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Go code (golang) to create PDF documents with several layers of abstraction that allow both, easy placement of elements on pages and accessing lower layers to implement any type of PDF object / operator.
Does support Composite Fonts for full Unicode support.
The highest level of abstraction is provided by the gopdf package. Simply create a new Builder object, add pages and add elements to the pages:
package yours
import (
"github.com/raceresult/gopdf"
"github.com/raceresult/gopdf/types"
)
func TestExample1(t *testing.T) {
// create new PDF Builder
pb := gopdf.New()
// use a built-in standard fontm
f, err := pb.NewStandardFont(types.StandardFont_Helvetica, types.EncodingWinAnsi)
if err != nil {
t.Error(err)
return
}
// add first page
p := pb.NewPage(gopdf.GetStandardPageSize(gopdf.PageSizeA4, false))
// add "hello world" element
p.AddElement(&gopdf.TextElement{
TextChunk: gopdf.TextChunk{
Text: "hello world",
Font: f,
FontSize: 36,
},
Left: gopdf.MM(105),
Top: gopdf.MM(100),
TextAlign: gopdf.HorizontalAlignCenter,
})
// output
bts, err := pb.Build()
...
}More advanced: let's add an image, a rectangle and a text using a composite font. Using a composite font, any unicode character can be mapped to any glyph in one or more fonts. Non-composite fonts, on the contrary, only support 256 different characters, so in a world of UTF-8/Unicode, composite fonts are the only thing you want to use. Character encoding and subsetting (embed fonts reduced to only those characters you are using) is quite sophisticated but completely handled by the pdf package. When using Composite Fonts you only need to handover normal (UTF-8 encoded) Go strings.
package yours
import (
"github.com/raceresult/gopdf/builder"
"github.com/raceresult/gopdf/types"
)
func TestExample2(t *testing.T) {
// create new PDF Builder
pb := gopdf.New()
// add first page
p := pb.NewPage(gopdf.GetStandardPageSize(gopdf.PageSizeA4, false))
// add image
bts, err := ioutil.ReadFile("myImage.jpg")
if err != nil {
t.Error(err)
return
}
img, err := pb.NewImage(bts)
if err != nil {
t.Error(err)
return
}
p.AddElement(&gopdf.ImageElement{
Width: gopdf.MM(70),
Height: gopdf.MM(70 * float64(img.Image.Height) / float64(img.Image.Width)),
Left: gopdf.MM(20),
Top: gopdf.MM(20),
Img: img,
})
// add rectangle
p.AddElement(&gopdf.TextElement{
TextChunk: gopdf.TextChunk{
Text: "hello world - 漢語",
Font: f,
FontSize: 36,
Color: gopdf.NewColorRGB(200, 200, 200),
OutlineColor: gopdf.NewColorRGB(10, 20, 10),
OutlineWidth: gopdf.MM(0.5),
},
Left: gopdf.MM(20),
Top: gopdf.MM(100),
})
// add composite font
bts, err = ioutil.ReadFile("arialuni.ttf")
if err != nil {
t.Error(err)
return
}
f, err := pb.NewCompositeFont(bts)
if err != nil {
t.Error(err)
return
}
// add text using composite font
p.AddElement(&gopdf.TextElement{
Text: "hello world - 漢語",
Font: f,
FontSize: 36,
Left: gopdf.MM(20),
Top: gopdf.MM(100),
Color: gopdf.ColorRGB{200, 200, 200},
OutlineColor: gopdf.ColorRGB{10, 20, 10},
OutlineWidth: gopdf.MM(0.5),
})
// output
bts, err := pb.Build()
...
}This way, the builder supports the following element types with various attributes:
- images (supports jpg, png, gif, bmp)
- lines
- rectangles (filled or unfilled)
- texts
- textboxes (text with max width, opt. max height, word wrap, ..)
The following section describes how to go one level deeper and add custom functionality that is not yet provided by the builder package.
First of all, a quick overview of the PDF file format: PDF files are a set of "objects" that are referenced by other objects. For example, the root is the "Document Catalog" which references to the "Page Tree" which references to the individual page objects. Each page references to resources like images or fonts, and also to a "Content Stream" that contains the commands to draw text, images, or graphical elements.
The content stream is a list of "Operators" with "Operands", you could also call them function calls. Some functions change a state, for example set the drawing position or change the drawing color, others actually draw the text/image/line/...
Please take a look at the PDF Reference manual. You may have to use it look up the functions you need to use for your needs.
Let's assume you need a custom function to draw a cubic Bézier curve. The operators for this are:
- "m": move to position
- "c": add bezier curve to current path line
- "S": stroke the path line.
Most operators have been implemented in the package "pdf" (even if there are no elements in the builder package using them). In this example, the functions needed are:
func (q *Page) Path_m(x, y float64)
func (q *Page) Path_c(x1, y1, x2, y2, x3, y3 float64)
func (q *Page) Path_S()You can easily create your own element type for the Builder, it only needs to fulfill the Element interface:
type Element interface {
Build(page *pdf.Page)
}For example:
type BezierCurve struct {
X, Y Length
X1, Y1, X2, Y2, X3, Y3 Length
}
func (q *BezierCurve) Build(page *pdf.Page) error {
page.Path_m(q.X.Pt(), q.Y.Pt())
page.Path_c(q.X1.Pt(), q.Y1.Pt(), q.X2.Pt(), q.Y2.Pt(), q.X3.Pt(), q.Y3.Pt())
page.Path_S()
return nil
}An instance of BezierCurve can now be added to a page using the AddElement method.
If you need to use operators that are not implemented in the pdf package, you can use the general function AddCommand:
func (q *Page) AddCommand(operator string, args ...types.Object)If, however, the operator is implemented, please use the associated function to avoid unexpected behavior. In order to minimize the size of the PDF file, the pdf package keeps tracking of the current text and graphics state and ignores function call, that would not change the state, for example:
func (q *Page) TextState_Tc(charSpace float64) {
if q.textState.Tc == charSpace {
return
}
q.textState.Tc = charSpace
q.AddCommand("Tc", types.Int(charSpace))
}If you would call AddCommand("Tc", ...) instead of TextState_Tc, the internal textState would not be updated and you may see unexpected behavior later in your program.
To install GoPDF, use go get:
go get github.com/raceresult/gopdf
To update GoPDF to the latest version, use go get -u github.com/raceresult/gopdf.
We currently support the most recent major Go versions from 1.16 onward.
Please feel free to submit issues, fork the repository and send pull requests!
When submitting an issue, we ask that you please include a complete test function that demonstrates the issue.
This project is licensed under the terms of the MIT license.