -2348,6 +2350,7 @@ VSTS
 VSTT
 VTABLE
 Vtbl
+vw
 Vx
 watsonportal
 wav
@@ -2480,6 +2483,7 @@ xa
 xamarin
 xaml
 XAngle
+XAttribute
 xbf
 XBind
 XBUTTON

src/modules/previewpane/SvgPreviewHandler/SvgPreviewControl.cs

@@ -65,6 +65,18 @@ public override void DoPreview<T>(T dataSource)
                 return;
             }
 
+            try
+            {
+                svgData = SvgPreviewHandlerHelper.AddStyleSVG(svgData);
+            }
+#pragma warning disable CA1031 // Do not catch general exception types
+            catch (Exception ex)
+#pragma warning restore CA1031 // Do not catch general exception types
+            {
+                _browser.ScrollBarsEnabled = true;
+                PowerToysTelemetry.Log.WriteEvent(new SvgFilePreviewError { Message = ex.Message });
+            }
+
             InvokeOnControlThread(() =>
             {
                 try
@@ -127,7 +139,7 @@ private void AddBrowserControl(string svgData)
             _browser.Dock = DockStyle.Fill;
             _browser.IsWebBrowserContextMenuEnabled = false;
             _browser.ScriptErrorsSuppressed = true;
-            _browser.ScrollBarsEnabled = true;
+            _browser.ScrollBarsEnabled = false;
             _browser.AllowNavigation = false;
             Controls.Add(_browser);
         }

src/modules/previewpane/SvgPreviewHandler/Utilities/SvgPreviewHandlerHelper.cs

@@ -68,5 +68,100 @@ public static bool CheckBlockedElements(string svgData)
 
             return foundBlockedElement;
         }
+
+        /// <summary>
+        /// Add proper
+        /// </summary>
+        /// <param name="stringSvgData">Input Svg</param>
+        /// <returns>Returns modified svgData with added style</returns>
+        public static string AddStyleSVG(string stringSvgData)
+        {
+            XElement svgData = XElement.Parse(stringSvgData);
+
+            var attributes = svgData.Attributes();
+            string width = string.Empty;
+            string height = string.Empty;
+            string widthR = string.Empty;
+            string heightR = string.Empty;
+            string oldStyle = string.Empty;
+
+            // Get width and height of element and remove it afterwards because it will be added inside style attribute
+            for (int i = 0; i < attributes.Count(); i++)
+            {
+                if (attributes.ElementAt(i).Name == "height")
+                {
+                    height = attributes.ElementAt(i).Value;
+                    attributes.ElementAt(i).Remove();
+                    i--;
+                }
+                else if (attributes.ElementAt(i).Name == "width")
+                {
+                    width = attributes.ElementAt(i).Value;
+                    attributes.ElementAt(i).Remove();
+                    i--;
+                }
+                else if (attributes.ElementAt(i).Name == "style")
+                {
+                    oldStyle = attributes.ElementAt(i).Value;
+                    attributes.ElementAt(i).Remove();
+                    i--;
+                }
+            }
+
+            svgData.ReplaceAttributes(attributes);
+
+            height = CheckUnit(height);
+            width = CheckUnit(width);
+            heightR = RemoveUnit(height);
+            widthR = RemoveUnit(width);
+
+            string centering = "position: absolute; top: 50%; left: 50%; transform: translate(-50%, -50%);";
+
+            // Because WebBrowser class is based on IE version that do not support max-width and max-height extra CSS is needed for it to work.
+            string scaling = $"max-width: {width} ; max-height: {height} ;";
+            scaling += $"  _height:expression(this.scrollHeight > {heightR} ? \" {height}\" : \"auto\"); _width:expression(this.scrollWidth > {widthR} ? \"{width}\" : \"auto\");";
+
+            svgData.Add(new XAttribute("style", scaling + centering + oldStyle));
+            return svgData.ToString();
+        }
+
+        /// <summary>
+        /// If there is a CSS unit at the end return the same string, else return the string with a px unit at the end
+        /// </summary>
+        /// <param name="length">CSS length</param>
+        /// <returns>Returns modified length</returns>
+        private static string CheckUnit(string length)
+        {
+            string[] cssUnits = { "cm", "mm", "in", "px", "pt", "pc", "em", "ex", "ch", "rem", "vw", "vh", "vmin", "vmax", "%" };
+            foreach (var unit in cssUnits)
+            {
+                if (length.EndsWith(unit, System.StringComparison.CurrentCultureIgnoreCase))
+                {
+                    return length;
+                }
+            }
+
+            return length + "px";
+        }
+
+        /// <summary>
+        /// Remove a CSS unit from the end of the string
+        /// </summary>
+        /// <param name="length">CSS length</param>
+        /// <returns>Returns modified length</returns>
+        private static string RemoveUnit(string length)
+        {
+            string[] cssUnits = { "cm", "mm", "in", "px", "pt", "pc", "em", "ex", "ch", "rem", "vw", "vh", "vmin", "vmax", "%" };
+            foreach (var unit in cssUnits)
+            {
+                if (length.EndsWith(unit, System.StringComparison.CurrentCultureIgnoreCase))
+                {
+                    length = length.Remove(length.Length - unit.Length);
+                    return length;
+                }
+            }
+
+            return length;
+        }
     }
 }