#SVGo: A Go library for SVG generation#

The library generates SVG as defined by the Scalable Vector Graphics 1.1 Specification (http://www.w3.org/TR/SVG11/). Output goes to the specified io.Writer.

Supported SVG elements and functions

Shapes, lines, text

circle, ellipse, polygon, polyline, rect (including roundrects), line, text

Paths

general, arc, cubic and quadratic bezier paths,

Image and Gradients

image, linearGradient, radialGradient,

Transforms

translate, rotate, scale, skewX, skewY

Filter Effects

filter, feBlend, feColorMatrix, feColorMatrix, feComponentTransfer, feComposite, feConvolveMatrix, feDiffuseLighting, feDisplacementMap, feDistantLight, feFlood, feGaussianBlur, feImage, feMerge, feMorphology, feOffset, fePointLight, feSpecularLighting, feSpotLight,feTile, feTurbulence

Metadata elements

desc, defs, g (style, transform, id), marker, mask, pattern, title, (a)ddress, link, script, use

Building and Usage

See svgdef.[svg|png|pdf] for a graphical view of the function calls

Usage: (assuming GOPATH is set)

go get github.com/ajstarks/svgo
go install github.com/ajstarks/svgo/...

You can use godoc to browse the documentation from the command line:

$ go doc github.com/ajstarks/svgo

a minimal program, to generate SVG to standard output.

package main

import (
	"github.com/ajstarks/svgo"
	"os"
)

func main() {
	width := 500
	height := 500
	canvas := svg.New(os.Stdout)
	canvas.Start(width, height)
	canvas.Circle(width/2, height/2, 100)
	canvas.Text(width/2, height/2, "Hello, SVG", "text-anchor:middle;font-size:30px;fill:white")
	canvas.End()
}

Drawing in a web server: (http://localhost:2003/circle)

package main

import (
	"log"
	"github.com/ajstarks/svgo"
	"net/http"
)

func main() {
	http.Handle("/circle", http.HandlerFunc(circle))
	err := http.ListenAndServe(":2003", nil)
	if err != nil {
		log.Fatal("ListenAndServe:", err)
	}
}

func circle(w http.ResponseWriter, req *http.Request) {
  w.Header().Set("Content-Type", "image/svg+xml")
  s := svg.New(w)
  s.Start(500, 500)
  s.Circle(250, 250, 125, "fill:none;stroke:black")
  s.End()
}

You may view the SVG output with a browser that supports SVG (tested on Chrome, Opera, Firefox and Safari), or any other SVG user-agent such as Batik Squiggle.

Graphics Sketching with SVGo and svgplay

Combined with the svgplay command, SVGo can be used to "sketch" with code in a browser.

To use svgplay and SVGo, first go to a directory with your code, and run:

$ svgplay
2014/06/25 22:05:28 ☠ ☠ ☠ Warning: this server allows a client connecting to 127.0.0.1:1999 to execute code on this computer ☠ ☠ ☠	

Next open your browser to the svgplay server you just started. svgplay only listens on localhost, and uses port 1999 (guess which year SVG was first introduced) by default

http://localhost:1999/

Enter your code in the textarea, and when you are ready to run press Shift--Enter. The code will be compiled, with the results on the right. To update, change the code and repeat. Note that compilation errors are shown in red under the code. In order for svgplay/SVGo to work, make sure that the io.Writer specified with the New function is os.Stdout.

If you want to sketch with an existing file, enter its URL:

http://localhost:1999/foo.go

SVGo Papers and presentations

• SVGo paper from SVGOpen 2011 http://www.svgopen.org/2011/papers/34-SVGo_a_Go_Library_for_SVG_generation

• Programming Pictures with SVGo https://speakerdeck.com/u/ajstarks/p/programming-pictures-with-svgo

• SVGo Workshop https://speakerdeck.com/u/ajstarks/p/svgo-workshop

Tutorial Video

A video describing how to use the package can be seen on YouTube at http://www.youtube.com/watch?v=ze6O2Dj5gQ4

Package contents

• svg.go: Library
• newsvg: Coding template command
• svgdef: Creates a SVG representation of the API
• android: The Android logo
• bubtrail: Bubble trails
• bulletgraph: Bullet Graphs (via Stephen Few)
• colortab: Display SVG named colors with RGB values
• compx: Component diagrams
• flower: Random "flowers"
• fontcompare: Compare two fonts
• f50: Get 50 photos from Flickr based on a query
• fe: Filter effects
• funnel: Funnel from transparent circles
• gradient: Linear and radial gradients
• html5logo: HTML5 logo with draggable elements
• imfade: Show image fading
• lewitt: Version of Sol Lewitt's Wall Drawing 91
• ltr: Layer Tennis Remixes
• marker: Test markers
• paths: Demonstrate SVG paths
• pattern: Test patterns
• planets: Show the scale of the Solar system
• pmap: Proportion maps
• randcomp: Compare random number generators
• richter: Gerhard Richter's 256 colors
• rl: Random lines (port of a Processing demo)
• skewabc: Skew ABC
• stockproduct: Visualize product and stock prices
• svgopher: SVGo Mascot
• svgplay: SVGo sketching server
• svgplot: Plot data
• svgrid: Compose SVG files in a grid
• tsg: Twitter Search Grid
• tumblrgrid: Tumblr picture grid
• turbulence: Turbulence filter effect
• vismem: Visualize data from files
• webfonts: "Hello, World" with Google Web Fonts
• websvg: Generate SVG as a web server

Functions and types

Many functions use x, y to specify an object's location, and w, h to specify the object's width and height. Where applicable, a final optional argument specifies the style to be applied to the object. The style strings follow the SVG standard; name:value pairs delimited by semicolons, or a series of name="value" pairs. For example: "fill:none; opacity:0.3" or fill="none" opacity="0.3" (see: http://www.w3.org/TR/SVG11/styling.html)

The SVG type:

type SVG struct {
    Writer   io.Writer
}

Most operations are methods on this type, specifying the destination io.Writer.

The Offcolor type:

type Offcolor struct {
	Offset  uint8
	Color   string
	Opacity float64
}

is used to specify the offset, color, and opacity of stop colors in linear and radial gradients

The Filterspec type:

type Filterspec struct {
	In string
	In2 string
	Result string
}

is used to specify inputs and results for filter effects

Structure, Scripting, Metadata, Transformation and Links

New(w io.Writer) *SVG

Constructor, Specify the output destination.

Start(w int, h int, attributes ...string)

begin the SVG document with the width w and height h. Optionally add additional elements (such as additional namespaces or scripting events) http://www.w3.org/TR/SVG11/struct.html#SVGElement

Startview(w, h, minx, miny, vw, vh int)

begin the SVG document with the width w, height h, with a viewBox at minx, miny, vw, vh. http://www.w3.org/TR/SVG11/struct.html#SVGElement

Startunit(w int, h int, unit string, ns ...string)

begin the SVG document, with width and height in the specified units. Optionally add additional elements (such as additional namespaces or scripting events) http://www.w3.org/TR/SVG11/struct.html#SVGElement

Startpercent(w int, h int, ns ...string)

begin the SVG document, with width and height in percent. Optionally add additional elements (such as additional namespaces or scripting events) http://www.w3.org/TR/SVG11/struct.html#SVGElement

StartviewUnit(w, h int, unit string, minx, miny, vw, vh int)

begin the SVG document with the width w, height h, in the specified unit, with a viewBox at minx, miny, vw, vh. http://www.w3.org/TR/SVG11/struct.html#SVGElement

End()

end the SVG document

Script(scriptype string, data ...string)

Script defines a script with a specified type, (for example "application/javascript"). if the first variadic argument is a link, use only the link reference. Otherwise, treat variadic arguments as the text of the script (marked up as CDATA). if no data is specified, simply close the script element. http://www.w3.org/TR/SVG/script.html

Group(s ...string)

begin a group, with arbitrary attributes http://www.w3.org/TR/SVG11/struct.html#GElement

Gstyle(s string)

begin a group, with the specified style. http://www.w3.org/TR/SVG11/struct.html#GElement

Gid(s string)

begin a group, with the specified id.

Gtransform(s string)

begin a group, with the specified transform, end with Gend(). http://www.w3.org/TR/SVG11/coords.html#TransformAttribute

Translate(x, y int)

begins coordinate translation to (x,y), end with Gend(). http://www.w3.org/TR/SVG11/coords.html#TransformAttribute

Scale(n float64)

scales the coordinate system by n, end with Gend(). http://www.w3.org/TR/SVG11/coords.html#TransformAttribute

ScaleXY(x, y float64)

scales the coordinate system by x, y. End with Gend(). http://www.w3.org/TR/SVG11/coords.html#TransformAttribute

SkewX(a float64)

SkewX skews the x coordinate system by angle a, end with Gend(). http://www.w3.org/TR/SVG11/coords.html#TransformAttribute

SkewY(a float64)

SkewY skews the y coordinate system by angle a, end with Gend(). http://www.w3.org/TR/SVG11/coords.html#TransformAttribute

SkewXY(ax, ay float64)

SkewXY skews x and y coordinate systems by ax, ay respectively, end with Gend(). http://www.w3.org/TR/SVG11/coords.html#TransformAttribute

Rotate(r float64)

rotates the coordinate system by r degrees, end with Gend(). http://www.w3.org/TR/SVG11/coords.html#TransformAttribute

TranslateRotate(x, y int, r float64)

translates the coordinate system to (x,y), then rotates to r degrees, end with Gend().

RotateTranslate(x, y int, r float64)

rotates the coordinate system r degrees, then translates to (x,y), end with Gend().

Gend()

end the group (must be paired with Gstyle, Gtransform, Gid).

ClipPath(s ...string)

Begin a ClipPath http://www.w3.org/TR/SVG/masking.html#ClippingPaths

ClipEnd()

End a ClipPath http://www.w3.org/TR/SVG/masking.html#ClippingPaths

Def()

begin a definition block. http://www.w3.org/TR/SVG11/struct.html#DefsElement

DefEnd()

end a definition block.

Marker(id string, x, y, w, h int, s ...string)

define a marker http://www.w3.org/TR/SVG11/painting.html#MarkerElement

MarkerEnd()

end a marker

Mask(id string, x int, y int, w int, h int, s ...string)

creates a mask with a specified id, dimension, and optional style. http://www.w3.org/TR/SVG/masking.html

MaskEnd()

ends the Mask element.

Pattern(id string, x, y, width, height int, putype string, s ...string)

define a Pattern with the specified dimensions, the putype can be either "user" or "obj", which sets the patternUnits attribute to be either userSpaceOnUse or objectBoundingBox. http://www.w3.org/TR/SVG11/pservers.html#Patterns

Desc(s string)

specify the text of the description. http://www.w3.org/TR/SVG11/struct.html#DescElement

Title(s string)

specify the text of the title. http://www.w3.org/TR/SVG11/struct.html#TitleElement

Link(href string, title string)

begin a link named "href", with the specified title. http://www.w3.org/TR/SVG11/linking.html#Links

LinkEnd()

end the link.

Use(x int, y int, link string, s ...string)

place the object referenced at link at the location x, y. http://www.w3.org/TR/SVG11/struct.html#UseElement

Shapes

Circle(x int, y int, r int, s ...string)

draw a circle, centered at x,y with radius r. http://www.w3.org/TR/SVG11/shapes.html#CircleElement

Ellipse(x int, y int, w int, h int, s ...string)

draw an ellipse, centered at x,y with radii w, and h. http://www.w3.org/TR/SVG11/shapes.html#EllipseElement

Polygon(x []int, y []int, s ...string)

draw a series of line segments using an array of x, y coordinates. http://www.w3.org/TR/SVG11/shapes.html#PolygonElement

Rect(x int, y int, w int, h int, s ...string)

draw a rectangle with upper left-hand corner at x,y, with width w, and height h. http://www.w3.org/TR/SVG11/shapes.html#RectElement

CenterRect(x int, y int, w int, h int, s ...string)

draw a rectangle with its center at x,y, with width w, and height h.

Roundrect(x int, y int, w int, h int, rx int, ry int, s ...string)

draw a rounded rectangle with upper the left-hand corner at x,y, with width w, and height h. The radii for the rounded portion is specified by rx (width), and ry (height).

Square(x int, y int, s int, style ...string)

draw a square with upper left corner at x,y with sides of length s.

Paths

Path(p string, s ...style)

draw the arbitrary path as specified in p, according to the style specified in s. http://www.w3.org/TR/SVG11/paths.html

Arc(sx int, sy int, ax int, ay int, r int, large bool, sweep bool, ex int, ey int, s ...string)

draw an elliptical arc beginning coordinate at sx,sy, ending coordinate at ex, ey width and height of the arc are specified by ax, ay, the x axis rotation is r

if sweep is true, then the arc will be drawn in a "positive-angle" direction (clockwise), if false, the arc is drawn counterclockwise.

if large is true, the arc sweep angle is greater than or equal to 180 degrees, otherwise the arc sweep is less than 180 degrees. http://www.w3.org/TR/SVG11/paths.html#PathDataEllipticalArcCommands

Bezier(sx int, sy int, cx int, cy int, px int, py int, ex int, ey int, s ...string)

draw a cubic bezier curve, beginning at sx,sy, ending at ex,ey with control points at cx,cy and px,py. http://www.w3.org/TR/SVG11/paths.html#PathDataCubicBezierCommands

Qbezier(sx int, sy int, cx int, cy int, ex int, ey int, tx int, ty int, s ...string)

draw a quadratic bezier curve, beginning at sx, sy, ending at tx,ty with control points are at cx,cy, ex,ey. http://www.w3.org/TR/SVG11/paths.html#PathDataQuadraticBezierCommands

Qbez(sx int, sy int, cx int, cy int, ex int, ey int, s...string)

draws a quadratic bezier curver, with optional style beginning at sx,sy, ending at ex, sy with the control point at cx, cy. http://www.w3.org/TR/SVG11/paths.html#PathDataQuadraticBezierCommands

Lines

Line(x1 int, y1 int, x2 int, y2 int, s ...string)

draw a line segment between x1,y1 and x2,y2. http://www.w3.org/TR/SVG11/shapes.html#LineElement

Polyline(x []int, y []int, s ...string)

draw a polygon using coordinates specified in x,y arrays. http://www.w3.org/TR/SVG11/shapes.html#PolylineElement

Image and Text

Image(x int, y int, w int, h int, link string, s ...string)

place at x,y (upper left hand corner), the image with width w, and height h, referenced at link. http://www.w3.org/TR/SVG11/struct.html#ImageElement

Text(x int, y int, t string, s ...string)

Place the specified text, t at x,y according to the style specified in s. http://www.w3.org/TR/SVG11/text.html#TextElement

Textlines(x, y int, s []string, size, spacing int, fill, align string)

Places lines of text in s, starting at x,y, at the specified size, fill, and alignment, and spacing.

Textpath(t string, pathid string, s ...string)

places optionally styled text along a previously defined path. http://www.w3.org/TR/SVG11/text.html#TextPathElement

Color

RGB(r int, g int, b int) string

creates a style string for the fill color designated by the (r)ed, g(reen), (b)lue components. http://www.w3.org/TR/css3-color/

RGBA(r int, g int, b int, a float64) string

as above, but includes the color's opacity as a value between 0.0 (fully transparent) and 1.0 (opaque).

Gradients

LinearGradient(id string, x1, y1, x2, y2 uint8, sc []Offcolor)

constructs a linear color gradient identified by id, along the vector defined by (x1,y1), and (x2,y2). The stop color sequence defined in sc. Coordinates are expressed as percentages. http://www.w3.org/TR/SVG11/pservers.html#LinearGradients

RadialGradient(id string, cx, cy, r, fx, fy uint8, sc []Offcolor)

constructs a radial color gradient identified by id, centered at (cx,cy), with a radius of r. (fx, fy) define the location of the focal point of the light source. The stop color sequence defined in sc. Coordinates are expressed as percentages. http://www.w3.org/TR/SVG11/pservers.html#RadialGradients

Filter Effects

Filter(id string, s ...string)

Filter begins a filter set Standard reference: http://www.w3.org/TR/SVG11/filters.html#FilterElement

Fend() 

Fend ends a filter set Standard reference: http://www.w3.org/TR/SVG11/filters.html#FilterElement

FeBlend(fs Filterspec, mode string, s ...string) 

FeBlend specifies a Blend filter primitive Standard reference: http://www.w3.org/TR/SVG11/filters.html#feBlendElement

FeColorMatrix(fs Filterspec, values [20]float64, s ...string)	

FeColorMatrix specifies a color matrix filter primitive, with matrix values Standard reference: http://www.w3.org/TR/SVG11/filters.html#feColorMatrixElement

FeColorMatrixHue(fs Filterspec, value float64, s ...string)  	

FeColorMatrix specifies a color matrix filter primitive, with hue values Standard reference: http://www.w3.org/TR/SVG11/filters.html#feColorMatrixElement

FeColorMatrixSaturate(fs Filterspec, value float64, s ...string) 

FeColorMatrix specifies a color matrix filter primitive, with saturation values Standard reference: http://www.w3.org/TR/SVG11/filters.html#feColorMatrixElement

FeColorMatrixLuminence(fs Filterspec, s ...string) 

FeColorMatrix specifies a color matrix filter primitive, with luminence values Standard reference: http://www.w3.org/TR/SVG11/filters.html#feColorMatrixElement

FeComponentTransfer()  	

FeComponentTransfer begins a feComponent filter Element> Standard reference: http://www.w3.org/TR/SVG11/filters.html#feComponentTransferElement

FeCompEnd()

FeCompEnd ends a feComponent filter Element>

FeComposite(fs Filterspec, operator string, k1, k2, k3, k4 int, s ...string)

FeComposite specifies a feComposite filter primitive Standard reference: http://www.w3.org/TR/SVG11/filters.html#feCompositeElement

FeConvolveMatrix(fs Filterspec, matrix [9]int, s ...string)

FeConvolveMatrix specifies a feConvolveMatrix filter primitive Standard referencd: http://www.w3.org/TR/SVG11/filters.html#feConvolveMatrixElement

 FeDiffuseLighting(fs Filterspec, scale, constant float64, s ...string) 

FeDiffuseLighting specifies a diffuse lighting filter primitive, a container for light source Element>s, end with DiffuseEnd()

 FeDiffEnd()

FeDiffuseEnd ends a diffuse lighting filter primitive container Standard reference: http://www.w3.org/TR/SVG11/filters.html#feDiffuseLightingElement

 FeDisplacementMap(fs Filterspec, scale float64, xchannel, ychannel string, s ...string)

FeDisplacementMap specifies a feDisplacementMap filter primitive Standard reference: http://www.w3.org/TR/SVG11/filters.html#feDisplacementMapElement

 FeDistantLight(fs Filterspec, azimuth, elevation float64, s ...string)

FeDistantLight specifies a feDistantLight filter primitive Standard reference: http://www.w3.org/TR/SVG11/filters.html#feDistantLightElement

 FeFlood(fs Filterspec, color string, opacity float64, s ...string)

FeFlood specifies a flood filter primitive Standard reference: http://www.w3.org/TR/SVG11/filters.html#feFloodElement

FeFuncLinear(channel string, slope, intercept float64)

FeFuncLinear is the linear form of feFunc Standard reference: http://www.w3.org/TR/SVG11/filters.html#feComponentTransferElement

 FeFuncGamma(channel, amplitude, exponent, offset float64)

FeFuncGamma is the gamma curve form of feFunc Standard reference: http://www.w3.org/TR/SVG11/filters.html#feComponentTransferElement

FeFuncTable(channel string, tv []float64)

FeFuncGamma is the form of feFunc using a table of values Standard reference: http://www.w3.org/TR/SVG11/filters.html#feComponentTransferElement

FeFuncDiscrete(channel string, tv []float64)

FeFuncGamma is the form of feFunc using discrete values Standard reference: http://www.w3.org/TR/SVG11/filters.html#feComponentTransferElement

 FeGaussianBlur(fs Filterspec, stdx, stdy float64, s ...string)

FeGaussianBlur specifies a Gaussian Blur filter primitive Standard reference: http://www.w3.org/TR/SVG11/filters.html#feGaussianBlurElement

 FeImage(href string, result string, s ...string)

FeImage specifies a feImage filter primitive Standard reference: http://www.w3.org/TR/SVG11/filters.html#feImageElement

 FeMerge(nodes []string, s ...string)

FeMerge specifies a feMerge filter primitive, containing feMerge Element>s Standard reference: http://www.w3.org/TR/SVG11/filters.html#feMergeElement

 FeMorphology(fs Filterspec, operator string, xradius, yradius float64, s ...string)

FeMorphologyLight specifies a feMorphologyLight filter primitive Standard reference: http://www.w3.org/TR/SVG11/filters.html#feMorphologyElement

 FeOffset(fs Filterspec, dx, dy int, s ...string)

FeOffset specifies the feOffset filter primitive Standard reference: http://www.w3.org/TR/SVG11/filters.html#feOffsetElement

 FePointLight(x, y, z float64, s ...string)

FePointLight specifies a fePpointLight filter primitive Standard reference: http://www.w3.org/TR/SVG11/filters.html#fePointLightElement

 FeSpecularLighting(fs Filterspec, scale, constant float64, exponent int, color string, s ...string)

FeSpecularLighting specifies a specular lighting filter primitive, a container for light source elements, end with SpecularEnd()

 FeSpecEnd()

FeSpecularEnd ends a specular lighting filter primitive container Standard reference: http://www.w3.org/TR/SVG11/filters.html#feSpecularLightingElement

 FeSpotLight(fs Filterspec, x, y, z, px, py, pz float64, s ...string)

FeSpotLight specifies a feSpotLight filter primitive Standard reference: http://www.w3.org/TR/SVG11/filters.html#feSpotLightElement

 FeTile(fs Filterspec, in string, s ...string)

FeTile specifies the tile utility filter primitive Standard reference: http://www.w3.org/TR/SVG11/filters.html#feTileElement

 FeTurbulence(fs Filterspec, ftype string, bfx, bfy float64, octaves int, seed int64, stitch bool, s ...string)

FeTurbulence specifies a turbulence filter primitive Standard reference: http://www.w3.org/TR/SVG11/filters.html#feTurbulenceElement

Filter convenience functions (modeled on CSS filter effects)

Blur(p float64)

Blur function by standard deviation

Brightness(p float64)

Brightness function (0-100)

Grayscale()

Apply a grayscale filter to the image

HueRotate(a float64)

Rotate Hues (0-360 degrees)

Invert()

Invert the image's colors

Saturate(p float64)

Percent saturation, 0 is grayscale

Sepia()

Apply sepia tone

Utility

Grid(x int, y int, w int, h int, n int, s ...string)

draws a grid of straight lines starting at x,y, with a width w, and height h, and a size of n.

Credits

Thanks to Jonathan Wright for the io.Writer update.