handle empty empty stacks in PopState()

Author: BobLd

UglyToad.PdfPig.Rendering.Skia.Tests/Documents/JD5008.pdf

@@ -722,14 +722,20 @@ public class TestRendering
 
             new object[]
             {
-                "GWG060_Shading_x1a_1.png", // reference image on the left is wrong
+                "GWG060_Shading_x1a_1.png",
                 "GWG060_Shading_x1a.pdf", 1, 2
             },
             new object[]
             {
                 "GWG061_Shading_x1a_1.png",
                 "GWG061_Shading_x1a.pdf", 1, 2
             },
+
+            new object[]
+            {
+                "JD5008_2.png",
+                "JD5008.pdf", 2, 2
+            },
         };
 
         [Theory(Skip = "for debugging purpose.")]

UglyToad.PdfPig.Rendering.Skia.Tests/ExpectedImages/pdfpig_skia/JD5008_2.png

@@ -326,6 +326,9 @@
 		<None Update="Documents\ICML03-081.pdf">
 			<CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
 		</None>
+		<None Update="Documents\JD5008.pdf">
+		  <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+		</None>
 		<None Update="Documents\journal.pone.0196757.pdf">
 			<CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
 		</None>
@@ -698,6 +701,9 @@
 		<None Update="ExpectedImages\pdfpig_skia\issue-50_2.png">
 			<CopyToOutputDirectory>Always</CopyToOutputDirectory>
 		</None>
+		<None Update="ExpectedImages\pdfpig_skia\JD5008_2.png">
+		  <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+		</None>
 		<None Update="ExpectedImages\pdfpig_skia\journal.pone.0196757_1.png">
 			<CopyToOutputDirectory>Always</CopyToOutputDirectory>
 		</None>

UglyToad.PdfPig.Rendering.Skia.Tests/TestRendering.cs

@@ -184,7 +184,7 @@ protected override void ProcessOperations(IReadOnlyList<IGraphicsStateOperation>
                 {
                     _token.ThrowIfCancellationRequested();
                 }
-                
+
                 operations[i].Run(this);
             }
         }
@@ -195,7 +195,7 @@ public override void PopState()
             // composited into the still-open offscreen buffer. DstIn keeps only the parts of
             // the layer where the mask has alpha; the LumaColor filter converts the source
             // colour to luminosity-as-alpha for /Luminosity-subtype masks.
-            var maskImage = _pendingMasks.Pop();
+            var maskImage = _pendingMasks.Count > 0 ? _pendingMasks.Pop() : null;
             if (maskImage is not null)
             {
                 _canvas.Save();
@@ -204,11 +204,9 @@ public override void PopState()
                 // covering the same logical bounds as the layer).
                 _canvas.SetMatrix(SKMatrix.Identity);
 
-                using var maskPaint = new SKPaint
-                {
-                    BlendMode = SKBlendMode.DstIn,
-                    ColorFilter = SKColorFilter.CreateLumaColor()
-                };
+                using var maskPaint = new SKPaint();
+                maskPaint.BlendMode = SKBlendMode.DstIn;
+                maskPaint.ColorFilter = SKColorFilter.CreateLumaColor();
 
                 _canvas.DrawImage(maskImage, SKRect.Create(0, 0, _width, _height), maskPaint);
                 _canvas.Restore();
@@ -219,7 +217,7 @@ public override void PopState()
             _canvas.Restore();
 
             // Dispose layer paint if one was used for this state
-            var layerPaint = _transparencyLayerPaints.Pop();
+            var layerPaint = _transparencyLayerPaints.Count > 0 ? _transparencyLayerPaints.Pop() : null;
             layerPaint?.Dispose();
 
             EndPath();