Go Graphics

gg is a library for rendering 2D graphics in pure Go.

Installation

go get github.com/fogleman/gg

Hello, Circle!

Look how easy!

package main

import "github.com/fogleman/gg"

func main() {
    dc := gg.NewContext(1000, 1000)
    dc.DrawCircle(500, 500, 400)
    dc.SetRGB(0, 0, 0)
    dc.SetLineWidth(10)
    dc.Stroke()
    dc.SavePNG("out.png")
}

Creating Contexts

There are a few ways of creating a context.

NewContext(width, height int) *Context
NewContextForImage(im image.Image) *Context
NewContextForRGBA(im *image.RGBA) *Context

Drawing Functions

Ever used a graphics library that didn't have functions for drawing rectangles or circles? What a pain!

DrawLine(x1, y1, x2, y2 float64)
DrawRectangle(x, y, w, h float64)
DrawCircle(x, y, r float64)
DrawArc(x, y, r, angle1, angle2 float64)
DrawEllipse(x, y, rx, ry float64)
DrawEllipticalArc(x, y, rx, ry, angle1, angle2 float64)
DrawImage(im image.Image, x, y int)
DrawString(x, y float64, s string)

MoveTo(x, y float64)
LineTo(x, y float64)
QuadraticTo(x1, y1, x2, y2 float64)
ClosePath()
ClearPath()

Clear()
Stroke()
Fill()
StrokePreserve()
FillPreserve()

Color Functions

Colors can be set in several different ways for your convenience.

SetRGB(r, g, b float64)
SetRGBA(r, g, b, a float64)
SetRGB255(r, g, b int)
SetRGBA255(r, g, b, a int)
SetColor(c color.Color)
SetHexColor(x string)

Transformation Functions

All the usual matrix transformations are available too.

Identity()
Translate(x, y float64)
Scale(x, y float64)
Rotate(angle float64)
RotateAbout(angle, x, y float64)
Shear(x, y float64)
TransformPoint(x, y float64) (tx, ty float64)
Push()
Pop()

Helper Functions

Sometimes you just don't want to write these yourself.

Radians(degrees float64) float64
Degrees(radians float64) float64
LoadPNG(path string) (image.Image, error)
SavePNG(path string, im image.Image) error

What's Missing?

If you need any of the features below, I recommend using cairo instead.

Clipping Regions
Gradients / Patterns
Cubic Beziers
Dashed Lines

How Do it Do?

gg is mostly a wrapper around github.com/golang/freetype/raster. The goal is to provide some more functionality and a simpler API that will suffice for most use cases.

Another Example

See the output of this example below.

package main

import "github.com/fogleman/gg"

func main() {
	const S = 1024
	dc := gg.NewContext(S, S)
	dc.SetRGBA(0, 0, 0, 0.1)
	for i := 0; i < 360; i += 15 {
		dc.Push()
		dc.RotateAbout(gg.Radians(float64(i)), S/2, S/2)
		dc.DrawEllipse(S/2, S/2, S*7/16, S/8)
		dc.Fill()
		dc.Pop()
	}
	dc.SavePNG("out.png")
}

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