fix: v0.5.1 —— 导出窗口适配屏幕、去掉实时预览字样、图标加底板

- 导出预览窗口按屏幕可用高度计算尺寸，底部的「保存 PDF…」不会再顶出屏幕
- 默认欢迎文档去掉「实时预览（下一版）」，换成已实现的导出 PDF
- logo 是黑字透明底，放深色任务栏里等于看不见；packaging/generate_icons.py
  给它垫白色圆角底板并输出 16–256 多尺寸 ico，窗口图标与 exe 图标统一使用
- 新增 packaging/generate_icons.py，便于换图后重新生成
- 文档与截图同步

packaging/generate_icons.py

@@ -0,0 +1,177 @@
+#!/usr/bin/env python3
+"""从 logo.png 生成各平台图标。
+
+logo.png 是黑色字标 + 透明背景：放在深色 Windows 任务栏里会“看不见”。
+所以先给它加一块白色圆角底板，再导出 ico / icns / png。
+
+用法：python3 packaging/generate_icons.py
+"""
+
+import os
+import struct
+import subprocess
+
+ROOT = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
+SOURCE = os.path.join(ROOT, "logo.png")
+OUT_DIR = os.path.join(ROOT, "packaging")
+
+MASTER = 256
+SUPERSAMPLE = 2
+PLATE_RADIUS = 52
+GLYPH_RATIO = 0.66
+PLATE_COLOR = (255, 255, 255)
+BORDER_COLOR = (222, 226, 230)
+
+SIZES = (16, 24, 32, 48, 64, 128, 256)
+
+
+def run(args, **kwargs):
+    return subprocess.run(args, check=True, capture_output=True, **kwargs)
+
+
+def load_rgba(path, size):
+    return run(["ffmpeg", "-v", "error", "-i", path, "-vf",
+                f"scale={size}:{size}:flags=lanczos", "-pix_fmt", "rgba",
+                "-f", "rawvideo", "-"]).stdout
+
+
+def save_png(path, rgba, size):
+    run(["ffmpeg", "-y", "-v", "error", "-f", "rawvideo", "-pix_fmt", "rgba",
+         "-s", f"{size}x{size}", "-i", "-", path], input=rgba)
+
+
+def rounded_mask(size, radius):
+    """圆角矩形覆盖率，左上角为 (0,0)。"""
+    mask = bytearray(size * size)
+    r = radius
+    for y in range(size):
+        for x in range(size):
+            dx = min(x, size - 1 - x)
+            dy = min(y, size - 1 - y)
+            if dx >= r or dy >= r:
+                mask[y * size + x] = 255
+                continue
+            ddx = r - dx
+            ddy = r - dy
+            dist = (ddx * ddx + ddy * ddy) ** 0.5
+            if dist <= r:
+                mask[y * size + x] = 255
+    return mask
+
+
+def compose_master():
+    size = MASTER * SUPERSAMPLE
+    radius = PLATE_RADIUS * SUPERSAMPLE
+    border = 3 * SUPERSAMPLE
+    glyph_size = int(size * GLYPH_RATIO)
+    offset = (size - glyph_size) // 2
+
+    plate = rounded_mask(size, radius)
+    glyph = load_rgba(SOURCE, glyph_size)
+
+    canvas = bytearray(size * size * 4)
+    for y in range(size):
+        for x in range(size):
+            idx = (y * size + x) * 4
+            if not plate[y * size + x]:
+                continue
+            dx = min(x, size - 1 - x)
+            dy = min(y, size - 1 - y)
+            color = BORDER_COLOR if (dx < border or dy < border) else PLATE_COLOR
+            canvas[idx:idx + 4] = bytes((color[0], color[1], color[2], 255))
+
+    for gy in range(glyph_size):
+        for gx in range(glyph_size):
+            src = (gy * glyph_size + gx) * 4
+            alpha = glyph[src + 3] / 255.0
+            if alpha <= 0.0:
+                continue
+            dst = ((gy + offset) * size + (gx + offset)) * 4
+            for channel in range(3):
+                canvas[dst + channel] = int(
+                    glyph[src + channel] * alpha + canvas[dst + channel] * (1.0 - alpha))
+
+    # 缩小回 256，顺便得到平滑的边缘
+    return run(["ffmpeg", "-y", "-v", "error", "-f", "rawvideo", "-pix_fmt", "rgba",
+                "-s", f"{size}x{size}", "-i", "-", "-vf",
+                f"scale={MASTER}:{MASTER}:flags=lanczos", "-frames:v", "1",
+                "-f", "rawvideo", "-"], input=bytes(canvas)).stdout
+
+
+def bmp_entry(rgba, size):
+    header = struct.pack("<IiiHHIIiiII", 40, size, size * 2, 1, 32, 0,
+                         size * size * 4, 0, 0, 0, 0)
+    rows = []
+    for y in range(size - 1, -1, -1):
+        row = bytearray()
+        for x in range(size):
+            i = (y * size + x) * 4
+            r, g, b, a = rgba[i:i + 4]
+            row += bytes((b, g, r, a))
+        rows.append(bytes(row))
+
+    mask_row_bytes = ((size + 31) // 32) * 4
+    mask = bytearray()
+    for y in range(size - 1, -1, -1):
+        bits = bytearray(mask_row_bytes)
+        for x in range(size):
+            if rgba[(y * size + x) * 4 + 3] < 128:
+                bits[x // 8] |= 0x80 >> (x % 8)
+        mask += bits
+    return header + b"".join(rows) + bytes(mask)
+
+
+def write_ico(path, images):
+    header = struct.pack("<HHH", 0, 1, len(images))
+    offset = 6 + 16 * len(images)
+    entries = b""
+    payload = b""
+    for size, data in images:
+        dim = 0 if size >= 256 else size
+        entries += struct.pack("<BBBBHHII", dim, dim, 0, 0, 1, 32, len(data), offset)
+        payload += data
+        offset += len(data)
+    with open(path, "wb") as handle:
+        handle.write(header + entries + payload)
+
+
+def chunk(kind, data):
+    return kind + struct.pack(">I", 8 + len(data)) + data
+
+
+def main():
+    os.makedirs(OUT_DIR, exist_ok=True)
+
+    master = compose_master()
+    master_png = os.path.join(OUT_DIR, "voiletmark.png")
+    save_png(master_png, master, MASTER)
+
+    pngs = {}
+    master_bytes = open(master_png, "rb").read()
+    for size in SIZES:
+        if size == MASTER:
+            pngs[size] = master_bytes
+            continue
+        temp = os.path.join(OUT_DIR, f"_tmp_{size}.png")
+        run(["ffmpeg", "-y", "-v", "error", "-i", master_png, "-vf",
+             f"scale={size}:{size}:flags=lanczos", "-frames:v", "1", temp])
+        pngs[size] = open(temp, "rb").read()
+        os.remove(temp)
+
+    images = []
+    for size in SIZES:
+        if size == MASTER:
+            images.append((size, pngs[size]))
+        else:
+            images.append((size, bmp_entry(load_rgba(master_png, size), size)))
+    write_ico(os.path.join(OUT_DIR, "voiletmark.ico"), images)
+
+    body = chunk(b"ic07", pngs[128]) + chunk(b"ic08", pngs[256])
+    with open(os.path.join(OUT_DIR, "voiletmark.icns"), "wb") as handle:
+        handle.write(b"icns" + struct.pack(">I", 8 + len(body)) + body)
+
+    print("icons written to", OUT_DIR)
+
+
+if __name__ == "__main__":
+    main()