第2話：画像に仕込む魔法！LINEイメージマップとスタンプの格闘記

{
  "type": "imagemap",
  "baseUrl": "https://example.com/card",
  "altText": "スタンプカード",
  "baseSize": { "height": 1040, "width": 1040 },
  "actions": [
    {
      "type": "message",
      "text": "stamp_1",
      "area": { "x": 100, "y": 200, "width": 200, "height": 200 }
    }
  ]
}

def generate_imagemap_actions(request, course_id):
    scale = course.stamp_scale or 1.0
    positions = CourseStampPosition.objects.filter(course=course).select_related("spot")

    actions = []
    for pos in positions:
        spot = pos.spot
        actions.append({
            "type": "message",
            "text": spot.keyword,
            "area": {
                "x": int(pos.x + 6 * scale),
                "y": int(pos.y + 6 * scale),
                "width": int(28 * scale),
                "height": int(28 * scale),
            }
        })

    return JsonResponse(actions, safe=False)

# 指定されたスタンプIDと獲得状態でスタンプ画像を返す 未獲得の場合は灰色の画像を返す
def render_stamp_image(request, reply_token, stamp_id, acquired_id):

    image_path = os.path.join(settings.MEDIA_ROOT, stamp.image.name)
    image = Image.open(image_path).convert("RGBA")

    if int(acquired_id) == 0:
        # NumPyで処理
        gray = image.convert("L")
        gray_array = np.array(gray)
        alpha_mask = gray_array < 50  # しきい値以下のみ対象

        # 新しいRGBA画像（すべて透明）
        result_array = np.zeros((image.height, image.width, 4), dtype=np.uint8)
        result_array[alpha_mask] = [200, 200, 200, 255]  # 灰色で表示

        result_image = Image.fromarray(result_array, mode="RGBA")
    else:
        result_image = image

    buffer = BytesIO()
    result_image.save(buffer, format="PNG")
    buffer.seek(0)
    return FileResponse(buffer, content_type="image/png")

path("course/<int:course_id>/<int:user_id>/<int:size>", views.render_user_stamp_card, name="render_user_stamp_card"),

# 指定されたコースとユーザーのスタンプカードを生成
def render_user_stamp_card(request, course_id, user_id, size):

    course = get_object_or_404(StampCourse, id=course_id)
    user = get_object_or_404(User, id=user_id)

    scale = course.stamp_scale or 1.0

    # 獲得済みスタンプのID（ユーザーが獲得済み、かつこのコースに含まれる）
    acquired_spots = UserStamp.objects.filter(user=user).values_list("stamp_id", flat=True)
    valid_spot_ids = course.spots.filter(id__in=acquired_spots).values_list("id", flat=True)

    # 元画像を読み込み
    base_path = os.path.join(settings.MEDIA_ROOT, course.image.name)
    base_image = Image.open(base_path).convert("RGBA")
    orig_width, orig_height = base_image.size

    canvas = base_image.copy()

    # スタンプを合成
    positions = CourseStampPosition.objects.filter(course=course, spot_id__in=valid_spot_ids).select_related("spot")
    for pos in positions:
        stamp_path = os.path.join(settings.MEDIA_ROOT, pos.spot.image.name)
        stamp = Image.open(stamp_path).convert("RGBA")
        size_px = int(40 * scale)
        stamp = stamp.resize((size_px, size_px), Image.LANCZOS)
        canvas.paste(stamp, (pos.x, pos.y), stamp)

    # 指定サイズにリサイズ（横幅基準）
    if size != orig_width:
        ratio = size / orig_width
        new_height = int(orig_height * ratio)
        canvas = canvas.resize((size, new_height), Image.LANCZOS)

    # 出力
    buffer = BytesIO()
    canvas.save(buffer, format="PNG")
    buffer.seek(0)
    return FileResponse(buffer, content_type="image/png")

path("course/<str:reply_token>/<int:course_id>/<int:user_id>/<int:size>", views.render_user_stamp_card, name="render_user_stamp_card"),