fix(svg): preserve point marker size during zoom

ACadSharp.Image.Tests/SvgExportTests.cs

@@ -46,7 +46,7 @@ public void RenderSvgProducesSvgPage()
     }
 
     [Fact]
-    public void PointRadiusIsConvertedFromPixelsIntoDrawingUnits()
+    public void ScalingPointRadiusIsConvertedFromPixelsIntoDrawingUnits()
     {
         BlockRecord block = new("points");
         block.Entities.Add(new Line(new XYZ(0, 0, 0), new XYZ(100, 50, 0)));
@@ -55,6 +55,7 @@ public void PointRadiusIsConvertedFromPixelsIntoDrawingUnits()
         exporter.Configuration.Width = 1000;
         exporter.Configuration.Height = 500;
         exporter.Configuration.SetPadding(0);
+        exporter.Configuration.Svg.NonScalingStroke = false;
         exporter.Add(block);
 
         using RenderedPage page = Assert.Single(exporter.Render(ImageExportFormat.Svg));
@@ -66,6 +67,32 @@ public void PointRadiusIsConvertedFromPixelsIntoDrawingUnits()
         Assert.Equal("0.2", (string?)circle.Attribute("r"));
     }
 
+    [Theory]
+    [InlineData(100)]
+    [InlineData(216101.36407904)]
+    public void NonScalingPointMarkerKeepsItsPixelDiameterIndependentOfDrawingExtents(double extent)
+    {
+        BlockRecord block = new("point-marker");
+        block.Entities.Add(new Line(new XYZ(0, 0, 0), new XYZ(extent, 100, 0)));
+        block.Entities.Add(new Point { Location = new XYZ(extent / 2, 50, 0) });
+        ImageExporter exporter = new();
+        exporter.Configuration.Width = 2000;
+        exporter.Configuration.Height = 2000;
+        exporter.Configuration.SetPadding(0);
+        exporter.Add(block);
+
+        using RenderedPage page = Assert.Single(exporter.Render(ImageExportFormat.Svg));
+        XElement marker = Assert.Single(XDocument.Parse(((RenderedSvgPage)page).Content).Descendants(),
+            element => element.Attribute("data-type")?.Value == "POINT");
+        Assert.Equal("line", marker.Name.LocalName);
+        Assert.Equal(marker.Attribute("x1")?.Value, marker.Attribute("x2")?.Value);
+        Assert.Equal(marker.Attribute("y1")?.Value, marker.Attribute("y2")?.Value);
+        Assert.Equal("4", marker.Attribute("stroke-width")?.Value);
+        Assert.Equal("round", marker.Attribute("stroke-linecap")?.Value);
+        Assert.Equal("none", marker.Attribute("stroke-dasharray")?.Value);
+        Assert.Equal("non-scaling-stroke", marker.Attribute("vector-effect")?.Value);
+    }
+
     [Fact]
     public void YAxisIsFlipped()
     {

ACadSharp.Image/Rendering/EntityRenderDispatcher.cs

@@ -256,7 +256,7 @@ private void DrawPoint(ImageRenderContext context, ImageStyle style, ACadSharp.E
     {
         // DotSizePixels is a pixel size; SVG surface units are drawing units, so it has to be converted.
         float radius = Math.Max(1f, this._configuration.DotSizePixels / 2f);
-        context.Surface.FillCircle(style, context.ToSurfacePoint(point.Location), context.ToSurfacePixels(radius));
+        context.Surface.DrawPointMarker(style, context.ToSurfacePoint(point.Location), context.ToSurfacePixels(radius), radius);
     }
 
     /// <summary>

ACadSharp.Image/Rendering/IDrawingSurface.cs

@@ -67,6 +67,16 @@ internal interface IDrawingSurface : IDisposable
 
     void FillCircle(ImageStyle style, SurfacePoint center, double radius);
 
+    /// <summary>
+    /// Draws a point marker, retaining its pixel size on interactive SVG surfaces.
+    /// </summary>
+    /// <param name="style">Marker colour and opacity.</param>
+    /// <param name="center">Marker centre in surface coordinates.</param>
+    /// <param name="radius">Radius in surface units for raster and scaling output.</param>
+    /// <param name="radiusPixels">Radius in display pixels for non-scaling output.</param>
+    void DrawPointMarker(ImageStyle style, SurfacePoint center, double radius, double radiusPixels)
+        => this.FillCircle(style, center, radius);
+
     void DrawText(ImageStyle style, SurfaceText text);
 
     /// <summary>

ACadSharp.Image/Rendering/Svg/SvgDrawingSurface.cs

@@ -371,6 +371,33 @@ public void FillCircle(ImageStyle style, SurfacePoint center, double radius)
             new XAttribute("cx", this.N(center.X)), new XAttribute("cy", this.N(center.Y)), new XAttribute("r", this.N(Math.Abs(radius)))), style));
     }
 
+    public void DrawPointMarker(ImageStyle style, SurfacePoint center, double radius, double radiusPixels)
+    {
+        if (!this._options.NonScalingStroke)
+        {
+            this.FillCircle(style, center, radius);
+            return;
+        }
+
+        if (!IsFinite(center) || !IsFinite(radiusPixels) || radiusPixels <= 0d)
+        {
+            this.NotifyNonFinite();
+            return;
+        }
+
+        // A zero-length round-capped stroke is a dot. Unlike a filled circle,
+        // its non-scaling stroke keeps the configured diameter during zoom.
+        ImageStyle markerStyle = style with { StrokeWidth = (float)(2d * radiusPixels), DashPattern = null };
+        XElement marker = new(Ns + "line",
+            new XAttribute("x1", this.N(center.X)), new XAttribute("y1", this.N(center.Y)),
+            new XAttribute("x2", this.N(center.X)), new XAttribute("y2", this.N(center.Y)),
+            new XAttribute("stroke-linecap", "round"));
+        marker = this.Stroked(marker, markerStyle);
+        marker.SetAttributeValue("stroke-width", this.S(markerStyle.StrokeWidth));
+        marker.SetAttributeValue("stroke-dasharray", "none");
+        this.Append(marker);
+    }
+
     public void DrawText(ImageStyle style, SurfaceText text)
     {
         if (string.IsNullOrWhiteSpace(text.Text))