Move color averaging to package common

Also implement correct hue averaging in polar space

common/color.go

@@ -1,5 +1,7 @@
 package common
 
+import "math"
+
 // Color is used to represent the color and color temperature of a light.
 // The color is represented as a 48-bit HSB (Hue, Saturation, Brightness) value.
 // The color temperature is represented in K (Kelvin) and is used to adjust the
@@ -11,3 +13,40 @@ type Color struct {
 	Brightness uint16 // range 0 to 65535
 	Kelvin     uint16 // range 2500° (warm) to 9000° (cool)
 }
+
+// AverageColor returns the average of the provided colors
+func AverageColor(colors ...Color) (color Color) {
+	var (
+		x, y               float64
+		hue, sat, bri, kel int
+	)
+
+	// Sum sind/cosd for hues
+	for _, c := range colors {
+		// Convert hue to degrees
+		h := float64(c.Hue) / float64(math.MaxUint16) * 360.0
+
+		x += math.Cos(h / 180.0 * math.Pi)
+		y += math.Sin(h / 180.0 * math.Pi)
+		sat += int(c.Saturation)
+		bri += int(c.Brightness)
+		kel += int(c.Kelvin)
+	}
+
+	// Average sind/cosd
+	x /= float64(len(colors))
+	y /= float64(len(colors))
+
+	// Take atan2 of averaged hue and convert to uint16 scale
+	hue = int((math.Atan2(y, x) * 180.0 / math.Pi) / 360.0 * float64(math.MaxUint16))
+	sat /= len(colors)
+	bri /= len(colors)
+	kel /= len(colors)
+
+	color.Hue = uint16(hue)
+	color.Saturation = uint16(sat)
+	color.Brightness = uint16(bri)
+	color.Kelvin = uint16(kel)
+
+	return color
+}

protocol/v2/device/group.go

@@ -202,19 +202,16 @@ func (g *Group) CachedColor() common.Color {
 	return c
 }
 
-func (g *Group) getColor(cached bool) (common.Color, error) {
-	var (
-		hueSum, satSum, brightSum, kelvSum uint64
-		color                              common.Color
-	)
-
+func (g *Group) getColor(cached bool) (color common.Color, err error) {
 	lights := g.Lights()
 
 	if len(lights) == 0 {
 		return color, nil
 	}
 
-	for _, light := range lights {
+	colors := make([]common.Color, len(lights))
+
+	for i, light := range lights {
 		var (
 			c   common.Color
 			err error
@@ -227,16 +224,10 @@ func (g *Group) getColor(cached bool) (common.Color, error) {
 				return color, err
 			}
 		}
-		hueSum += uint64(c.Hue)
-		satSum += uint64(c.Saturation)
-		brightSum += uint64(c.Brightness)
-		kelvSum += uint64(c.Kelvin)
+		colors[i] = c
 	}
 
-	color.Hue = uint16(hueSum / uint64(len(lights)))
-	color.Saturation = uint16(satSum / uint64(len(lights)))
-	color.Brightness = uint16(brightSum / uint64(len(lights)))
-	color.Kelvin = uint16(kelvSum / uint64(len(lights)))
+	color = common.AverageColor(colors...)
 
 	return color, nil
 }