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https://issues.apache.org/jira/browse/PDFBOX-5230?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17929808#comment-17929808
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Daniel Gredler commented on PDFBOX-5230:
----------------------------------------
[~tilman] I wanted to have another look at this one, and perhaps create a fix
PR. I think I'll use the "Save as PDF" functionality in LibreOffice Writer and
in the online version of Microsoft Office to check their behavior, and if their
behavior matches, assume that's "best practice" (or at least a good starting
point). Does this sound like a good foundation for a possible fix for this
issue? Also, if you have any other thoughts or advice on this one, I'm all ears.
> Zero-width non-joiner characters visible in generated PDF
> ---------------------------------------------------------
>
> Key: PDFBOX-5230
> URL: https://issues.apache.org/jira/browse/PDFBOX-5230
> Project: PDFBox
> Issue Type: Bug
> Components: FontBox, PDModel, Writing
> Affects Versions: 2.0.16
> Reporter: Daniel Gredler
> Priority: Major
> Attachments: Af.pdf, zwnj-pdfkit.pdf, zwnj.pdf, zwnj.png
>
>
> I'd like to use the [zero-width
> non-joiner|https://en.wikipedia.org/wiki/Zero-width_non-joiner] (ZWNJ)
> character to prevent character shaping in some cases when using Arabic and
> Indic scripts. This works correctly using some fonts like Arial Unicode
> (character shaping is prevented and no ZWNJ glyph is visible in the PDF), but
> does not work correctly when using fonts like Tahoma or Google Noto Sans
> Regular, where the ZWNJ character is visible in the PDF. The ZWNJ glyph is
> not visible when using these fonts in other programs, like Microsoft Word.
> I suspect that the `advanceWidth` settings in the `hmtx` table should be
> taken into account somehow but are not, because the `advanceWidth` for this
> glyph is 0 in both of these fonts which are erroneously generating visual
> artifacts for the ZWNJ character (Tahoma and Google Noto Sans Regular).
> Test case generating the attached PDF file:
> {code:java}
> public class ZwnjTest {
> public static void main(String[] args) throws IOException {
> try (PDDocument document = new PDDocument()) {
> PDPage page = new PDPage(PDRectangle.LETTER);
> document.addPage(page);
> try (PDPageContentStream stream = new
> PDPageContentStream(document, page)) {
> // Tahoma: ZWNJ glyph is a vertical bar, but advanceWidth in
> hmtx table is 0 -> shown in PDF anyway (unexpected)
> PDFont tahoma = PDType0Font.load(document, new
> File("C:/Windows/Fonts/tahoma.ttf"));
> stream.beginText();
> stream.setFont(tahoma, 20);
> stream.newLineAtOffset(50, 650);
> stream.showText("t\u200Ce\u200Cs\u200Ct\u200C \u200C1"); //
> U+200C = zero width non-joiner
> stream.endText();
> // Arial Unicode: ZWNJ glyph contains no outline -> not shown
> in PDF (as expected)
> PDFont arialu = PDType0Font.load(document, new
> File("C:/Windows/Fonts/ARIALUNI.TTF"));
> stream.beginText();
> stream.setFont(arialu, 20);
> stream.newLineAtOffset(50, 600);
> stream.showText("t\u200Ce\u200Cs\u200Ct\u200C \u200C2"); //
> U+200C = zero width non-joiner
> stream.endText();
> // Google Noto Sans Regular: ZWNJ glyph is a vertical bar,
> but advanceWidth in hmtx table is 0 -> shown in PDF anyway (unexpected)
> PDFont gnotos = PDType0Font.load(document, new
> File("noto-sans-regular.ttf"));
> stream.beginText();
> stream.setFont(gnotos, 20);
> stream.newLineAtOffset(50, 550);
> stream.showText("t\u200Ce\u200Cs\u200Ct\u200C \u200C3"); //
> U+200C = zero width non-joiner
> stream.endText();
> }
> document.save("zwnj.pdf");
> }
> }
> }
> {code}
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