gopdf Documentation

gopdf is a Go library for generating PDF documents. Key features include:

• Unicode subfont embedding: Supports Chinese, Japanese, Korean, and other languages.
• Vector Graphics: Ability to draw lines, ovals, rectangles, and curves.
• Image Support: Draw JPG and PNG images, including setting image masks.
• Security: Password protection for PDF files.
• Typography: Supports font kerning and various text alignments (left, center, right, justify).
• Advanced Text: Support for superscript, subscript, and color models (RGB and CMYK).

Install the gopdf package using go get:

go get -u github.com/signintech/gopdf

To print text, initialize a gopdf.GoPdf instance, start it with a gopdf.Config (e.g., *gopdf.PageSizeA4), add a page, add a TTF font using AddTTFFont, set the font with SetFont, and use Cell to write text.

package main
import (
	"log"
	"github.com/signintech/gopdf"
)

func main() {
	pdf := gopdf.GoPdf{}
	pdf.Start(gopdf.Config{ PageSize: *gopdf.PageSizeA4 })
	pdf.AddPage()
	err := pdf.AddTTFFont("wts11", "../ttf/wts11.ttf")
	if err != nil {
		log.Print(err.Error())
		return
	}

	err = pdf.SetFont("wts11", "", 14)
	if err != nil {
		log.Print(err.Error())
		return
	}
	pdf.Cell(nil, "您好")
	pdf.WritePdf("hello.pdf")
}

You can import pages from an existing PDF file using pdf.ImportPage(filename, page_number, box_type). The imported page is returned as a template which can then be drawn onto the current document using pdf.UseImportedTemplate(template, x, y, w, h). Note: This functionality relies on the gofpdi package logic.

// Import page 1
tpl1 := pdf.ImportPage("example-pdf.pdf", 1, "/MediaBox")

// Draw imported template onto current page
pdf.UseImportedTemplate(tpl1, 50, 100, 400, 0)

Configure password protection during pdf.Start() using gopdf.PDFProtectionConfig. You can specify permissions (e.g., PermissionsPrint, PermissionsCopy, PermissionsModify) and set both OwnerPass and UserPass as byte slices.

pdf.Start(gopdf.Config{
    PageSize: *gopdf.PageSizeA4,
    Protection: gopdf.PDFProtectionConfig{
        UseProtection: true,
        Permissions: gopdf.PermissionsPrint | gopdf.PermissionsCopy | gopdf.PermissionsModify,
        OwnerPass:   []byte("123456"),
        UserPass:    []byte("123456789")
    },
})

To add links to a PDF:

• External Links: Use pdf.AddExternalLink(url, x, y, w, h) to create a clickable area over text.
• Internal Links (Anchors):
  1. Define an anchor using pdf.SetAnchor("name") at the target location.
  2. Create the link using pdf.AddInternalLink("name", x, y, w, h) at the source location.

// External link
pdf.Text("Link to example.com")
pdf.AddExternalLink("http://example.com/", 27.5, 28, 125, 15)

// Internal link
pdf.Text("Link to second page")
pdf.AddInternalLink("anchor", 27.5, 58, 120, 15)

// Target anchor
pdf.SetXY(30, 100)
pdf.SetAnchor("anchor")
pdf.Text("Anchor position")

Use pdf.Rotate(angle, x, y) to rotate the coordinate system around a point, then draw your content. Always call pdf.RotateReset() to return to the original orientation.

pdf.SetXY(100, 100)
pdf.Rotate(270.0, 100.0, 100.0)
pdf.Text("Hello...")
pdf.RotateReset()

If you need to print text that depends on information not known until the end of the document (like total page count), use the placeholder system:

1. Create a placeholder: pdf.PlaceHolderText(id, size).
2. Fill the placeholder: pdf.FillInPlaceHoldText(id, text, alignment) (where alignment is Left, Center, or Right).

Use SetFontWithStyle to apply gopdf.Superscript or gopdf.Subscript. The glyph size and baseline shift are derived from the font's metrics, while the logical font size maintains the line layout.

pdf.SetFont("font", "", 14)
pdf.Cell(nil, "E = mc")
pdf.SetFontWithStyle("font", gopdf.Superscript, 14)
pdf.Cell(nil, "2")
pdf.SetFontWithStyle("font", gopdf.Regular, 14)
pdf.Cell(nil, ", said Einstein")