98 lines
3.8 KiB
Python
98 lines
3.8 KiB
Python
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"""Pure-python linear-blend skinning check: skin a GLB's verts with its current node TRS
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(what Godot would render) and report max displacement of finger-weighted verts vs the
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original file. usage: skin_check.py posed.glb original.glb"""
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import json, struct, sys, math
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from pathlib import Path
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FING = ("thumb", "index", "middle", "ring", "pinky")
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def read_glb(path):
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d = Path(path).read_bytes()
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length = struct.unpack_from("<I", d, 8)[0]
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off = 12; g = None; b = None
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while off < length:
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clen, ct = struct.unpack_from("<II", d, off); off += 8
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if ct == 0x4E4F534A: g = json.loads(d[off:off+clen])
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else: b = d[off:off+clen]
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off += clen
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return g, b
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def acc(g, b, i):
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a = g["accessors"][i]; bv = g["bufferViews"][a["bufferView"]]
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nc = {"SCALAR":1,"VEC2":2,"VEC3":3,"VEC4":4,"MAT4":16}[a["type"]]
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fmt = {5121:"B",5123:"H",5125:"I",5126:"f"}[a["componentType"]]
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size = struct.calcsize(fmt)*nc; stride = bv.get("byteStride") or size
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off = bv.get("byteOffset",0)+a.get("byteOffset",0)
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return [struct.unpack_from("<%d%s"%(nc,fmt), b, off+i*stride) for i in range(a["count"])], a["componentType"]
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def quat_mat(q):
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x,y,z,w = q
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return [[1-2*(y*y+z*z),2*(x*y-z*w),2*(x*z+y*w)],
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[2*(x*y+z*w),1-2*(x*x+z*z),2*(y*z-x*w)],
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[2*(x*z-y*w),2*(y*z+x*w),1-2*(x*x+y*y)]]
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def node_local(nd):
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t = nd.get("translation",[0,0,0]); r = nd.get("rotation",[0,0,0,1]); s = nd.get("scale",[1,1,1])
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R = quat_mat(r)
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M = [[R[i][j]*s[j] for j in range(3)]+[t[i]] for i in range(3)]
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return M+[[0,0,0,1]]
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def matmul(A,B):
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return [[sum(A[i][k]*B[k][j] for k in range(4)) for j in range(4)] for i in range(4)]
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def globals_(g):
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loc = [node_local(nd) for nd in g["nodes"]]
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parent = {}
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for i,nd in enumerate(g["nodes"]):
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for c in nd.get("children",[]): parent[c] = i
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memo = {}
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def gm(i):
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if i in memo: return memo[i]
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m = loc[i] if i not in parent else matmul(gm(parent[i]), loc[i])
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memo[i] = m; return m
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return [gm(i) for i in range(len(g["nodes"]))]
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def skinned_positions(g, b, only_finger=True):
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names = [nd.get("name","") for nd in g["nodes"]]
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G = globals_(g)
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skin = g["skins"][0]
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joints = skin["joints"]
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ibm, _ = acc(g, b, skin["inverseBindMatrices"])
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# glTF matrices are column-major
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def m16(row):
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return [[row[c*4+r] for c in range(4)] for r in range(4)]
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JM = [matmul(G[joints[j]], m16(ibm[j])) for j in range(len(joints))]
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prim = g["meshes"][0]["primitives"][0]
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P,_ = acc(g,b,prim["attributes"]["POSITION"])
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J,_ = acc(g,b,prim["attributes"]["JOINTS_0"])
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W,wt = acc(g,b,prim["attributes"]["WEIGHTS_0"])
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wsc = 1.0 if wt==5126 else (1/255 if wt==5121 else 1/65535)
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out = {}
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for vi,(p,jr,wr) in enumerate(zip(P,J,W)):
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if only_finger and not any(any(t in names[joints[j]].lower() for t in FING)
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for j,w in zip(jr,wr) if w>0):
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continue
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x=y=z=0.0
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for j,w in zip(jr,wr):
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w*=wsc
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if w<=0: continue
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M=JM[j]
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x+=w*(M[0][0]*p[0]+M[0][1]*p[1]+M[0][2]*p[2]+M[0][3])
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y+=w*(M[1][0]*p[0]+M[1][1]*p[1]+M[1][2]*p[2]+M[1][3])
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z+=w*(M[2][0]*p[0]+M[2][1]*p[1]+M[2][2]*p[2]+M[2][3])
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out[vi]=(x,y,z)
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return out, names, joints
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posed_g, posed_b = read_glb(sys.argv[1])
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orig_g, orig_b = read_glb(sys.argv[2])
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a, names, joints = skinned_positions(posed_g, posed_b)
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c, _, _ = skinned_positions(orig_g, orig_b)
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dmax = 0; worst = None
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for vi in a:
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d = math.dist(a[vi], c[vi])
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if d > dmax: dmax, worst = d, vi
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print(f"finger-weighted verts: {len(a)}; max displacement posed-vs-original: {dmax*100:.1f} cm (vert {worst})")
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import statistics
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ds = sorted(math.dist(a[vi], c[vi]) for vi in a)
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print(f"median: {ds[len(ds)//2]*100:.2f} cm, p95: {ds[int(len(ds)*0.95)]*100:.2f} cm")
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