added an example for software rendering

updated readme

README.md

@@ -12,7 +12,9 @@ The OpenGL backend is intended to provide decent performance. Obviously it will
 
 ## Software backend
 
-The software backend can also be used if no OpenGL context is available. It will render into a standard Go RGBA image.
+The software backend can also be used if no OpenGL context is available. It will render into a standard Go RGBA image. 
+
+There is experimental MSAA anti-aliasing, but it doesn't fully work properly yet. The best option for anti-aliasing currently is to render to a larger image and then scale it down.
 
 ## SDL/GLFW convenience packages
 

examples/software/software.go

@@ -0,0 +1,43 @@
+package main
+
+import (
+	"image/png"
+	"math"
+	"os"
+
+	"github.com/tfriedel6/canvas"
+	"github.com/tfriedel6/canvas/backend/softwarebackend"
+)
+
+func main() {
+	backend := softwarebackend.New(720, 720)
+	cv := canvas.New(backend)
+
+	w, h := float64(cv.Width()), float64(cv.Height())
+	cv.SetFillStyle("#000")
+	cv.FillRect(0, 0, w, h)
+
+	for r := 0.0; r < math.Pi*2; r += math.Pi * 0.1 {
+		cv.SetFillStyle(int(r*10), int(r*20), int(r*40))
+		cv.BeginPath()
+		cv.MoveTo(w*0.5, h*0.5)
+		cv.Arc(w*0.5, h*0.5, math.Min(w, h)*0.4, r, r+0.1*math.Pi, false)
+		cv.ClosePath()
+		cv.Fill()
+	}
+
+	cv.SetStrokeStyle("#FFF")
+	cv.SetLineWidth(10)
+	cv.BeginPath()
+	cv.Arc(w*0.5, h*0.5, math.Min(w, h)*0.4, 0, math.Pi*2, false)
+	cv.Stroke()
+
+	f, err := os.OpenFile("result.png", os.O_CREATE|os.O_TRUNC|os.O_WRONLY, 0777)
+	if err != nil {
+		panic(err)
+	}
+	err = png.Encode(f, backend.Image)
+	if err != nil {
+		panic(err)
+	}
+}