[PDFBOX-3992] Implement show text with positioning operator (TJ)

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 2.0.9, 3.0.0 PDFBox
• Component/s: PDModel
• Assignee: Tilman Hausherr
• Reporter: Dan Fickling
• Created: 05/Nov/17 04:05
• Updated: 24/Mar/18 09:41
• Resolved: 08/Nov/17 20:47

Description

Why: The TJ operator is required to properly implement text justification in unicode fonts. The word spacing operator (Tw) is not sufficient because of note[1] from the PDF specification.

Github user backslash47 has provided a basic implementation if that is of any help:
https://github.com/backslash47/pdfbox/commit/3c528295b16445e58dc9fe895f78384221452be2

Thanks,
Daniel.

[1] Note: Word spacing is applied to every occurrence of the single-byte character code 32 in a string when using a simple font or a composite font that defines code 32 as a single-byte code. It does not apply to occurrences of the byte value 32 in multiple-byte codes.

Example code:

import java.io.InputStream;
import java.util.ArrayList;
import java.util.List;

import org.apache.pdfbox.pdmodel.PDDocument;
import org.apache.pdfbox.pdmodel.PDPage;
import org.apache.pdfbox.pdmodel.PDPageContentStream;
import org.apache.pdfbox.pdmodel.PDPageContentStream.AppendMode;
import org.apache.pdfbox.pdmodel.common.PDRectangle;
import org.apache.pdfbox.pdmodel.font.PDFont;
import org.apache.pdfbox.pdmodel.font.PDType0Font;
import org.apache.pdfbox.util.Matrix;

public class TextWithPositioningExample {

	public static void main(String[] args) throws Exception {
		doIt("Hello World, this is a test!", "justify-example.pdf");
	}

	/**
	 * This example shows how to justify a string using the showTextWithPositioning method.
	 * First only spaces are adjusted, and then every letter.
	 */
	public static void doIt(String message, String outfile) throws Exception {

		// the document
		try (PDDocument doc = new PDDocument();
			 InputStream is = PDDocument.class.getResourceAsStream("/org/apache/pdfbox/resources/ttf/LiberationSans-Regular.ttf")) {

			final float FONT_SIZE = 20.0f;

			// Page 1
			PDFont font = PDType0Font.load(doc, is, true);
			//PDFont font = PDType1Font.COURIER;
			PDPage page = new PDPage(PDRectangle.A4);
			doc.addPage(page);
			
			// Get the non-justified string width in text space units.
			float stringWidth = font.getStringWidth(message) * FONT_SIZE;
			
			// Get the string height in text space units.
			float stringHeight = font.getFontDescriptor().getFontBoundingBox().getHeight() * FONT_SIZE;
			
			// Get the width we have to justify in.
			PDRectangle pageSize = page.getMediaBox();
			
			PDPageContentStream contentStream = new PDPageContentStream(doc,
					page, AppendMode.OVERWRITE, false);
		
			contentStream.beginText();
			contentStream.setFont(font, FONT_SIZE);
			
			// Start at top of page.
			contentStream.setTextMatrix(Matrix.getTranslateInstance(0, pageSize.getHeight() - stringHeight / 1000f));
			
			// First show non-justified.
			contentStream.showText(message);
			
			// Move to next line.
			contentStream.setTextMatrix(Matrix.getTranslateInstance(0, pageSize.getHeight() - ((stringHeight / 1000f) * 2)));
			
			// Now show word justified.
			// The space we have to make up, in text space units.
			float justifyWidth = ((pageSize.getWidth() * 1000f) - (stringWidth));
			
			List<Object> text = new ArrayList<>();
			String[] parts = message.split("\\s");
			
			float spaceWidth = (justifyWidth / (parts.length - 1)) / FONT_SIZE;

			for (int i = 0; i < parts.length; i++) {
				if (i != 0) {
					text.add(" ");
					// Positive values move to the left, negative to the right.
					text.add(Float.valueOf(-spaceWidth));
				}
				text.add(parts[i]);
			}
			contentStream.showTextWithPositioning(text.toArray());
			contentStream.setTextMatrix(Matrix.getTranslateInstance(0, pageSize.getHeight() - ((stringHeight / 1000f) * 3)));
			
			// Now show letter justified.
			text = new ArrayList<>();
			justifyWidth = ((pageSize.getWidth() * 1000f) - stringWidth);
			float extraLetterWidth = (justifyWidth / (message.codePointCount(0, message.length()) - 1)) / FONT_SIZE;
			
			for (int i = 0; i < message.length();) {
				if (i != 0) {
					text.add(Float.valueOf(-extraLetterWidth));
				}
				
				text.add(String.valueOf(Character.toChars(message.codePointAt(i))));
				
				i += Character.charCount(message.codePointAt(i));
			}
			contentStream.showTextWithPositioning(text.toArray());;
			
			// Finish up.
			contentStream.endText();
			contentStream.close();

			doc.save(outfile);
		}
	}
}