add crisp lines example

examples/crisp.go

@@ -0,0 +1,44 @@
+package main
+
+import (
+	"github.com/fogleman/gg"
+)
+
+func main() {
+	const W = 1000
+	const H = 1000
+	const Minor = 10
+	const Major = 100
+
+	dc := gg.NewContext(W, H)
+	dc.SetRGB(1, 1, 1)
+	dc.Clear()
+
+	// minor grid
+	for x := Minor; x < W; x += Minor {
+		fx := float64(x) + 0.5
+		dc.DrawLine(fx, 0, fx, H)
+	}
+	for y := Minor; y < H; y += Minor {
+		fy := float64(y) + 0.5
+		dc.DrawLine(0, fy, W, fy)
+	}
+	dc.SetLineWidth(1)
+	dc.SetRGBA(0, 0, 0, 0.25)
+	dc.Stroke()
+
+	// major grid
+	for x := Major; x < W; x += Major {
+		fx := float64(x) + 0.5
+		dc.DrawLine(fx, 0, fx, H)
+	}
+	for y := Major; y < H; y += Major {
+		fy := float64(y) + 0.5
+		dc.DrawLine(0, fy, W, fy)
+	}
+	dc.SetLineWidth(1)
+	dc.SetRGBA(0, 0, 0, 0.5)
+	dc.Stroke()
+
+	dc.SavePNG("out.png")
+}