gg
is a library for rendering 2D graphics in pure Go.
go get github.com/fogleman/gg
https://godoc.org/github.com/fogleman/gg
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.Fill()
dc.SavePNG("out.png")
}
There are a few ways of creating a context.
NewContext(width, height int) *Context
NewContextForImage(im image.Image) *Context
NewContextForRGBA(im *image.RGBA) *Context
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)
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)
DrawImage(im image.Image, x, y int)
DrawImageAnchored(im image.Image, x, y int, ax, ay float64)
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.
DrawString(s string, x, y float64)
DrawStringAnchored(s string, x, y, ax, ay float64)
MeasureString(s string) (w, h float64)
SetFontFace(fontFace font.Face)
LoadFontFace(path string, points float64)
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)
SetLineWidth(lineWidth float64)
SetLineCap(lineCap LineCap)
SetLineJoin(lineJoin LineJoin)
SetDash(dashes ...float64)
SetFillRule(fillRule FillRule)
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.
Note: transforms do not currently affect DrawImage
or DrawString
.
Save and restore the state of the context. These can be nested.
Push()
Pop()
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
If you need any of the features below, I recommend using cairo
instead. Or
even better, implement it and submit a pull request!
- Clipping Regions
- Gradients / Patterns
gg
is mostly a wrapper around github.com/golang/freetype/raster
. The goal
is to provide some more functionality and a nicer API that will suffice for
most use cases.
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")
}