Fix wrong empty paragraphs rendering

Resolve DEVSIX-500

Author: ars18wrw

io/src/main/java/com/itextpdf/io/LogMessageConstant.java

@@ -65,6 +65,11 @@ public class LogMessageConstant {
      */
     public static final String ONLY_ONE_OF_ARTBOX_OR_TRIMBOX_CAN_EXIST_IN_THE_PAGE = "Only one of artbox or trimbox can exist on the page. The trimbox will be deleted";
 
+    /**
+     * Log message.
+     */
+    public static final String RECTANGLE_HAS_NEGATIVE_OR_ZERO_SIZES = "The {0} rectangle has negative or zero sizes. It will not be displayed.";
+
     /**
      * Log message.
      */

layout/src/main/java/com/itextpdf/layout/renderer/AbstractRenderer.java

@@ -1,5 +1,6 @@
 package com.itextpdf.layout.renderer;
 
+import com.itextpdf.io.LogMessageConstant;
 import com.itextpdf.kernel.color.Color;
 import com.itextpdf.kernel.font.PdfFont;
 import com.itextpdf.kernel.geom.Rectangle;
@@ -18,12 +19,16 @@
 import com.itextpdf.layout.layout.LayoutArea;
 import com.itextpdf.layout.layout.LayoutPosition;
 
+import java.text.MessageFormat;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.EnumMap;
 import java.util.List;
 import java.util.Map;
 
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
 /**
  * Defines the most common properties and behavior that are shared by most
  * {@link IRenderer} implementations. All default Renderers are subclasses of
@@ -52,7 +57,7 @@ public AbstractRenderer() {
 
     /**
      * Creates a renderer for the specified layout element.
-     * 
+     *
      * @param modelElement the layout element that will be drawn by this renderer
      */
     public AbstractRenderer(IPropertyContainer modelElement) {
@@ -247,7 +252,7 @@ public void draw(DrawContext drawContext) {
     /**
      * Draws a background layer if it is defined by a key {@link Property#BACKGROUND}
      * in either the layout element or this {@link IRenderer} itself.
-     * 
+     *
      * @param drawContext the context (canvas, document, etc) of this drawing operation.
      */
     public void drawBackground(DrawContext drawContext) {
@@ -261,6 +266,11 @@ public void drawBackground(DrawContext drawContext) {
                 drawContext.getCanvas().openTag(new CanvasArtifact());
             }
             Rectangle backgroundArea = applyMargins(bBox, false);
+            if (backgroundArea.getWidth() <= 0 || backgroundArea.getHeight() <= 0) {
+                Logger logger = LoggerFactory.getLogger(AbstractRenderer.class);
+                logger.error(MessageFormat.format(LogMessageConstant.RECTANGLE_HAS_NEGATIVE_OR_ZERO_SIZES, "background"));
+                return;
+            }
             drawContext.getCanvas().saveState().setFillColor(background.getColor()).
                     rectangle(backgroundArea.getX() - background.getExtraLeft(), backgroundArea.getY() - background.getExtraBottom(),
                             backgroundArea.getWidth() + background.getExtraLeft() + background.getExtraRight(),
@@ -276,7 +286,7 @@ public void drawBackground(DrawContext drawContext) {
     /**
      * Performs the drawing operation for all {@link IRenderer children}
      * of this renderer.
-     * 
+     *
      * @param drawContext the context (canvas, document, etc) of this drawing operation.
      */
     public void drawChildren(DrawContext drawContext) {
@@ -289,7 +299,7 @@ public void drawChildren(DrawContext drawContext) {
      * Performs the drawing operation for the border of this renderer, if
      * defined by any of the {@link Property#BORDER} values in either the layout
      * element or this {@link IRenderer} itself.
-     * 
+     *
      * @param drawContext the context (canvas, document, etc) of this drawing operation.
      */
     public void drawBorder(DrawContext drawContext) {
@@ -306,6 +316,11 @@ public void drawBorder(DrawContext drawContext) {
             float leftWidth = borders[3] != null ? borders[3].getWidth() : 0;
 
             Rectangle bBox = getBorderAreaBBox();
+            if (bBox.getWidth() <= 0 || bBox.getHeight() <= 0) {
+                Logger logger = LoggerFactory.getLogger(AbstractRenderer.class);
+                logger.error(MessageFormat.format(LogMessageConstant.RECTANGLE_HAS_NEGATIVE_OR_ZERO_SIZES, "border"));
+                return;
+            }
             float x1 = bBox.getX();
             float y1 = bBox.getY();
             float x2 = bBox.getX() + bBox.getWidth();

layout/src/main/java/com/itextpdf/layout/renderer/ParagraphRenderer.java

@@ -2,6 +2,7 @@
 
 import com.itextpdf.kernel.geom.Rectangle;
 import com.itextpdf.layout.Property;
+import com.itextpdf.layout.border.Border;
 import com.itextpdf.layout.element.Paragraph;
 import com.itextpdf.layout.layout.LayoutArea;
 import com.itextpdf.layout.layout.LayoutContext;
@@ -65,6 +66,20 @@ public LayoutResult layout(LayoutContext layoutContext) {
             currentRenderer.addChild(child);
         }
 
+        if (0 == childRenderers.size()) {
+            anythingPlaced = true;
+            currentRenderer = null;
+            setProperty(Property.MARGIN_TOP, 0);
+            setProperty(Property.MARGIN_RIGHT, 0);
+            setProperty(Property.MARGIN_BOTTOM, 0);
+            setProperty(Property.MARGIN_LEFT, 0);
+            setProperty(Property.PADDING_TOP, 0);
+            setProperty(Property.PADDING_RIGHT, 0);
+            setProperty(Property.PADDING_BOTTOM, 0);
+            setProperty(Property.PADDING_LEFT, 0);
+            setProperty(Property.BORDER, Border.NO_BORDER);
+        }
+
         float lastYLine = layoutBox.getY() + layoutBox.getHeight();
         Property.Leading leading = getProperty(Property.LEADING);
         float leadingValue = 0;

layout/src/test/java/com/itextpdf/layout/DefaultLayoutTest.java

@@ -1,22 +1,26 @@
 package com.itextpdf.layout;
 
-import com.itextpdf.kernel.geom.PageSize;
+import com.itextpdf.io.LogMessageConstant;
 import com.itextpdf.kernel.color.Color;
+import com.itextpdf.kernel.geom.PageSize;
 import com.itextpdf.kernel.pdf.PdfDocument;
 import com.itextpdf.kernel.pdf.PdfWriter;
 import com.itextpdf.kernel.utils.CompareTool;
-import com.itextpdf.test.annotations.type.IntegrationTest;
+import com.itextpdf.layout.border.SolidBorder;
 import com.itextpdf.layout.element.AreaBreak;
 import com.itextpdf.layout.element.Paragraph;
 import com.itextpdf.layout.element.Text;
 import com.itextpdf.test.ExtendedITextTest;
-
+import com.itextpdf.test.annotations.LogMessage;
+import com.itextpdf.test.annotations.LogMessages;
+import com.itextpdf.test.annotations.type.IntegrationTest;
 
 import java.io.FileOutputStream;
 import java.io.IOException;
 
 import org.junit.Assert;
 import org.junit.BeforeClass;
+import org.junit.Ignore;
 import org.junit.Test;
 import org.junit.experimental.categories.Category;
 
@@ -66,4 +70,63 @@ public void rendererTest01() throws IOException,  InterruptedException {
         Assert.assertNull(new CompareTool().compareByContent(outFileName, cmpFileName, destinationFolder, "diff"));
     }
 
+    @Test
+    @LogMessages(messages = {
+            @LogMessage(messageTemplate = LogMessageConstant.RECTANGLE_HAS_NEGATIVE_OR_ZERO_SIZES)
+    })
+    public void emptyParagraphsTest01() throws IOException,  InterruptedException {
+        String outFileName = destinationFolder + "emptyParagraphsTest01.pdf";
+        String cmpFileName = sourceFolder + "cmp_emptyParagraphsTest01.pdf";
+        PdfDocument pdfDocument = new PdfDocument(new PdfWriter(new FileOutputStream(outFileName)));
+
+        Document document = new Document(pdfDocument);
+
+        // the next 3 lines should not cause any effect
+        document.add(new Paragraph());
+        document.add(new Paragraph().setBackgroundColor(Color.GREEN));
+        document.add(new Paragraph().setBorder(new SolidBorder(Color.BLUE, 3)));
+
+        document.add(new Paragraph("Hello! I'm the first paragraph added to the document. Am i right?"));
+        document.add(new Paragraph().setHeight(50));
+        document.add(new Paragraph("Hello! I'm the second paragraph added to the document. Am i right?"));
+
+        document.close();
+
+        Assert.assertNull(new CompareTool().compareByContent(outFileName, cmpFileName, destinationFolder, "diff"));
+    }
+
+    @Test
+    @Ignore
+    public void emptyParagraphsTest02() throws IOException,  InterruptedException {
+        String outFileName = destinationFolder + "emptyParagraphsTest02.pdf";
+        String cmpFileName = sourceFolder + "cmp_emptyParagraphsTest02.pdf";
+        PdfDocument pdfDocument = new PdfDocument(new PdfWriter(new FileOutputStream(outFileName)));
+
+        Document document = new Document(pdfDocument);
+
+        document.add(new Paragraph("\n\n\n"));
+        document.add(new Paragraph("a\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\nb\n\n\n\n\n\n\n\n\n\n\n\n\n\n\nc\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\nd\n\n\n\n\n\n\n\n\n\n\n\n\n\n\ne"));
+
+        document.close();
+
+        Assert.assertNull(new CompareTool().compareByContent(outFileName, cmpFileName, destinationFolder, "diff"));
+    }
+
+    @Test
+    @Ignore
+    public void emptyParagraphsTest03() throws IOException,  InterruptedException {
+        String outFileName = destinationFolder + "emptyParagraphsTest03.pdf";
+//         String cmpFileName = sourceFolder + "cmp_emptyParagraphsTest03.pdf";
+        PdfDocument pdfDocument = new PdfDocument(new PdfWriter(new FileOutputStream(outFileName)));
+
+        Document document = new Document(pdfDocument);
+
+        document.add(new Paragraph("c\nb"));
+//        document.add(new Paragraph("a a\nb"));
+
+        document.close();
+
+//        Assert.assertNull(new CompareTool().compareByContent(outFileName, cmpFileName, destinationFolder, "diff"));
+    }
+
 }