Go Graphics (gg) 类似于draw2d golang图像处理库


func Rect(x1, y1, x2, y2, thickness int, img *image.RGBA) { 
    col := color.RGBA{0, 0, 0, 255} 

    for t:=0; t<thickness; t++ { 
     // draw horizontal lines 
     for x := x1; x<= x2; x++ { 
      img.Set(x, y1+t, col) 
      img.Set(x, y2-t, col) 
     // draw vertical lines 
     for y := y1; y <= y2; y++ { 
      img.Set(x1+t, y, col) 
      img.Set(x2-t, y, col) 

// handler to test 
func draw(w http.ResponseWriter, r *http.Request) { 
    img := image.NewRGBA(image.Rect(0, 0, 1200, 1800)) 
    Rect(5, 5, 1195, 1795, 2, img) 
    png.Encode(w, img) 

// HLine draws a horizontal line 
func HLine(x1, y, x2 int) { 
    for ; x1 <= x2; x1++ { 
     img.Set(x1, y, col) 

// VLine draws a veritcal line 
func VLine(x, y1, y2 int) { 
    for ; y1 <= y2; y1++ { 
     img.Set(x, y1, col) 

// Rect draws a rectangle utilizing HLine() and VLine() 
func Rect(x1, y1, x2, y2 int) { 
    HLine(x1, y1, x2) 
    HLine(x1, y2, x2) 
    VLine(x1, y1, y2) 
    VLine(x2, y1, y2) 

Go Graphics

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


go get -u 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)


There are included. They’re mostly for testing the code, but they’re good for learning, too.

Go Graphics (gg) 类似于draw2d golang图像处理库

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!

DrawPoint(x, y, r float64)
DrawLine(x1, y1, x2, y2 float64)
DrawRectangle(x, y, w, h float64)
DrawRoundedRectangle(x, y, w, h, r 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)
DrawRegularPolygon(n int, x, y, r, rotation float64)
DrawImage(im image.Image, x, y int)
DrawImageAnchored(im image.Image, x, y int, ax, ay float64)
SetPixel(x, y int)

MoveTo(x, y float64)
LineTo(x, y float64)
QuadraticTo(x1, y1, x2, y2 float64)
CubicTo(x1, y1, x2, y2, x3, y3 float64)


It is often desired to center an image at a point. Use DrawImageAnchored with ax and ay set to 0.5 to do this. Use 0 to left or top align. Use 1 to right or bottom align. DrawStringAnchored does the same for text, so you don’t need to call MeasureString yourself.

Text Functions

It will even do word wrap for you!

DrawString(s string, x, y float64)
DrawStringAnchored(s string, x, y, ax, ay float64)
DrawStringWrapped(s string, x, y, ax, ay, width, lineSpacing float64, align Align)
MeasureString(s string) (w, h float64)
MeasureMultilineString(s string, lineSpacing float64) (w, h float64)
WordWrap(s string, w float64) []string
SetFontFace(fontFace font.Face)
LoadFontFace(path string, points float64) error

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)

Stroke & Fill Options

SetLineWidth(lineWidth float64)
SetLineCap(lineCap LineCap)
SetLineJoin(lineJoin LineJoin)
SetDash(dashes ...float64)
SetDashOffset(offset float64)
SetFillRule(fillRule FillRule)

Gradients & Patterns

gg supports linear and radial gradients and surface patterns. You can also implement your own patterns.

SetFillStyle(pattern Pattern)
SetStrokeStyle(pattern Pattern)
NewSolidPattern(color color.Color)
NewLinearGradient(x0, y0, x1, y1 float64)
NewRadialGradient(x0, y0, r0, x1, y1, r1 float64)
NewSurfacePattern(im image.Image, op RepeatOp)

Transformation Functions

Translate(x, y float64)
Scale(x, y float64)
Rotate(angle float64)
Shear(x, y float64)
ScaleAbout(sx, sy, x, y float64)
RotateAbout(angle, x, y float64)
ShearAbout(sx, sy, x, y float64)
TransformPoint(x, y float64) (tx, ty float64)

It is often desired to rotate or scale about a point that is not the origin. The functions RotateAbout, ScaleAbout, ShearAbout are provided as a convenience.

InvertY is provided in case Y should increase from bottom to top vs. the default top to bottom.

Stack Functions

Save and restore the state of the context. These can be nested.


Clipping Functions

Use clipping regions to restrict drawing operations to an area that you
defined using paths.

AsMask() *image.Alpha
SetMask(mask *image.Alpha)

Helper Functions

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

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

Go Graphics (gg) 类似于draw2d golang图像处理库

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.RotateAbout(gg.Radians(float64(i)), S/2, S/2)
		dc.DrawEllipse(S/2, S/2, S*7/16, S/8)

Go Graphics (gg) 类似于draw2d golang图像处理库

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2020-5-14 13:31:11


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