Implement clipping in ProcessFormXObject()

src/UglyToad.PdfPig.Tests/Integration/StreamProcessorTests.cs

@@ -231,6 +231,11 @@ public override void ModifyClippingIntersect(FillingRule clippingRule)
                 // No op
             }
 
+            protected override void ClipToRectangle(PdfRectangle rectangle, FillingRule clippingRule)
+            {
+                // No op
+            }
+
             public override void PaintShading(NameToken shadingName)
             {
                 // No op

src/UglyToad.PdfPig.Tests/Integration/VisualVerification/SkiaHelpers/SkiaGlyphStreamProcessor.cs

@@ -206,6 +206,11 @@ public override void ModifyClippingIntersect(FillingRule clippingRule)
             // No op
         }
 
+        protected override void ClipToRectangle(PdfRectangle rectangle, FillingRule clippingRule)
+        {
+            // No op
+        }
+
         public override void PaintShading(NameToken shadingName)
         {
             // No op

src/UglyToad.PdfPig/Geometry/GeometryExtensions.cs

@@ -381,6 +381,19 @@ static double polarAngle(in PdfPoint point1, in PdfPoint point2)
         #endregion
 
         #region PdfRectangle
+        /// <summary>
+        /// Converts a <see cref="PdfRectangle"/> into its <see cref="PdfPath"/> representation.
+        /// </summary>
+        public static PdfPath ToPdfPath(this PdfRectangle rectangle)
+        {
+            var clippingSubpath = new PdfSubpath();
+            clippingSubpath.Rectangle(rectangle.BottomLeft.X,
+                rectangle.BottomLeft.Y,
+                rectangle.Width,
+                rectangle.Height);
+            return new PdfPath() { clippingSubpath };
+        }
+
         /// <summary>
         /// Whether the point is located inside the rectangle.
         /// </summary>

src/UglyToad.PdfPig/Graphics/BaseStreamProcessor.cs

@@ -145,15 +145,8 @@ protected BaseStreamProcessor(
         /// </summary>
         protected static PdfPath GetInitialClipping(CropBox cropBox)
         {
-            var cropBoxBounds = cropBox.Bounds;
-
-            // initiate CurrentClippingPath to cropBox
-            var clippingSubpath = new PdfSubpath();
-            clippingSubpath.Rectangle(cropBoxBounds.BottomLeft.X,
-                cropBoxBounds.BottomLeft.Y,
-                cropBoxBounds.Width,
-                cropBoxBounds.Height);
-            var clippingPath = new PdfPath() { clippingSubpath };
+            // Initiate CurrentClippingPath to cropBox
+            var clippingPath = cropBox.Bounds.ToPdfPath();
             clippingPath.SetClipping(FillingRule.EvenOdd);
             return clippingPath;
         }
@@ -581,7 +574,14 @@ protected virtual void ProcessFormXObject(StreamToken formStream, NameToken xObj
                 new MemoryInputBytes(contentStream),
                 ParsingOptions.Logger);
 
-            // 3. We don't respect clipping currently.
+            // 3. Clip according to the form dictionary's BBox entry.
+            if (formStream.StreamDictionary.TryGet<ArrayToken>(NameToken.Bbox, PdfScanner, out var bboxToken))
+            {
+                var points = bboxToken.Data.OfType<NumericToken>().Select(x => x.Double).ToArray();
+                PdfRectangle bbox = new PdfRectangle(points[0], points[1], points[2], points[3]);
+                PdfRectangle transformedBox = startState.CurrentTransformationMatrix.Transform(bbox);
+                ClipToRectangle(transformedBox, FillingRule.EvenOdd); // TODO - Check that Even Odd is valid
+            }
 
             // 4. Paint the objects.
             bool hasCircularReference = HasFormXObjectCircularReference(formStream, xObjectName, operations);
@@ -668,6 +668,9 @@ protected virtual bool HasFormXObjectCircularReference(StreamToken formStream,
         /// <inheritdoc/>
         public abstract void ModifyClippingIntersect(FillingRule clippingRule);
 
+        /// <inheritdoc/>
+        protected abstract void ClipToRectangle(PdfRectangle rectangle, FillingRule clippingRule);
+
         /// <inheritdoc/>
         public virtual void SetNamedGraphicsState(NameToken stateName)
         {

src/UglyToad.PdfPig/Graphics/ContentStreamProcessor.cs

@@ -422,7 +422,8 @@ public override void ModifyClippingIntersect(FillingRule clippingRule)
 
             if (ParsingOptions.ClipPaths)
             {
-                var currentClipping = GetCurrentState().CurrentClippingPath!;
+                var graphicsState = GetCurrentState();
+                var currentClipping = graphicsState.CurrentClippingPath!;
                 currentClipping.SetClipping(clippingRule);
 
                 var newClippings = CurrentPath.Clip(currentClipping, ParsingOptions.Logger);
@@ -432,11 +433,32 @@ public override void ModifyClippingIntersect(FillingRule clippingRule)
                 }
                 else
                 {
-                    GetCurrentState().CurrentClippingPath = newClippings;
+                    graphicsState.CurrentClippingPath = newClippings;
                 }
             }
         }
 
+        protected override void ClipToRectangle(PdfRectangle rectangle, FillingRule clippingRule)
+        {
+            // https://github.com/apache/pdfbox/blob/f4bfe47de37f6fe69e8f98b164c3546facfd5e91/pdfbox/src/main/java/org/apache/pdfbox/contentstream/PDFStreamEngine.java#L611
+            var graphicsState = GetCurrentState();
+            var clip = rectangle.ToPdfPath();
+            clip.SetClipping(clippingRule);
+
+            var currentClipping = graphicsState.CurrentClippingPath!;
+            currentClipping.SetClipping(clippingRule);
+            var newClippings = clip.Clip(currentClipping, ParsingOptions.Logger);
+
+            if (newClippings is null)
+            {
+                ParsingOptions.Logger.Warn("Empty clipping path found. Clipping path not updated.");
+            }
+            else
+            {
+                graphicsState.CurrentClippingPath = newClippings;
+            }
+        }
+
         protected override void RenderInlineImage(InlineImage inlineImage)
         {
             images.Add(Union<XObjectContentRecord, InlineImage>.Two(inlineImage));