Fix decimal separator using invariant culture

src/ACadSharp.Pdf.Tests/PdfExporterTests.cs

@@ -1,5 +1,9 @@
+using ACadSharp.Entities;
 using ACadSharp.IO;
+using CSMath;
+using System.Globalization;
 using System.IO;
+using System.Text;
 using Xunit;
 using Xunit.Abstractions;
 
@@ -55,6 +59,42 @@ public void AddModelSpaceTest()
 			exporter.Close();
 		}
 
+		[Fact]
+		public void InvariantDecimalSeparatorTest()
+		{
+			CultureInfo previousCulture = CultureInfo.CurrentCulture;
+
+			try
+			{
+				//A culture such as fr-FR uses the comma as decimal separator,
+				//which would produce an invalid pdf stream if numbers were not
+				//formatted using the invariant culture.
+				CultureInfo.CurrentCulture = new CultureInfo("fr-FR");
+
+				CadDocument doc = new CadDocument();
+				doc.Entities.Add(new Line(new XYZ(0, 0, 0), new XYZ(12.5, 7.25, 0)));
+
+				string content;
+				using (MemoryStream stream = new MemoryStream())
+				{
+					PdfExporter exporter = new PdfExporter(stream);
+					exporter.AddModelSpace(doc);
+					exporter.Close();
+
+					content = Encoding.ASCII.GetString(stream.ToArray());
+				}
+
+				//No number must use the comma as decimal separator.
+				Assert.DoesNotMatch(@"\d,\d", content);
+				//The decimal point must be used (e.g. MediaBox, coordinates).
+				Assert.Contains(".", content);
+			}
+			finally
+			{
+				CultureInfo.CurrentCulture = previousCulture;
+			}
+		}
+
 		[Theory]
 		[MemberData(nameof(LayoutNames))]
 		public void WriteLayouts(string name)

src/ACadSharp.Pdf/Core/IO/PdfPen.cs

@@ -7,6 +7,7 @@
 using CSMath;
 using System;
 using System.Collections.Generic;
+using System.Globalization;
 using System.Linq;
 using System.Text;
 
@@ -123,7 +124,7 @@ private void applyStyle(Entity entity)
 		{
 			LineWeightType lw = entity.GetActiveLineWeightType();
 			double lwValue = lw.GetLineWeightValue();
-			this._sb.AppendLine($"{lwValue.ToPdfUnit(PdfUnitType.Millimeter)} {PdfKey.LineWidth}");
+			this._sb.AppendLine($"{lwValue.ToPdfUnit(PdfUnitType.Millimeter).ToString(this._configuration.DecimalFormat, CultureInfo.InvariantCulture)} {PdfKey.LineWidth}");
 
 			Color color = entity.GetActiveColor();
 
@@ -322,7 +323,7 @@ private void drawViewport(Viewport viewport)
 
 		private string toPdfDouble(double value)
 		{
-			return (value / this.DenominatorScale).ToPdfUnit(this.PaperUnits).ToString(this._configuration.DecimalFormat);
+			return (value / this.DenominatorScale).ToPdfUnit(this.PaperUnits).ToString(this._configuration.DecimalFormat, CultureInfo.InvariantCulture);
 		}
 
 		private void writeEntityEnd(Entity entity)

src/ACadSharp.Pdf/Core/PdfReference.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Globalization;
 
 namespace ACadSharp.Pdf.Core
 {
@@ -20,7 +21,14 @@ public void Print()
 
 		public override string GetPdfForm(PdfConfiguration configuration)
 		{
-			return this._f.Invoke().ToString();
+			T value = this._f.Invoke();
+
+			if (value is IFormattable formattable)
+			{
+				return formattable.ToString(null, CultureInfo.InvariantCulture);
+			}
+
+			return value.ToString();
 		}
 	}
 }

src/ACadSharp.Pdf/Extensions/XYZExtensions.cs

@@ -2,6 +2,7 @@
 using ACadSharp.Pdf.Core;
 using CSMath;
 using System;
+using System.Globalization;
 
 namespace ACadSharp.Pdf.Extensions
 {
@@ -39,7 +40,7 @@ public static class ColorExtensions
 	{
 		public static string ToPdfString(this Color color)
 		{
-			return $"{color.R / 255d} {color.G / 255d} {color.B / 255d} RG";
+			return string.Format(CultureInfo.InvariantCulture, "{0} {1} {2} RG", color.R / 255d, color.G / 255d, color.B / 255d);
 		}
 	}
 }