ps

Overview ¶

Package ps implements the PostScript backend for libcairo rendering.

EPS ¶

EPS files must contain only one page.

Note that libcairo does not include the device independent preview.

The Encapsulated PostScript Specfication† describes how to embed EPS files into PostScript files

† https://partners.adobe.com/public/developer/en/ps/5002.EPSF_Spec.pdf

Fonts ¶

The PostScript surface natively supports Type 1 and TrueType fonts. All other font types (including OpenType/PS) are converted to Type 1.

Fonts are always subsetted and embedded.

Fallback images ¶

Cairo will ensure that the PostScript output looks the same as an image surface for the same set of operations. When cairo drawing operations are performed that cannot be represented natively in PostScript, the drawing is rasterized and embedded in the output.

The rasterization of unsupported operations is limited to the smallest rectangle, or set of rectangles, required to draw the unsupported operations.

Fallback images are the main cause of large file sizes and slow printing times. Fallback images have a comment containing the size and location of the fallback.

> grep 'Fallback' output.ps
output.ps:% Fallback Image: x=100, y=100, w=299, h=50 res=300dpi size=783750
output.ps:% Fallback Image: x=100, y=150, w=350, h=250 res=300dpi size=4560834
output.ps:% Fallback Image: x=150, y=400, w=299, h=50 res=300dpi size=783750

Supported Features ¶

The following tables lists all features natively supported by the PostScript surface.

FEATURE                          NOTES
Paint/Fill/Stroke/ShowGlyphs     depending on pattern
Fonts                            some may be converted to Type 1
Opaque colors
Images
Linear gradients                 level 3 only
Radial gradients                 level 3 and when one circle is inside
                                 the other and extent is ExtendNone or
                                 ExtendPad only.
PushGroup/CreateSimilar
OpSource
OpOver

Requirements ¶

Libcairo must be compiled with

CAIRO_HAS_PS_SURFACE

in addition to the requirements of cairo.

draw := func(c *cairo.Context, text string, width, height int) error {
	const Border = 50
	border := cairo.Pt(Border, Border)
	size := cairo.Pt(float64(width), float64(height))

	c.
		Rectangle(cairo.Rectangle{border, border.Sub(size)}).
		SetLineWidth(2).
		Stroke()

	c.
		SelectFont("Sans", 0, 0).
		SetFontSize(60).
		MoveTo(cairo.Pt(200, float64(height)/3)).
		ShowText(text)

	c.
		SetFontSize(18).
		MoveTo(cairo.Pt(120, float64(height)*2/3.)).
		ShowText(fmt.Sprintf("Width: %d points\t\tHeight: %d points"))

	return nil
}

//A4
const (
	PageWidth  = 595
	PageHeight = 842
)
surface, err := New(os.Stdout, PageWidth, PageHeight, false, nil, nil)
if err != nil {
	log.Println(err)
	return
}
defer surface.Close()

c, err := cairo.New(surface)
if err != nil {
	log.Println(err)
	return
}
defer c.Close()

//Print portrait page
surface.AddComment("PageOrientation", "Portrait")
err = draw(c, "Portrait", PageWidth, PageHeight)
if err != nil {
	log.Println(err)
	return
}
surface.ShowPage()

//Print landscape page
surface.AddComment("PageOrientation", "Landscape")

//Move the origin to landscape origin and rotate counterclockwise
c.
	Translate(cairo.Pt(0, PageHeight)).
	Rotate(-math.Pi / 2)

err = draw(c, "Landscape", PageHeight, PageWidth)
if err != nil {
	log.Println(err)
	return
}
surface.ShowPage()

Output: