Go Graphics
gg
is a library for rendering 2D graphics in pure Go.
git.sr.ht/~sbinet/gg
is a fork of fogleman/gg which doesn't seem to be maintained (as of January 2022).
Installation
go get -u git.sr.ht/~sbinet/gg
Documentation
Hello, Circle!
Look how easy!
func ExampleCircle() {
dc := gg.NewContext(1000, 1000)
dc.DrawCircle(500, 500, 400)
dc.SetRGB(0, 0, 0)
dc.Fill()
err := dc.SavePNG("testdata/circle.png")
if err != nil {
log.Fatalf("could not save to file: %+v", err)
}
}
Examples
There are lots of examples included. They're mostly for testing the code, but they're good for learning, too.
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)
ClosePath()
ClearPath()
NewSubPath()
Clear()
Stroke()
Fill()
StrokePreserve()
FillPreserve()
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
LoadFontFaceFromBytes(raw []byte, points float64) error
LoadFontFaceFromFS(fsys fs.FS, 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, radial and conic 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)
NewConicGradient(cx, cy, deg float64)
NewSurfacePattern(im image.Image, op RepeatOp)
Transformation Functions
Identity()
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)
InvertY()
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.
Push()
Pop()
Clipping Functions
Use clipping regions to restrict drawing operations to an area that you
defined using paths.
Clip()
ClipPreserve()
ResetClip()
AsMask() *image.Alpha
SetMask(mask *image.Alpha)
InvertMask()
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
Another Example
See the output of this example below.
func ExampleEllipse() {
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()
}
im, err := gg.LoadImage("testdata/gopher.png")
if err != nil {
panic(err)
}
dc.DrawImageAnchored(im, S/2, S/2, 0.5, 0.5)
err = dc.SavePNG("testdata/ellipse.png")
if err != nil {
log.Fatalf("could not save to file: %+v", err)
}
}