scripts/probes/fbx_embed_texture.py

#!/usr/bin/env python3
"""Graft an embedded texture into a binary FBX that references one externally.

    fbx_embed_texture.py --selftest <fbx>...          byte-identical round trip
    fbx_embed_texture.py --donor <fbx> <fbx>...       copy the donor's Video/Content
                                                      into each target, in place

Truebones embeds its textures in the FBX itself — 73 of the 74 species carry the
pixels in a `Video/Content` property, so a clip renders correctly wherever it is
opened. `Cat` is the exception: its four standalone clips were exported without
"embed media", so they carry only a `RelativeFilename` pointing at a `Cat.fbm/`
directory that does not exist. They render untextured from `animation/`, whose
flat layout puts no image anywhere the importer's search can reach.

The fix is not a re-export, which would rebuild the rig. The file is parsed into
its node tree, one `Content` node is inserted into `Video`, and the tree is
re-serialized with recomputed offsets — every node record stores an absolute end
offset, so an insertion shifts everything after it. Nothing else is touched.

The `Content` node is copied verbatim from a donor file of the same species that
does have it (`Cat-ALL.fbx`), rather than synthesised, so the property encoding
and node framing are known-good rather than guessed.

Correctness gate: with no edits the serializer must reproduce its input byte for
byte (`--selftest`). Some nodes carry a trailing null record despite having no
children; that is tracked per node so round trips stay exact.

Writes through a temporary file and renames it into place. Every clip here is a
hardlink of one in `Truebone_Z-OO/`, and writing to such a path writes through to
the original.
"""
import os, struct, sys

ELEM = {'f':4,'d':8,'l':8,'i':4,'b':1}
SCALAR = {"Y":2,"C":1,"I":4,"F":4,"D":8,"L":8}


class Node:
    __slots__ = ("name","props","children","nullrec")
    def __init__(s, name): s.name=name; s.props=[]; s.children=[]; s.nullrec=False


def parse(path):
    d=open(path,'rb').read()
    assert d[:21]==b"Kaydara FBX Binary  \x00", "not a binary FBX"
    version=struct.unpack("<I",d[23:27])[0]; u64=version>=7500
    NREC=25 if u64 else 13

    def rd_prop(p):
        t=chr(d[p]); s=p; p+=1
        if t in SCALAR:
            p+=SCALAR[t]; return p,(t,d[s+1:p])
        if t in ELEM:
            length,enc,clen=struct.unpack("<III",d[p:p+12]); hdr=d[p:p+12]; p+=12
            body=clen if enc else length*ELEM[t]
            data=d[p:p+body]; p+=body
            return p,(t,hdr+data)
        if t in "SR":
            ln=struct.unpack("<I",d[p:p+4])[0]; p+=4
            data=d[p:p+ln]; p+=ln
            return p,(t,data)
        raise ValueError("bad prop type %r @%d"%(t,s))

    def is_null(p): return p+NREC<=len(d) and d[p:p+NREC]==b"\x00"*NREC

    def rd_node(p):
        if u64: end,nprop,plen=struct.unpack("<QQQ",d[p:p+24]); q=p+24
        else:   end,nprop,plen=struct.unpack("<III",d[p:p+12]); q=p+12
        if end==0 and nprop==0 and plen==0: return None,p+NREC
        nl=d[q]; q+=1; name=d[q:q+nl]; q+=nl
        n=Node(name); p=q
        for _ in range(nprop):
            p,pr=rd_prop(p); n.props.append(pr)
        while p<end:
            if is_null(p): n.nullrec=True; p+=NREC; break
            c,p2=rd_node(p)
            if c is None: n.nullrec=True; p=p2; break
            n.children.append(c); p=p2
        return n,end

    p=27; top=[]; tnull=False
    while p<len(d):
        if is_null(p): tnull=True; p+=NREC; break
        n,p2=rd_node(p)
        if n is None: tnull=True; p=p2; break
        top.append(n); p=p2
    return {"header":d[:27],"u64":u64,"top":top,"footer":d[p:],
            "toplevel_null":tnull,"orig":d,"version":version}


def pbytes(t,pay):
    if t in "SR": return t.encode()+struct.pack("<I",len(pay))+pay
    return t.encode()+pay

def nsize(n,u64):
    NREC=25 if u64 else 13
    sz=NREC+len(n.name)
    sz+=sum(len(pbytes(t,p)) for t,p in n.props)
    sz+=sum(nsize(c,u64) for c in n.children)
    if n.nullrec: sz+=NREC
    return sz

def wnode(out,n,u64):
    NREC=25 if u64 else 13
    props=b"".join(pbytes(t,p) for t,p in n.props)
    end=len(out)+nsize(n,u64)
    out += struct.pack("<QQQ",end,len(n.props),len(props)) if u64 else \
           struct.pack("<III",end,len(n.props),len(props))
    out += bytes([len(n.name)])+n.name+props
    for c in n.children: wnode(out,c,u64)
    if n.nullrec: out+=b"\x00"*NREC

def serialize(t):
    out=bytearray(t["header"])
    for n in t["top"]: wnode(out,n,t["u64"])
    if t["toplevel_null"]: out+=b"\x00"*(25 if t["u64"] else 13)
    out+=t["footer"]
    return bytes(out)


def walk(nodes):
    for n in nodes:
        yield n
        for x in walk(n.children): yield x

def donor_content(path):
    """The `Content` node of the donor's `Video`, with its raw payload."""
    t=parse(path)
    for n in walk(t["top"]):
        if n.name!=b"Video": continue
        for c in n.children:
            if c.name==b"Content" and c.props and c.props[0][0]=="R" and len(c.props[0][1])>64:
                return c
    raise SystemExit("donor has no Video/Content: "+path)

def graft(path, content):
    """Insert a copy of `content` into every Video node that lacks one."""
    t=parse(path); added=0
    for n in walk(t["top"]):
        if n.name!=b"Video": continue
        if any(c.name==b"Content" for c in n.children): continue
        c=Node(b"Content"); c.props=list(content.props); c.nullrec=content.nullrec
        # sits after RelativeFilename, which is where every embedding export puts it
        idx=max((i for i,ch in enumerate(n.children)
                 if ch.name in (b"RelativeFilename", b"Filename")), default=len(n.children)-1)
        n.children.insert(idx+1, c); added+=1
    return added, serialize(t)


if __name__=="__main__":
    a=sys.argv[1:]
    if a and a[0]=="--selftest":
        ok=True
        for f in a[1:]:
            t=parse(f); same=serialize(t)==t["orig"]; ok&=same
            print("  %-30s identical=%s  (%d bytes)"%(os.path.basename(f),same,len(t["orig"])))
        sys.exit(0 if ok else 1)
    if a and a[0]=="--donor":
        content=donor_content(a[1])
        print("donor blob: %d bytes"%len(content.props[0][1]))
        for f in a[2:]:
            t=parse(f)
            assert serialize(t)==t["orig"], "round trip failed, refusing to edit "+f
            n,data=graft(f, content)
            tmp=f+".tmp"
            open(tmp,"wb").write(data)
            os.replace(tmp, f)          # replaces the name, leaves other hardlinks alone
            print("  %-30s +%d Content  %d -> %d bytes"%(os.path.basename(f),n,len(t["orig"]),len(data)))
        sys.exit(0)
    sys.exit(__doc__)