feat(bskyweb): composite invite pass strip image

bskyweb/cmd/bskyweb/passimage.go

@@ -0,0 +1,99 @@
+package main
+
+import (
+	"bytes"
+	"image"
+	"image/color"
+	"image/png"
+	"io/fs"
+	"strconv"
+
+	"golang.org/x/image/draw"
+	"golang.org/x/image/font"
+	"golang.org/x/image/math/fixed"
+)
+
+// CompositeStrip overlays a circular avatar and centered handle text onto the
+// per-theme gradient base. Returns PNG bytes. If avatar is nil, a white circle
+// is drawn as the fallback (the Bluesky butterfly is rendered by the client
+// dialog only; the pass uses an empty circle to keep the server stateless w.r.t.
+// brand vector assets).
+func CompositeStrip(base image.Image, avatar image.Image, handle string, fontFace font.Face) ([]byte, error) {
+	bounds := base.Bounds()
+	dst := image.NewRGBA(bounds)
+	draw.Draw(dst, bounds, base, bounds.Min, draw.Src)
+
+	cx := bounds.Dx() / 2
+	cy := bounds.Dy() / 3
+	radius := bounds.Dy() / 4
+
+	mask := newCircleMask(image.Point{X: cx, Y: cy}, radius, bounds)
+	if avatar != nil {
+		fit := fitToSquare(avatar, radius*2)
+		draw.DrawMask(dst, image.Rect(cx-radius, cy-radius, cx+radius, cy+radius),
+			fit, image.Point{}, mask, image.Point{X: cx - radius, Y: cy - radius}, draw.Over)
+	} else {
+		white := &image.Uniform{C: image.White}
+		draw.DrawMask(dst, image.Rect(cx-radius, cy-radius, cx+radius, cy+radius),
+			white, image.Point{}, mask, image.Point{X: cx - radius, Y: cy - radius}, draw.Over)
+	}
+
+	label := "@" + handle
+	drawer := &font.Drawer{
+		Dst:  dst,
+		Src:  &image.Uniform{C: image.White},
+		Face: fontFace,
+	}
+	advance := drawer.MeasureString(label)
+	drawer.Dot = fixed.Point26_6{
+		X: fixed.I(cx) - advance/2,
+		Y: fixed.I(cy + radius + fontFace.Metrics().Ascent.Ceil() + 4),
+	}
+	drawer.DrawString(label)
+
+	var buf bytes.Buffer
+	if err := png.Encode(&buf, dst); err != nil {
+		return nil, err
+	}
+	return buf.Bytes(), nil
+}
+
+func LoadGradientBase(staticFS fs.FS, theme string, scale int) (image.Image, error) {
+	theme = CoerceTheme(theme)
+	name := "passes/strip-" + theme + densitySuffix(scale) + ".png"
+	f, err := staticFS.Open(name)
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+	img, _, err := image.Decode(f)
+	return img, err
+}
+
+func densitySuffix(scale int) string {
+	if scale <= 1 {
+		return ""
+	}
+	return "@" + strconv.Itoa(scale) + "x"
+}
+
+func newCircleMask(center image.Point, radius int, area image.Rectangle) *image.Alpha {
+	mask := image.NewAlpha(area)
+	r2 := radius * radius
+	for y := area.Min.Y; y < area.Max.Y; y++ {
+		dy := y - center.Y
+		for x := area.Min.X; x < area.Max.X; x++ {
+			dx := x - center.X
+			if dx*dx+dy*dy <= r2 {
+				mask.SetAlpha(x, y, color.Alpha{255})
+			}
+		}
+	}
+	return mask
+}
+
+func fitToSquare(src image.Image, size int) image.Image {
+	dst := image.NewRGBA(image.Rect(0, 0, size, size))
+	draw.CatmullRom.Scale(dst, dst.Bounds(), src, src.Bounds(), draw.Over, nil)
+	return dst
+}

bskyweb/cmd/bskyweb/passimage_test.go

@@ -0,0 +1,49 @@
+package main
+
+import (
+	"bytes"
+	"image"
+	_ "image/png"
+	"os"
+	"testing"
+
+	"golang.org/x/image/font/basicfont"
+)
+
+func TestCompositeStrip_ProducesValidPNG(t *testing.T) {
+	baseF, _ := os.Open("testdata/strip-day-base.png")
+	defer baseF.Close()
+	base, _, err := image.Decode(baseF)
+	if err != nil {
+		t.Fatalf("base decode: %v", err)
+	}
+	avF, _ := os.Open("testdata/avatar-test.png")
+	defer avF.Close()
+	avatar, _, err := image.Decode(avF)
+	if err != nil {
+		t.Fatalf("avatar decode: %v", err)
+	}
+	got, err := CompositeStrip(base, avatar, "alice.bsky.social", basicfont.Face7x13)
+	if err != nil {
+		t.Fatalf("composite: %v", err)
+	}
+	if len(got) < 100 {
+		t.Fatalf("output too small to be valid PNG: %d bytes", len(got))
+	}
+	if _, _, err := image.Decode(bytes.NewReader(got)); err != nil {
+		t.Fatalf("output not a valid PNG: %v", err)
+	}
+}
+
+func TestCompositeStrip_NilAvatarFallsBack(t *testing.T) {
+	baseF, _ := os.Open("testdata/strip-day-base.png")
+	defer baseF.Close()
+	base, _, _ := image.Decode(baseF)
+	got, err := CompositeStrip(base, nil, "alice.bsky.social", basicfont.Face7x13)
+	if err != nil {
+		t.Fatalf("composite: %v", err)
+	}
+	if _, _, err := image.Decode(bytes.NewReader(got)); err != nil {
+		t.Fatalf("output not a valid PNG: %v", err)
+	}
+}