From 61cfb8800ddfd16ff92ae56031d0725e0fec5b07 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E7=8E=8B=E5=BE=B7=E5=AE=87?= <kvtodev@outlook.com>
Date: Thu, 24 Sep 2026 17:24:28 +0800
Subject: [PATCH] =?UTF-8?q?=E6=9F=A5=E7=9C=8B=E5=99=A8=E8=AE=A4=E5=BE=97?=
 =?UTF-8?q?=20ASCII=20FBX=20=E7=9A=84=E5=AD=97=E8=8A=82=E5=BC=80=E5=A4=B4?=
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- packages/model3d-viewer/src/loader.ts：字节魔数多认一种 ASCII FBX 开头（`; FBX`，Blender 等工具的默认导出），此前这批文件在没显式给 format 时会被判 unsupported-format，尽管 FBXLoader 能解析
- packages/model3d-viewer/src/loader.ts：BOM / 前导空白的跳过抽成 resolveModel3dViewerContentStart，JSON 与 ASCII FBX 两处判据共用
- packages/model3d-viewer/src/loader.test.ts：补 ASCII FBX（含前导空白）的字节判定用例
---
 packages/model3d-viewer/src/loader.test.ts | 13 +++++++++
 packages/model3d-viewer/src/loader.ts      | 33 ++++++++++++++++++----
 2 files changed, 41 insertions(+), 5 deletions(-)

diff --git a/packages/model3d-viewer/src/loader.test.ts b/packages/model3d-viewer/src/loader.test.ts
index a5d6cb88a..50413d648 100644
--- a/packages/model3d-viewer/src/loader.test.ts
+++ b/packages/model3d-viewer/src/loader.test.ts
@@ -84,6 +84,19 @@ describe('模型格式判定', () => {
         new TextEncoder().encode('\uFEFF{"asset":{}}'),
       ),
     ).toBe('gltf');
+    // ASCII FBX（Blender 默认导出）没有 Kaydara 魔数，按开头这行认。
+    expect(
+      resolveModel3dViewerFormatFromBytes(
+        new TextEncoder().encode(
+          '; FBX 7.4.0 project file\nFBXHeaderExtension: {',
+        ),
+      ),
+    ).toBe('fbx');
+    expect(
+      resolveModel3dViewerFormatFromBytes(
+        new TextEncoder().encode('\n  ; FBX 7.3.0 project file'),
+      ),
+    ).toBe('fbx');
     expect(
       resolveModel3dViewerFormatFromBytes(new Uint8Array([0x00, 0x01])),
     ).toBeNull();
diff --git a/packages/model3d-viewer/src/loader.ts b/packages/model3d-viewer/src/loader.ts
index 46707477a..f28303b8d 100644
--- a/packages/model3d-viewer/src/loader.ts
+++ b/packages/model3d-viewer/src/loader.ts
@@ -43,6 +43,8 @@ const MODEL3D_VIEWER_FBX_MAGIC = [
   0x4b, 0x61, 0x79, 0x64, 0x61, 0x72, 0x61, 0x20, 0x46, 0x42, 0x58, 0x20, 0x42,
   0x69, 0x6e, 0x61, 0x72, 0x79,
 ];
+/** ASCII FBX 的开头：「; FBX 7.4.0 project file」（Blender 等工具的默认导出）。 */
+const MODEL3D_VIEWER_ASCII_FBX_MAGIC = [0x3b, 0x20, 0x46, 0x42, 0x58];
 const MODEL3D_VIEWER_SUPPORTED_FORMAT_TEXT =
   MODEL3D_VIEWER_SUPPORTED_FORMATS.join(' / ');
 
@@ -56,18 +58,36 @@ function matchesModel3dViewerMagic(
   return magic.every((value, index) => bytes[index] === value);
 }
 
-function isModel3dViewerJsonStart(bytes: Uint8Array) {
-  for (const byte of bytes) {
-    // BOM 与空白之后是 `{` 才当 glTF JSON：多文件 glTF 的正文就是一个 JSON 文档。
+/** 跳过 BOM 与前导空白后的正文起点；全是噪声时返回 -1。 */
+function resolveModel3dViewerContentStart(bytes: Uint8Array) {
+  for (let index = 0; index < bytes.length; index += 1) {
+    const byte = bytes[index];
     if (byte === 0xef || byte === 0xbb || byte === 0xbf) {
       continue;
     }
     if (byte === 0x20 || byte === 0x09 || byte === 0x0a || byte === 0x0d) {
       continue;
     }
-    return byte === 0x7b;
+    return index;
   }
-  return false;
+  return -1;
+}
+
+function isModel3dViewerJsonStart(bytes: Uint8Array) {
+  // BOM 与空白之后是 `{` 才当 glTF JSON：多文件 glTF 的正文就是一个 JSON 文档。
+  const start = resolveModel3dViewerContentStart(bytes);
+  return start >= 0 && bytes[start] === 0x7b;
+}
+
+/** ASCII FBX 只有「看起来像」的判据，识别不出就交给显式 format 或扩展名。 */
+function isModel3dViewerAsciiFbxStart(bytes: Uint8Array) {
+  const start = resolveModel3dViewerContentStart(bytes);
+  if (start < 0) {
+    return false;
+  }
+  return MODEL3D_VIEWER_ASCII_FBX_MAGIC.every(
+    (value, offset) => bytes[start + offset] === value,
+  );
 }
 
 /** 声明类型里的模型格式；不是可渲染格式时返回 null。 */
@@ -96,6 +116,9 @@ export function resolveModel3dViewerFormatFromBytes(
   if (matchesModel3dViewerMagic(view, MODEL3D_VIEWER_FBX_MAGIC)) {
     return 'fbx';
   }
+  if (isModel3dViewerAsciiFbxStart(view)) {
+    return 'fbx';
+  }
   if (isModel3dViewerJsonStart(view)) {
     return 'gltf';
   }