Text Manipulation

All text drawn by the creator package goes through StyledParagraph. UniPDF v5 removed the older Paragraph component and Creator.NewParagraph along with it, so c.NewStyledParagraph() is the only way to place text. The guides in this section cover styling it, and separately, editing text that is already in a PDF.

Chunks and styles

A styled paragraph is a list of TextChunk values, each with its own TextStyle. Append adds a chunk and returns it, which is how per-chunk styling is done:

p := c.NewStyledParagraph()

chunk := p.Append("bold and blue")
chunk.Style.Font = boldFont
chunk.Style.FontSize = 14
chunk.Style.Color = creator.ColorBlue

if err := c.Draw(p); err != nil {
    return err
}

SetText is Reset followed by Append: it discards every existing chunk and returns the single one it created. Reach for it when replacing content, not when adding to it.

The paragraph-level setters cover the whole paragraph. SetFont, SetFontSize, SetFontColor and SetStyle each write the paragraph’s default style and then walk the chunks that already exist, applying the change to all of them. Call order relative to SetText therefore does not matter, and a per-chunk style set earlier will be overwritten. Note the name: the color setter is SetFontColor. There is no SetColor on a styled paragraph.

Assigning chunk.Style = someTextStyle replaces the entire style, including the font and color. Setting one field, as in chunk.Style.FontSize = 14, leaves the rest of the style alone. Mixing the two in one paragraph is the usual cause of a chunk losing its font.

Writing direction is detected per chunk rather than configured. Any chunk whose text is right-to-left is reordered and reversed automatically, so Hebrew and Arabic need a font with the glyphs and nothing else. See right to left text.

Editing text in an existing PDF

Two unrelated approaches exist, and they are not interchangeable.

The content stream approach is what simple and advanced cover. You get full control and no dependency on text extraction, at the cost of handling font encoding and operator boundaries yourself. The extractor.Editor approach is higher level and is covered in search and replace.

Neither reflows the page. Both substitute glyphs in place and leave the positioning operators as they were, so a replacement of a different width will overlap the text after it or leave a gap.

Where to look

For text placed in a table cell see tables, and for reading text out of a PDF rather than writing it see extraction.