Feature 06: PWA shell and offline (#58)

Co-authored-by: dev_agent <dev_agent@cubecraftlabs.com>

web/scripts/generate-icons/main.go

@@ -0,0 +1,186 @@
+// Command generate-icons writes the PWA icons in web/public from the
+// MealQuest logo. Run it from the repository root:
+//
+//	go run ./web/scripts/generate-icons
+//
+// The logo fills the regular icons edge to edge. The maskable icon shrinks it
+// onto the colour of its own parchment, so the banner stays inside the
+// circular safe zone (radius 40% of the icon) that launchers may crop to.
+package main
+
+import (
+	"fmt"
+	"image"
+	"image/color"
+	"image/png"
+	"math"
+	"os"
+	"path/filepath"
+	"slices"
+
+	"golang.org/x/image/draw"
+)
+
+const (
+	source        = "design/logos/logo_v1_2Oct2026.jpg"
+	public        = "web/public"
+	maskableScale = 0.66
+)
+
+func main() {
+	if err := run(); err != nil {
+		fmt.Fprintln(os.Stderr, "generate-icons:", err)
+		os.Exit(1)
+	}
+}
+
+func run() error {
+	logo, err := load(source)
+	if err != nil {
+		return err
+	}
+	if b := logo.Bounds(); b.Dx() != b.Dy() {
+		return fmt.Errorf("%s is %dx%d; the logo must be square", source, b.Dx(), b.Dy())
+	}
+	outputs := []struct {
+		path  string
+		image *image.RGBA
+	}{
+		{"icons/icon-192.png", resized(logo, 192)},
+		{"icons/icon-512.png", resized(logo, 512)},
+		{"icons/icon-maskable-512.png", maskable(logo, 512)},
+		{"apple-touch-icon.png", resized(logo, 180)},
+	}
+	for _, out := range outputs {
+		path := filepath.Join(public, out.path)
+		if err := save(path, out.image); err != nil {
+			return err
+		}
+		fmt.Printf("wrote %s (%dx%d)\n", path, out.image.Rect.Dx(), out.image.Rect.Dy())
+	}
+	return nil
+}
+
+// load decodes the logo. The file is a PNG despite its .jpg name, so the
+// format is sniffed rather than taken from the extension.
+func load(path string) (image.Image, error) {
+	f, err := os.Open(path)
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+	img, _, err := image.Decode(f)
+	if err != nil {
+		return nil, fmt.Errorf("decode %s: %w", path, err)
+	}
+	return img, nil
+}
+
+func save(path string, img image.Image) error {
+	if err := os.MkdirAll(filepath.Dir(path), 0o755); err != nil {
+		return err
+	}
+	f, err := os.Create(path)
+	if err != nil {
+		return err
+	}
+	enc := png.Encoder{CompressionLevel: png.BestCompression}
+	if err := enc.Encode(f, img); err != nil {
+		f.Close()
+		return fmt.Errorf("encode %s: %w", path, err)
+	}
+	return f.Close()
+}
+
+func resized(logo image.Image, size int) *image.RGBA {
+	dst := image.NewRGBA(image.Rect(0, 0, size, size))
+	draw.CatmullRom.Scale(dst, dst.Rect, logo, logo.Bounds(), draw.Src, nil)
+	return dst
+}
+
+func maskable(logo image.Image, size int) *image.RGBA {
+	// The padding is the median colour of the logo's top edge, which is bare
+	// parchment; a feathered edge hides the seam.
+	b := logo.Bounds()
+	canvas := image.NewRGBA(image.Rect(0, 0, size, size))
+	draw.Draw(canvas, canvas.Rect, image.NewUniform(medianColour(logo, image.Rect(b.Min.X, b.Min.Y, b.Max.X, b.Min.Y+b.Dy()/40))), image.Point{}, draw.Src)
+	inner := int(math.Round(float64(size) * maskableScale))
+	offset := (size - inner) / 2
+	margin := inner / 24
+	at := image.Rect(offset, offset, offset+inner, offset+inner)
+	draw.DrawMask(canvas, at, resized(logo, inner), image.Point{}, feather(inner, margin), image.Point{}, draw.Over)
+	return canvas
+}
+
+// medianColour is the per-channel median of the pixels in r.
+func medianColour(img image.Image, r image.Rectangle) color.RGBA {
+	var channels [3][]uint8
+	for y := r.Min.Y; y < r.Max.Y; y++ {
+		for x := r.Min.X; x < r.Max.X; x++ {
+			c := color.RGBAModel.Convert(img.At(x, y)).(color.RGBA)
+			channels[0] = append(channels[0], c.R)
+			channels[1] = append(channels[1], c.G)
+			channels[2] = append(channels[2], c.B)
+		}
+	}
+	var median [3]uint8
+	for i, values := range channels {
+		slices.Sort(values)
+		median[i] = values[len(values)/2]
+	}
+	return color.RGBA{R: median[0], G: median[1], B: median[2], A: 0xff}
+}
+
+// feather is an opaque square inset by margin on a size×size mask, its edge
+// softened by a Gaussian blur with a standard deviation of margin/2.
+func feather(size, margin int) *image.Alpha {
+	values := make([]float64, size*size)
+	for y := margin; y <= size-margin && y < size; y++ {
+		for x := margin; x <= size-margin && x < size; x++ {
+			values[y*size+x] = 255
+		}
+	}
+	kernel := gaussian(float64(margin) / 2)
+	values = blur(values, size, kernel, 1, size)
+	values = blur(values, size, kernel, size, 1)
+	mask := image.NewAlpha(image.Rect(0, 0, size, size))
+	for i, v := range values {
+		mask.Pix[i] = uint8(math.Round(min(max(v, 0), 255)))
+	}
+	return mask
+}
+
+// gaussian is a normalised kernel reaching three standard deviations.
+func gaussian(sigma float64) []float64 {
+	radius := int(math.Ceil(3 * sigma))
+	kernel := make([]float64, 2*radius+1)
+	var sum float64
+	for i := range kernel {
+		d := float64(i - radius)
+		kernel[i] = math.Exp(-d * d / (2 * sigma * sigma))
+		sum += kernel[i]
+	}
+	for i := range kernel {
+		kernel[i] /= sum
+	}
+	return kernel
+}
+
+// blur convolves each line of a size×size grid with kernel: step is the
+// distance between neighbours along a line and stride between lines. Samples
+// beyond the edge repeat the edge.
+func blur(values []float64, size int, kernel []float64, step, stride int) []float64 {
+	radius := len(kernel) / 2
+	out := make([]float64, len(values))
+	for line := range size {
+		for i := range size {
+			var v float64
+			for k, w := range kernel {
+				j := min(max(i+k-radius, 0), size-1)
+				v += w * values[line*stride+j*step]
+			}
+			out[line*stride+i*step] = v
+		}
+	}
+	return out
+}