pdfapi

package
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 Go to latest Published: Dec 12, 2020 License: BSD-3-Clause Imports: 12 Imported by: 0

Documentation

Overview

Package pdfapi will implement a low-level API for the PDF format.

The original package is by Ross Light (zombiezen). I copied it, rather than importing it, because I intend to write a low level PDF API from scratch and will use Ross's code as a loose reference.

There are other PDF packages around (most notably gofpdf (/github.com/jung-kurt/gofpdf) and gopdf (/github.com/signintech/gopdf). However, for my purpose these a often too high-level. Ross's package is the most concise of all and has a Go-like API (in contrast to, e.g., gofpdf).

My focus for the PDF API will be on concurrency, Unicode typesetting and the usage of PDF fragment templates.

Status

This is just a bag of ideas. Nothing useful for anyone else yet.

License

The original code has a BSD 2-clause license. Changes are published under a BSD 3-clause licencse. Please refer to the license file for details.

PDF Format

The PDF format can roughly be broken into four parts:

  • Header
  • List of Objects (with Streams)
  • XRef
  • Trailer

This package will stick closely to the nomenclature of PDF where possible.

Index

Constants

View Source 
const (
	Courier            = "Courier"
	CourierBold        = "Courier-Bold"
	CourierOblique     = "Courier-Oblique"
	CourierBoldOblique = "Courier-BoldOblique"

	Helvetica            = "Helvetica"
	HelveticaBold        = "Helvetica-Bold"
	HelveticaOblique     = "Helvetica-Oblique"
	HelveticaBoldOblique = "Helvetica-BoldOblique"

	Symbol = "Symbol"

	Times           = "Times-Roman"
	TimesBold       = "Times-Bold"
	TimesItalic     = "Times-Italic"
	TimesBoldItalic = "Times-BoldItalic"

	ZapfDingbats = "ZapfDingbats"
)

Standard 14 fonts

View Source 
const (
	Newline = "\n" //Newline = "\r\n"

)

Variables

This section is empty.

Functions

func Deg2Rad 

func Deg2Rad(theta float32) float32

Deg2Rad returns degree angle coordinates to radians.

Types

type Canvas 

type Canvas struct {
	// contains filtered or unexported fields
}

Canvas is a two-dimensional drawing region on a single page. You can obtain a canvas once you have created a document.

func (*Canvas) Close 

func (canvas *Canvas) Close() error

Close flushes the page's stream to the document. This must be called once drawing has completed or else the document will be inconsistent.

func (*Canvas) CropBox 

func (canvas *Canvas) CropBox() Rectangle

CropBox returns the page's crop box.

func (*Canvas) Document 

func (canvas *Canvas) Document() *Document

Document returns the document the canvas is attached to.

func (*Canvas) DrawImage 

func (canvas *Canvas) DrawImage(img image.Image, rect Rectangle)

DrawImage paints a raster image at the given location and scaled to the given dimensions. If you want to render the same image multiple times in the same document, use DrawImageReference.

func (*Canvas) DrawImageReference 

func (canvas *Canvas) DrawImageReference(ref Reference, rect Rectangle)

DrawImageReference paints the raster image referenced in the document at the given location and scaled to the given dimensions.

func (*Canvas) DrawLine 

func (canvas *Canvas) DrawLine(pt1, pt2 Point)

DrawLine paints a straight line from pt1 to pt2 using the current stroke color and line width.

func (*Canvas) DrawText 

func (canvas *Canvas) DrawText(text *Text)

DrawText paints a text object onto the canvas.

func (*Canvas) Fill 

func (canvas *Canvas) Fill(p *Path)

Fill paints the area enclosed by the given path using the current fill color.

func (*Canvas) FillStroke 

func (canvas *Canvas) FillStroke(p *Path)

FillStroke fills then strokes the given path. This operation has the same effect as performing a fill then a stroke, but does not repeat the path in the file.

func (*Canvas) MoveTo 

func (canvas *Canvas) MoveTo(pt Point)

func (*Canvas) PopState 

func (canvas *Canvas) PopState()

PopState restores the most recently saved graphics state by popping it from the stack.

func (*Canvas) PushState 

func (canvas *Canvas) PushState()

PushState saves a copy of the current graphics state. The state can later be restored using Pop.

func (*Canvas) SetFillColor 

func (canvas *Canvas) SetFillColor(c color.Color)

SetFillColor changes the current fill color to the given RGB triple (in device RGB space).

func (*Canvas) SetLineDash 

func (canvas *Canvas) SetLineDash(phase Unit, dash []Unit)

SetLineDash changes the line dash pattern in the current graphics state. Examples: 

c.SetLineDash(0, []Unit{})     // solid line
c.SetLineDash(0, []Unit{3})    // 3 units on, 3 units off...
c.SetLineDash(0, []Unit{2, 1}) // 2 units on, 1 unit off...
c.SetLineDash(1, []Unit{2})    // 1 unit on, 2 units off, 2 units on...

func (*Canvas) SetLineWidth 

func (canvas *Canvas) SetLineWidth(w Unit)

SetLineWidth changes the stroke width to the given value.

func (*Canvas) SetStrokeColor 

func (canvas *Canvas) SetStrokeColor(c color.Color)

SetStrokeColor changes the current stroke color to the given RGB triple (in device RGB space).

func (*Canvas) Size 

func (canvas *Canvas) Size() (width, height Unit)

Size returns the page's media box (the size of the physical medium).

func (*Canvas) Stroke 

func (canvas *Canvas) Stroke(p *Path)

Stroke paints a line along the given path using the current stroke color.

func (*Canvas) Transform 

func (canvas *Canvas) Transform(t Transform)

Transform concatenates a 3x3 matrix with the current transformation matrix. See type Transform.

type Document 

type Document struct {
	// contains filtered or unexported fields
}

Document provides a high-level drawing interface for the PDF format.

func NewDocument 

func NewDocument() *Document

New creates a new document with no pages.

func (*Document) AddImage 

func (doc *Document) AddImage(img image.Image) Reference

AddImage encodes an image into the document's stream and returns its PDF file reference. This reference can be used to draw the image multiple times without storing the image multiple times.

func (*Document) Assemble 

func (doc *Document) Assemble(c *Canvas)

Assemble takes a page and integrates it into the document's structure.

func (*Document) Encode 

func (doc *Document) Encode(w io.Writer) error

Encode writes the document to a writer in the PDF format.

func (*Document) NewPage 

func (doc *Document) NewPage(width, height Unit) *Canvas

NewPage creates a new canvas with the given dimensions. TODO: do not directly couple to document TODO de-couple page geometry from document geometry

type Font 

type Font struct {
	Name string
	// contains filtered or unexported fields
}

Font is a type representing fonts in PDF documents.

func NewInternalFont 

func NewInternalFont(fname string) *Font

NewInternalFont creates a font for one of the PDF standard fonts, given a font's name (e.g., "Helveltica").

func (*Font) String 

func (fn *Font) String() string

String returns the Font's indentifier string.

type FontFormat 

type FontFormat int8
const (
	Standard FontFormat
	Type1
	Type3
	TrueType_Mac
	TrueType_Win
	OpenType
	WOFF
	WOFF2
)

type Path 

type Path struct {
	// contains filtered or unexported fields
}

Path is a shape that can be painted on a canvas. The zero value is an empty path.

func (*Path) Close 

func (path *Path) Close()

Close appends a line segment from the current point to the starting point of the subpath.

func (*Path) CurveTo 

func (path *Path) CurveTo(pt1, pt2, pt3 Point)

Curve appends a cubic Bezier curve to the path.

func (*Path) Line 

func (path *Path) Line(pt Point)

Line appends a line segment from the current point to the given location.

func (*Path) LineTo 

func (path *Path) LineTo(pt Point)

Line appends a line segment from the current point to the given location.

func (*Path) Move 

func (path *Path) Move(pt Point)

Move begins a new subpath by moving the current point by a vector.

func (*Path) MoveTo 

func (path *Path) MoveTo(pt Point)

MoveTo begins a new subpath by moving the current point to the given location.

func (*Path) Rectangle 

func (path *Path) Rectangle(rect Rectangle, corner Unit)

Rectangle appends a complete rectangle to the path. If corner > 0, the corners of the rectangle will be rounded. All four corners will have the same radius.

type Point 

type Point struct {
	X, Y Unit
}

Point is a 2D point.

type Rectangle 

type Rectangle struct {
	Min, Max Point
}

A Rectangle defines a rectangle with two points.

func (Rectangle) Dx 

func (r Rectangle) Dx() Unit

Dx returns the rectangle's width.

func (Rectangle) Dy 

func (r Rectangle) Dy() Unit

Dy returns the rectangle's height.

type Reference 

type Reference struct {
	Number     uint
	Generation uint
}

Reference holds a PDF indirect reference.

type Text 

type Text struct {
	// contains filtered or unexported fields
}

Text is a PDF text object. The zero value is an empty text object.

func (*Text) AddGlyphs 

func (text *Text) AddGlyphs(s string)

Text adds a string to the text object.

func (*Text) AdvanceCursor 

func (text *Text) AdvanceCursor(x Unit)

AdvanceCursor moves the text cursor in x-direction.

func (*Text) Cursor 

func (text *Text) Cursor() Point

Cursor returns the current cursor location. This is where new glyphs will be positioned.

func (*Text) MoveCursor 

func (text *Text) MoveCursor(diff Point)

MoveCursor moves the text cursor by a vector.

func (*Text) MoveCursorTo 

func (text *Text) MoveCursorTo(pt Point)

MoveCursorTo moves the text cursor to a point.

func (*Text) SetFont 

func (text *Text) SetFont(font *Font, size Unit)

SetFont changes the current font to a standard font.

type Transform 

type Transform [6]float32

Transform represents an affine transformation (on a PDF graphics state). The six indices map to values in a 3x3-matrix as shown below: 

⎛ a b 0 ⎞
⎜ c d 0 ⎥
⎝ e f 1 ⎠

For more information, see Section 8.3.4 of ISO 32000-1.

func Identity 

func Identity() Transform

Identity is the neutral transformation. This is the starting point for chaining transform operations. To create a transformation which shifts a point by vector (a, b) and then rotates around origin by 30 degrees: 

vector := Point{a, b}
T := Identity().Shifted(vector).Rotated(Deg2Rad(30))
mycanvas.Transform(T)

func (Transform) Rotated 

func (t Transform) Rotated(theta float32) Transform

Rotate rotates the canvas's coordinate system by a given angle (in radians), counterclockwise.

func (Transform) Scaled 

func (t Transform) Scaled(x, y float32) Transform

Scale multiplies the canvas's coordinate system by the given scalars.

func (Transform) Shifted 

func (t Transform) Shifted(by Point) Transform

Shifted moves the canvas's coordinates system by the given offset.

type Unit 

type Unit float32

Unit is a device-independent dimensional type. On a new canvas, this represents 1/72 of an inch. 

const (
	Pt   Unit = 1
	Inch Unit = 72
	Cm   Unit = 28.35
)

Common unit scales 

const (
	USLetterWidth  Unit = 8.5 * Inch
	USLetterHeight Unit = 11.0 * Inch

	A4Width  Unit = 21.0 * Cm
	A4Height Unit = 29.7 * Cm
)

Common page sizes

func (Unit) String 

func (unit Unit) String() string

Source Files

View all Source files

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