ws2812: wrap Device in Strip instead of custom writeFunc

Refactor Strip to compose the existing Device type, using its
writeColorFunc to inject PIO behavior on RP2040/RP2350 instead of
a separate write closure. Also fix brightness math off-by-one
(255*255>>8 = 254) and pre-allocate the adjusted pixel buffer to
avoid allocation on every Show() call.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: gandarez

ws2812/strip.go

@@ -5,12 +5,14 @@ import "image/color"
 // Strip controls a strip of WS2812B LEDs with a pixel buffer and brightness control.
 // Use NewStrip to create a new instance.
 type Strip struct {
+	dev        Device
 	pixels     []color.RGBA
+	adjusted   []color.RGBA
 	brightness uint8
-	writeFunc  func(pixels []color.RGBA, brightness uint8) error
 }
 
 // SetPixel sets the color of pixel at index i.
+// Out-of-range indices are silently ignored.
 func (s *Strip) SetPixel(i int, c color.RGBA) {
 	if i >= 0 && i < len(s.pixels) {
 		s.pixels[i] = c
@@ -19,7 +21,10 @@ func (s *Strip) SetPixel(i int, c color.RGBA) {
 
 // Show sends the current pixel buffer to the LED strip.
 func (s *Strip) Show() error {
-	return s.writeFunc(s.pixels, s.brightness)
+	for i, c := range s.pixels {
+		s.adjusted[i] = applyBrightness(c, s.brightness)
+	}
+	return s.dev.WriteColors(s.adjusted)
 }
 
 // SetBrightness sets the global brightness (0-255).
@@ -45,9 +50,14 @@ func (s *Strip) NumPixels() int {
 }
 
 // applyBrightness scales a color by the brightness value.
-func applyBrightness(c color.RGBA, brightness uint8) (r, g, b uint8) {
-	r = uint8((uint16(c.R) * uint16(brightness)) >> 8)
-	g = uint8((uint16(c.G) * uint16(brightness)) >> 8)
-	b = uint8((uint16(c.B) * uint16(brightness)) >> 8)
-	return
+func applyBrightness(c color.RGBA, brightness uint8) color.RGBA {
+	if brightness == 255 {
+		return c
+	}
+	return color.RGBA{
+		R: uint8((uint16(c.R) * (uint16(brightness) + 1)) >> 8),
+		G: uint8((uint16(c.G) * (uint16(brightness) + 1)) >> 8),
+		B: uint8((uint16(c.B) * (uint16(brightness) + 1)) >> 8),
+		A: c.A,
+	}
 }

ws2812/strip_other.go

@@ -11,17 +11,10 @@ import (
 // number of pixels. On platforms without PIO, it uses the bit-bang driver.
 func NewStrip(pin machine.Pin, numPixels int) (*Strip, error) {
 	pin.Configure(machine.PinConfig{Mode: machine.PinOutput})
-	dev := NewWS2812(pin)
 	return &Strip{
+		dev:        NewWS2812(pin),
 		pixels:     make([]color.RGBA, numPixels),
+		adjusted:   make([]color.RGBA, numPixels),
 		brightness: 255,
-		writeFunc: func(pixels []color.RGBA, brightness uint8) error {
-			adjusted := make([]color.RGBA, len(pixels))
-			for i, c := range pixels {
-				r, g, bl := applyBrightness(c, brightness)
-				adjusted[i] = color.RGBA{R: r, G: g, B: bl}
-			}
-			return dev.WriteColors(adjusted)
-		},
 	}, nil
 }

ws2812/strip_rp2.go

@@ -21,15 +21,19 @@ func NewStrip(pin machine.Pin, numPixels int) (*Strip, error) {
 	if err != nil {
 		return nil, err
 	}
-	return &Strip{
-		pixels:     make([]color.RGBA, numPixels),
-		brightness: 255,
-		writeFunc: func(pixels []color.RGBA, brightness uint8) error {
-			for _, c := range pixels {
-				r, g, bl := applyBrightness(c, brightness)
-				ws.PutRGB(r, g, bl)
+	dev := Device{
+		Pin: pin,
+		writeColorFunc: func(d Device, buf []color.RGBA) error {
+			for _, c := range buf {
+				ws.PutRGB(c.R, c.G, c.B)
 			}
 			return nil
 		},
+	}
+	return &Strip{
+		dev:        dev,
+		pixels:     make([]color.RGBA, numPixels),
+		adjusted:   make([]color.RGBA, numPixels),
+		brightness: 255,
 	}, nil
 }