Go Graphics

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

Installation

go get -u github.com/FloatTech/gg

Alternatively, you may use gopkg.in to grab a specific major-version:

go get -u github.com/FloatTech/gg.v1

Documentation

• godoc: https://godoc.org/github.com/FloatTech/gg
• pkg.go.dev: https://pkg.go.dev/github.com/FloatTech/gg?tab=doc

Hello, Circle!

Look how easy!

package main
import"github.com/FloatTech/gg"funcmain() {
dc:=gg.NewContext(1000, 1000)
dc.DrawCircle(500, 500, 400)
dc.SetRGB(0, 0, 0)
dc.Fill()
dc.SavePNG("out.png")
}

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, heightint) *ContextNewContextForImage(imimage.Image) *ContextNewContextForRGBA(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, rfloat64)
DrawLine(x1, y1, x2, y2float64)
DrawRectangle(x, y, w, hfloat64)
DrawRoundedRectangle(x, y, w, h, rfloat64)
DrawCircle(x, y, rfloat64)
DrawArc(x, y, r, angle1, angle2float64)
DrawEllipse(x, y, rx, ryfloat64)
DrawEllipticalArc(x, y, rx, ry, angle1, angle2float64)
DrawRegularPolygon(nint, x, y, r, rotationfloat64)
DrawImage(imimage.Image, x, yint)
DrawImageAnchored(imimage.Image, x, yint, ax, ayfloat64)
SetPixel(x, yint)
MoveTo(x, yfloat64)
LineTo(x, yfloat64)
QuadraticTo(x1, y1, x2, y2float64)
CubicTo(x1, y1, x2, y2, x3, y3float64)
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(sstring, x, yfloat64)
DrawStringAnchored(sstring, x, y, ax, ayfloat64)
DrawStringWrapped(sstring, x, y, ax, ay, width, lineSpacingfloat64, alignAlign)
MeasureString(sstring) (w, hfloat64)
MeasureMultilineString(sstring, lineSpacingfloat64) (w, hfloat64)
WordWrap(sstring, wfloat64) []stringSetFontFace(fontFacefont.Face)
LoadFontFace(pathstring, pointsfloat64) error

Color Functions

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

SetRGB(r, g, bfloat64)
SetRGBA(r, g, b, afloat64)
SetRGB255(r, g, bint)
SetRGBA255(r, g, b, aint)
SetColor(ccolor.Color)
SetHexColor(xstring)

Stroke & Fill Options

SetLineWidth(lineWidthfloat64)
SetLineCap(lineCapLineCap)
SetLineJoin(lineJoinLineJoin)
SetDash(dashes...float64)
SetDashOffset(offsetfloat64)
SetFillRule(fillRuleFillRule)

Gradients & Patterns

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

SetFillStyle(patternPattern)
SetStrokeStyle(patternPattern)
NewSolidPattern(colorcolor.Color)
NewLinearGradient(x0, y0, x1, y1float64)
NewRadialGradient(x0, y0, r0, x1, y1, r1float64)
NewConicGradient(cx, cy, degfloat64)
NewSurfacePattern(imimage.Image, opRepeatOp)

Transformation Functions

Identity()
Translate(x, yfloat64)
Scale(x, yfloat64)
Rotate(anglefloat64)
Shear(x, yfloat64)
ScaleAbout(sx, sy, x, yfloat64)
RotateAbout(angle, x, yfloat64)
ShearAbout(sx, sy, x, yfloat64)
TransformPoint(x, yfloat64) (tx, tyfloat64)
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.AlphaSetMask(mask*image.Alpha)
InvertMask()

Helper Functions

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

Radians(degreesfloat64) float64Degrees(radiansfloat64) float64LoadImage(pathstring) (image.Image, error)
LoadPNG(pathstring) (image.Image, error)
SavePNG(pathstring, imimage.Image) error

Another Example

See the output of this example below.

package main
import"github.com/FloatTech/gg"funcmain() {
constS=1024dc:=gg.NewContext(S, S)
dc.SetRGBA(0, 0, 0, 0.1)
fori:=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")
}