Added a pseudorandom noise pattern

artist/noise.go

@@ -0,0 +1,22 @@
+package artist
+
+import "image/color"
+
+// Noisy is a pattern that randomly interpolates between two patterns in a
+// deterministic fashion.
+type Noisy struct {
+	Low  Pattern
+	High Pattern
+	Seed uint32
+}
+
+// AtWhen satisfies the pattern interface.
+func (pattern Noisy) AtWhen (x, y, width, height int) (c color.RGBA) {
+	special := uint32(x + y * 348905)
+	special += (pattern.Seed + 1) * 15485863
+	random := (special * special * special % 2038074743)
+	fac := float64(random) / 2038074743.0
+	return LerpRGBA (
+		pattern.Low.AtWhen(x, y, width, height),
+		pattern.High.AtWhen(x, y, width, height), fac)
+}