Class FBXLoader

packages/asset-system/src/loaders/FBXLoader.ts:145–2193

 * FBX 模型加载器
 */
export class FBXLoader implements IAssetLoader<IGLTFAsset> {
    readonly supportedType = AssetType.Model3D;
    readonly supportedExtensions = ['.fbx'];
    readonly contentType: AssetContentType = 'binary';

    // Parsing state
    private buffer: ArrayBuffer = new ArrayBuffer(0);
    private view: DataView = new DataView(this.buffer);
    private offset = 0;
    private version = 0;

    /**
     * Parse FBX content
     * 解析 FBX 内容
     */
    async parse(content: IAssetContent, context: IAssetParseContext): Promise<IGLTFAsset> {
        const buffer = content.binary;
        if (!buffer) {
            throw new Error('FBX loader requires binary content');
        }

        // Detect format (binary or ASCII)
        // 检测格式（二进制或 ASCII）
        // FBX binary header is "Kaydara FBX Binary  \0" (21 bytes + null)
        // FBX 二进制头是 "Kaydara FBX Binary  \0"（21字节 + 空字节）
        const headerBytes = new Uint8Array(buffer, 0, Math.min(21, buffer.byteLength));
        const headerString = String.fromCharCode(...headerBytes);
        const isBinary = headerString.startsWith('Kaydara FBX Binary');

        let geometries: FBXGeometry[];
        let models: FBXModel[];
        let materials: FBXMaterial[];
        let animStacks: FBXAnimationStack[] = [];
        let deformers: FBXDeformer[] = [];
        let connections: FBXConnection[] = [];

        if (isBinary) {
            const result = this.parseBinary(buffer);
            geometries = result.geometries;
            models = result.models;
            materials = result.materials;
            animStacks = result.animStacks;
            deformers = result.deformers;
            connections = result.connections;
        } else {
            // Try ASCII parsing (no animation support for ASCII yet)
            // 尝试 ASCII 解析（ASCII 格式暂不支持动画）
            const text = new TextDecoder().decode(buffer);
            const result = this.parseASCII(text);
            geometries = result.geometries;
            models = result.models;
            materials = result.materials;
        }

        // Build skeleton data FIRST to get cluster -> joint index mapping
        // 先构建骨骼数据以获取簇->关节索引映射
        const clusterToJointIndex = new Map<bigint, number>();
        const skeleton = this.buildSkeletonData(deformers, models, connections, clusterToJointIndex) ?? undefined;