Support blend mode and better handling of transparency group XObjects

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

@@ -24,7 +24,7 @@ public static class PdfToImageHelper
         private static SKBitmap createEmptyDiffImage(int minWidth, int minHeight, int maxWidth,
             int maxHeight)
         {
-            using (SKBitmap bim3 = new SKBitmap(new SKImageInfo(maxWidth, maxHeight, SKColorType.Rgb888x))) 
+            var bim3 = new SKBitmap(new SKImageInfo(maxWidth, maxHeight, SKColorType.Rgb888x));
             using (SKCanvas canvas = new SKCanvas(bim3))
             {
                 if (minWidth != maxWidth || minHeight != maxHeight)
@@ -45,14 +45,14 @@ private static SKBitmap createEmptyDiffImage(int minWidth, int minHeight, int ma
 
         private const byte _threshold = 2;
 
-        private static SKBitmap diffImages(SKBitmap bim1, SKBitmap bim2)
+        private static SKBitmap? diffImages(SKBitmap bim1, SKBitmap bim2)
         {
             int minWidth = Math.Min(bim1.Width, bim2.Width);
             int minHeight = Math.Min(bim1.Height, bim2.Height);
             int maxWidth = Math.Max(bim1.Width, bim2.Width);
             int maxHeight = Math.Max(bim1.Height, bim2.Height);
 
-            SKBitmap bim3 = null;
+            SKBitmap? bim3 = null;
             if (minWidth != maxWidth || minHeight != maxHeight)
             {
                 bim3 = createEmptyDiffImage(minWidth, minHeight, maxWidth, maxHeight);
@@ -121,7 +121,7 @@ public static bool TestResizeSinglePage(string pdfFile, int pageNumber, string e
                 using (var document = PdfDocument.Open(docPath, SkiaRenderingParsingOptions.Instance))
                 {
                     document.AddSkiaPageFactory();
-                    using (var actual = document.GetPageAsSKBitmap(pageNumber, scale))
+                    using (var actual = document.GetPageAsSKBitmap(pageNumber, scale, SKColors.White))
                     {
                         var skInfo = new SKImageInfo()
                         {
@@ -150,7 +150,7 @@ public static bool TestResizeSinglePage(string pdfFile, int pageNumber, string e
                                     return true;
                                 }
 
-                                SKBitmap bim3 = diffImages(expectedResize, actualResize);
+                                using var bim3 = diffImages(expectedResize, actualResize);
                                 if (bim3 is null)
                                 {
                                     return true;
@@ -189,7 +189,7 @@ public static bool TestSinglePage(string pdfFile, int pageNumber, string expecte
                 using (var document = PdfDocument.Open(docPath, SkiaRenderingParsingOptions.Instance))
                 {
                     document.AddSkiaPageFactory();
-                    using (var actual = document.GetPageAsSKBitmap(pageNumber, scale))
+                    using (var actual = document.GetPageAsSKBitmap(pageNumber, scale, SKColors.White))
                     {
                         if (filesAreIdentical(expected, actual))
                         {

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

@@ -504,6 +504,11 @@ public class TestRendering
                 "GHOSTSCRIPT-698721-1-rotated_1.png",
                 "GHOSTSCRIPT-698721-1-rotated.pdf", 1, 2
             },
+            new object[]
+            {
+                "blend_opacity_1.png",
+                "blend_opacity.pdf", 1, 2
+            },
         };
 
         [Theory(Skip = "for debugging purpose.")]

UglyToad.PdfPig.Rendering.Skia.Tests/UglyToad.PdfPig.Rendering.Skia.Tests.csproj

@@ -32,6 +32,9 @@
 	  <None Update="Documents\Apitron.PDF.Kit.Samples_patternFill-rotated.pdf">
 	    <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
 	  </None>
+	  <None Update="Documents\blend_opacity.pdf">
+	    <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+	  </None>
 	  <None Update="Documents\caly-issues-56-1.pdf">
 	    <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
 	  </None>
@@ -365,6 +368,9 @@
 	  <None Update="ExpectedImages\pdfpig_skia\Apitron.PDF.Kit.Samples_patternFill-rotated_1.png">
 	    <CopyToOutputDirectory>Always</CopyToOutputDirectory>
 	  </None>
+	  <None Update="ExpectedImages\pdfpig_skia\blend_opacity_1.png">
+	    <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+	  </None>
 	  <None Update="ExpectedImages\pdfpig_skia\caly-issues-56-1_1.png">
 	    <CopyToOutputDirectory>Always</CopyToOutputDirectory>
 	  </None>

UglyToad.PdfPig.Rendering.Skia/Helpers/SKPaintCache.cs

@@ -26,9 +26,7 @@ internal sealed class SKPaintCache : IDisposable
         private readonly bool _isAntialias;
 
         private readonly Dictionary<int, SKPaint> _cache = new();
-
-        private readonly SKPaint _antialiasingPaint;
-        private readonly SKPaint _noAntialiasingPaint;
+        private readonly Dictionary<(bool, BlendMode), SKPaint> _imagePaintCache = new();
 
 #if DEBUG
         private readonly SKPaint _imageDebugPaint;
@@ -38,9 +36,7 @@ public SKPaintCache(bool isAntialias, float minimumLineWidth)
         {
             _isAntialias = isAntialias;
             // minimumLineWidth not in use
-            _antialiasingPaint = new SKPaint() { IsAntialias = true };
 
-            _noAntialiasingPaint = new SKPaint() { IsAntialias = false };
 #if DEBUG
             _imageDebugPaint = new SKPaint()
             {
@@ -53,15 +49,15 @@ public SKPaintCache(bool isAntialias, float minimumLineWidth)
         }
 
         private static int GetPaintKey(IColor color, double alpha, bool stroke, float? strokeWidth, LineJoinStyle? joinStyle,
-            LineCapStyle? capStyle, LineDashPattern? dashPattern)
+            LineCapStyle? capStyle, LineDashPattern? dashPattern, BlendMode blendMode)
         {
-            return HashCode.Combine(color, alpha, stroke, strokeWidth, joinStyle, capStyle, GetHash(dashPattern));
+            return HashCode.Combine(color, alpha, stroke, strokeWidth, joinStyle, capStyle, GetHash(dashPattern), blendMode);
         }
 
         public SKPaint GetPaint(IColor color, double alpha, bool stroke, float? strokeWidth, LineJoinStyle? joinStyle,
-            LineCapStyle? capStyle, LineDashPattern? dashPattern)
+            LineCapStyle? capStyle, LineDashPattern? dashPattern, BlendMode blendMode)
         {
-            var key = GetPaintKey(color, alpha, stroke, strokeWidth, joinStyle, capStyle, dashPattern);
+            var key = GetPaintKey(color, alpha, stroke, strokeWidth, joinStyle, capStyle, dashPattern, blendMode);
 
             if (_cache.TryGetValue(key, out var paint))
             {
@@ -73,6 +69,7 @@ public SKPaint GetPaint(IColor color, double alpha, bool stroke, float? strokeWi
                 IsAntialias = _isAntialias,
                 Color = color.ToSKColor(alpha),
                 Style = stroke ? SKPaintStyle.Stroke : SKPaintStyle.Fill,
+                BlendMode = blendMode.ToSKBlendMode()
             };
 
             if (stroke)
@@ -104,18 +101,25 @@ private static int GetHash(LineDashPattern? dashPattern)
             return key;
         }
 
-        public SKPaint GetPaint(IPdfImage pdfImage)
+        public SKPaint GetPaint(IPdfImage pdfImage, BlendMode blendMode)
         {
-            if (!pdfImage.Interpolate)
+            // For non-Normal blend modes, use general cache with ValueTuple key
+            var key = (pdfImage.Interpolate, blendMode);
+
+            if (_imagePaintCache.TryGetValue(key, out var paint))
             {
-                return _noAntialiasingPaint;
+                return paint;
             }
-            return _antialiasingPaint;
-        }
 
-        public SKPaint GetAntialiasing()
-        {
-            return _antialiasingPaint;
+            paint = new SKPaint
+            {
+                IsAntialias = pdfImage.Interpolate,
+                BlendMode = blendMode.ToSKBlendMode()
+            };
+
+            _imagePaintCache[key] = paint;
+
+            return paint;
         }
 
 #if DEBUG
@@ -130,15 +134,18 @@ public void Dispose()
 #if DEBUG
             _imageDebugPaint.Dispose();
 #endif
-            _antialiasingPaint.Dispose();
-            _noAntialiasingPaint.Dispose();
-
             foreach (var pair in _cache)
             {
                 pair.Value.PathEffect?.Dispose();
                 pair.Value.Dispose();
             }
             _cache.Clear();
+
+            foreach (var pair in _imagePaintCache)
+            {
+                pair.Value.Dispose();
+            }
+            _imagePaintCache.Clear();
         }
     }
 }

UglyToad.PdfPig.Rendering.Skia/Helpers/SkiaExtensions.cs

@@ -275,14 +275,8 @@ public static SKMatrix ToSkMatrix(this TransformationMatrix transformationMatrix
                 0, 0, 1);
         }
 
-        private static readonly bool doBlending = false;
-
         public static SKBlendMode ToSKBlendMode(this BlendMode blendMode)
         {
-            if (!doBlending)
-            {
-                return SKBlendMode.SrcOver;
-            }
 
             // https://pdfium.googlesource.com/pdfium/+/refs/heads/main/core/fxge/skia/fx_skia_device.cpp
             switch (blendMode)

UglyToad.PdfPig.Rendering.Skia/PdfPigExtensions.cs

@@ -39,17 +39,23 @@ public static void AddSkiaPageFactory(this PdfDocument document)
         /// <param name="document">The pdf document.</param>
         /// <param name="pageNumber">The number of the page to return, this starts from 1.</param>
         /// <param name="scale">The scale factor to use when rendering the page.</param>
+        /// <param name="clearColor">Optional background color to clear the canvas with before rendering. If null, the canvas is not cleared.</param>
         /// <returns>The <see cref="SKBitmap"/>.</returns>
-        public static SKBitmap GetPageAsSKBitmap(this PdfDocument document, int pageNumber, float scale = 1)
+        public static SKBitmap GetPageAsSKBitmap(this PdfDocument document, int pageNumber, float scale = 1, SKColor? clearColor = null)
         {
             using (var picture = document.GetPage<SKPicture>(pageNumber))
             {
-                var size = new SKSizeI((int)Math.Ceiling(picture.CullRect.Width * scale), (int)Math.Ceiling(picture.CullRect.Height * scale));
+                var page = document.GetPage(pageNumber);
+                var size = new SKSizeI((int)Math.Ceiling(page.Width * scale), (int)Math.Ceiling(page.Height * scale));
                 var scaleMatrix = SKMatrix.CreateScale(scale, scale);
 
                 var bitmap = new SKBitmap(size.Width, size.Height);
                 using (var canvas = new SKCanvas(bitmap))
                 {
+                    if (clearColor.HasValue)
+                    {
+                        canvas.Clear(clearColor.Value);
+                    }
                     canvas.DrawPicture(picture, in scaleMatrix);
                     return bitmap;
                 }
@@ -67,7 +73,7 @@ public static SKBitmap GetPageAsSKBitmap(this PdfDocument document, int pageNumb
         public static MemoryStream GetPageAsPng(this PdfDocument document, int pageNumber, float scale = 1, int quality = 100)
         {
             var ms = new MemoryStream();
-            using (var bitmap = document.GetPageAsSKBitmap(pageNumber, scale))
+            using (var bitmap = document.GetPageAsSKBitmap(pageNumber, scale, SKColors.White))
             {
                 bitmap.Encode(ms, SKEncodedImageFormat.Png, quality);
                 ms.Position = 0;

UglyToad.PdfPig.Rendering.Skia/SkiaStreamProcessor.Annotations.cs

@@ -42,19 +42,6 @@ internal partial class SkiaStreamProcessor
         /// </summary>
         public static readonly RGBColor DefaultRequiredFieldsHighlightColor = new RGBColor(1, 0, 0);
 
-        private static bool IsAnnotationBelowText(Annotation annotation)
-        {
-            // TODO - Very hackish
-            switch (annotation.Type)
-            {
-                case AnnotationType.Highlight:
-                    return true;
-
-                default:
-                    return false;
-            }
-        }
-
         private static bool ShouldRender(Annotation annotation)
         {
             // cf. ISO 32000-2:2020(E) - Table 167 — Annotation flags
@@ -70,11 +57,11 @@ private static bool ShouldRender(Annotation annotation)
 
         private readonly Lazy<Annotation[]> _annotations;
 
-        private void DrawAnnotations(bool isBelowText)
+        private void DrawAnnotations()
         {
             // https://github.com/apache/pdfbox/blob/trunk/pdfbox/src/main/java/org/apache/pdfbox/rendering/PageDrawer.java
             // https://github.com/apache/pdfbox/blob/c4b212ecf42a1c0a55529873b132ea338a8ba901/pdfbox/src/main/java/org/apache/pdfbox/contentstream/PDFStreamEngine.java#L312
-            foreach (Annotation annotation in _annotations.Value.Where(a => IsAnnotationBelowText(a) == isBelowText))
+            foreach (Annotation annotation in _annotations.Value)
             {
                 // Check if visible
                 if (!ShouldRender(annotation))

UglyToad.PdfPig.Rendering.Skia/SkiaStreamProcessor.Glyph.cs

@@ -126,7 +126,7 @@ private void ShowVectorFontGlyph(SKPath path, IColor strokingColor, IColor nonSt
                     else
                     {
                         var fillBrush = _paintCache.GetPaint(nonStrokingColor, currentState.AlphaConstantNonStroking, false,
-                            null, null, null, null);
+                            null, null, null, null, currentState.BlendMode);
                         _canvas.DrawPath(transformedPath, fillBrush);
                     }
                 }
@@ -136,7 +136,7 @@ private void ShowVectorFontGlyph(SKPath path, IColor strokingColor, IColor nonSt
                     // Then stroke
                     var strokePaint = _paintCache.GetPaint(strokingColor, currentState.AlphaConstantStroking, true,
                         (float)currentState.LineWidth, currentState.JoinStyle, currentState.CapStyle,
-                        currentState.LineDashPattern);
+                        currentState.LineDashPattern, currentState.BlendMode);
                     _canvas.DrawPath(transformedPath, strokePaint);
                 }
             }
@@ -181,12 +181,15 @@ private void ShowNonVectorFontGlyph(IFont font, IColor strokingColor, IColor non
 
             var color = style == SKPaintStyle.Stroke ? strokingColor : nonStrokingColor; // TODO - very not correct
 
+            var currentState = GetCurrentState();
+
             using (var skFont = drawTypeface.Typeface.ToFont(1f))
             using (var paint = new SKPaint())
             {
                 paint.Style = style.Value;
-                paint.Color = color.ToSKColor(GetCurrentState().AlphaConstantNonStroking);
+                paint.Color = color.ToSKColor(currentState.AlphaConstantNonStroking);
                 paint.IsAntialias = _antiAliasing;
+                paint.BlendMode = currentState.BlendMode.ToSKBlendMode();
 
                 // TODO - Benchmark with SPARC - v9 Architecture Manual.pdf
                 // as _canvas.DrawShapedText(unicode, startBaseLine, fontPaint); as very slow without 'Shaper' caching