RED-7686: Specific hidden text in specific file is not removed

* extend invisible Element removal to Form XObjects BBoxes

src/main/java/com/iqser/red/pdftronlogic/commons/InvisibleElementRemovalService.java

@@ -8,6 +8,7 @@ import java.awt.geom.Rectangle2D;
 import java.io.InputStream;
 import java.io.OutputStream;
 import java.util.ArrayList;
+import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
@@ -46,6 +47,7 @@ public class InvisibleElementRemovalService {
      * handled cases:
      * -Text which is transparent or is set to not render
      * -Elements outside of clipping path
+     * -Elements outside of Form XObjects
      * -Elements that have been painted over by visible and filled Paths
      * -Elements with the same color as background
      * unhandled cases:
@@ -235,6 +237,8 @@ public class InvisibleElementRemovalService {
             // writer needs to be newly initialized when entering a new content stream
             // see ElementEditTest in PDFTron (https://www.pdftron.com/documentation/samples/android/java/ElementEditTest)
             ElementWriter formWriter = new ElementWriter();
+            context.clippingPathStack().enterNewGState();
+            context.clippingPathStack().intersectClippingPath(new GeneralPath(Converter.toRectangle2D(formElement.getBBox())));
             context.reader().formBegin();
             formWriter.begin(formObj);
 
@@ -245,6 +249,7 @@ public class InvisibleElementRemovalService {
             formWriter.end();
             formWriter.destroy();
             context.reader().end();
+            context.clippingPathStack().leaveGState();
         }
     }
 

src/test/java/com/iqser/red/pdftronlogic/commons/InvisibleElementRemovalServiceTest.java

@@ -53,6 +53,34 @@ class InvisibleElementRemovalServiceTest {
     }
 
 
+    @Test
+    @SneakyThrows
+    void removeInvisibleTextClippedByFormObjects() {
+
+        String fileName = "files/invisibleTextInNestedFormObjects.pdf";
+        String resultFileName = OsUtils.createTmpFileName(fileName, "INVISIBLE_REMOVAL");
+        String deltaResultFileName = OsUtils.createTmpFileName(fileName, "INVISIBLE_REMOVAL_DELTA");
+        try (var in = this.getClass().getClassLoader().getResourceAsStream(fileName); var out = new FileOutputStream(resultFileName)) {
+            invisibleElementRemovalService.removeInvisibleElements(in, out, false);
+        }
+
+        try (var in = this.getClass().getClassLoader().getResourceAsStream(fileName); var out = new FileOutputStream(deltaResultFileName)) {
+            invisibleElementRemovalService.removeInvisibleElements(in, out, true);
+        }
+        try (var in = new FileInputStream(resultFileName)) {
+            String text = extractAllTextFromDocument(in);
+            assertThat(text).isBlank();
+        }
+        try (var in = new FileInputStream(deltaResultFileName)) {
+            String[] text = extractAllTextFromDocument(in).split("\n");
+            assertThat(text).contains(":Bold S-enantiomer form if two codes are supplied",
+                    "Red : Only observed in laboratory soil studies",
+                    "Green : Observed in both laboratory soil studies and lysimeter leachate",
+                    "Blue : Only observed in lysimeter leachate");
+        }
+    }
+
+
     @Test
     @SneakyThrows
     void removeInvisibleElementsWithColoredBackground() {