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Compute smooth normals for gltf
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@balazsdukai
balazsdukai committed Jan 11, 2023
1 parent f084f92 commit 423ffd6
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Showing 3 changed files with 134 additions and 26 deletions.
142 changes: 118 additions & 24 deletions cjio/convert.py
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Original file line number Diff line number Diff line change
@@ -1,10 +1,14 @@
import math
from io import BytesIO
import json

from cjio import geom_help

import numpy as np

from cjio.geom_help import triangle_normal_weighted


def flatten(x):
result = []
for el in x:
Expand Down Expand Up @@ -162,6 +166,7 @@ def to_glb(cm, do_triangulate=True):

for theid in cm.j['CityObjects']:
forimax = []
normals_per_geom = []

if "geometry" in cm.j['CityObjects'][theid] and len(cm.j['CityObjects'][theid]['geometry']) != 0:

Expand All @@ -188,8 +193,14 @@ def to_glb(cm, do_triangulate=True):
matid = 9
material_ids.append(matid)

#----- computing vertex normals
# We are computing soft-shading, which means computing the weighted average
# normal for each vertex.
# http://wiki.polycount.com/w/images/e/e5/FrostSoft_doc-3.png

if do_triangulate:
for geom in cm.j['CityObjects'][theid]['geometry']:
normals_per_vertex = {i: [] for i in range(len(vertexlist))}
poscount = poscount + 1
if geom['type'] == "Solid":
triList = []
Expand All @@ -199,6 +210,12 @@ def to_glb(cm, do_triangulate=True):
if success:
for t in tri:
triList.append(list(t))
# for gltf, we need to invert the vector
tri_normal = triangle_normal_weighted(t,
vertexlist) * -1.0
normals_per_vertex[t[0]].append(tri_normal)
normals_per_vertex[t[1]].append(tri_normal)
normals_per_vertex[t[2]].append(tri_normal)
else:
# TODO: logging
print(f"Failed to triangulate face in CityObject {theid}")
Expand All @@ -210,22 +227,45 @@ def to_glb(cm, do_triangulate=True):
tri, success = geom_help.triangulate_face(face, vertexlist)
if success:
for t in tri:
triList.append(t)
triList.append(list(t))
tri_normal = triangle_normal_weighted(t, vertexlist) * -1.0
normals_per_vertex[t[0]].append(tri_normal)
normals_per_vertex[t[1]].append(tri_normal)
normals_per_vertex[t[2]].append(tri_normal)
else:
# TODO: logging
print(f"Failed to triangulate face in CityObject {theid}")
trigeom = (flatten(triList))

forimax.append(trigeom)
# Computing smooth-shading (smooth-normal) for a vertex, as the sum of
# normals weighted by the triangle area of the adjacent triangles.
normals_per_vertex_smooth = {i: None for i in
range(len(vertexlist))}
for v, normals in normals_per_vertex.items():
s = sum(normals)
norm = 1.0 if math.isclose(n, 0.0) else n
normals_per_vertex_smooth[v] = s / norm
del normals_per_vertex
normals_per_geom.append(
list(normals_per_vertex_smooth[v] for v in trigeom))
else:
# If the caller says it's triangulate, then we trust that it's
# triangulated.
for geom in cm.j['CityObjects'][theid]['geometry']:
normals_per_vertex = {i: [] for i in range(len(vertexlist))}
poscount = poscount + 1
if geom['type'] == "Solid":
triList = []
for shell in geom['boundaries']:
for face in shell:
for t in face:
triList.append(list(t))
triList.append(t)
tri_normal = triangle_normal_weighted(t, vertexlist) * -1.0
normals_per_vertex[t[0]].append(tri_normal)
normals_per_vertex[t[1]].append(tri_normal)
normals_per_vertex[t[2]].append(tri_normal)

trigeom = (flatten(triList))

elif (geom['type'] == 'MultiSurface') or (
Expand All @@ -234,22 +274,44 @@ def to_glb(cm, do_triangulate=True):
for face in geom['boundaries']:
for t in face:
triList.append(t)
tri_normal = triangle_normal_weighted(t, vertexlist) * -1.0
normals_per_vertex[t[0]].append(tri_normal)
normals_per_vertex[t[1]].append(tri_normal)
normals_per_vertex[t[2]].append(tri_normal)
trigeom = (flatten(triList))
flatgeom = trigeom
forimax.append(flatgeom)

#----- buffer and bufferView
forimax.append(trigeom)
# Computing smooth-shading (smooth-normal) for a vertex, as the sum of
# normals weighted by the triangle area of the adjacent triangles.
normals_per_vertex_smooth = {i: None for i in
range(len(vertexlist))}
for v, normals in normals_per_vertex.items():
s = sum(normals)
n = np.linalg.norm(s)
norm = 1.0 if math.isclose(n, 0.0) else n
normals_per_vertex_smooth[v] = s / norm
del normals_per_vertex
normals_per_geom.append(list(normals_per_vertex_smooth[v] for v in trigeom))

# Flatten the triangle-vertex lists for each CityObject geometry into a
# single list. Each consecutive set of three vertices defines a
# single triangle primitive.
flatgeom = flatten(forimax)
# Same for the normal-vertex lists
normals_np = np.concatenate(normals_per_geom)
if len(normals_np) != len(flatgeom):
raise RuntimeError("The length of vertices and normals should be equal")
del normals_per_geom

#----- buffer and bufferView
# allocate for vertex coordinates
vtx_np = np.zeros((len(flatgeom), 3))
# allocate for vertex indices
vtx_idx_np = np.zeros(len(flatgeom))
# need to reindex the vertices, otherwise if the vtx index exceeds the nr. of vertices in the
# accessor then we get "ACCESSOR_INDEX_OOB" error
for i,v in enumerate(flatgeom):
# Need to swap the axis, because gltf uses a right-handed coordinate
# system. glTF defines +Y as up, +Z as forward, and -X as right;
# the front of a glTF asset faces +Z.
try:
# vtx_np[i] = np.array((vertexlist[v][1], vertexlist[v][2], vertexlist[v][0]))
vtx_np[i] = np.array(
(vertexlist[v][0], vertexlist[v][1], vertexlist[v][2]))
except IndexError as e:
Expand All @@ -258,6 +320,9 @@ def to_glb(cm, do_triangulate=True):
bin_vtx = vtx_np.astype(np.float32).tostring()
# convert geometry indices to binary
bin_geom = vtx_idx_np.astype(np.uint32).tostring()
del flatgeom
# convert the normal to binary
bin_normals = normals_np.astype(np.float32).tostring()
# convert batchid to binary
batchid_np = np.array([i for g in vtx_idx_np])
bin_batchid = batchid_np.astype(np.uint32).tostring()
Expand All @@ -275,34 +340,48 @@ def to_glb(cm, do_triangulate=True):
gltf_bin.extend(bytearray(padding))
bufferViews.append(bufferView)

#-- geometry vertices bufferView
#-- geometry vertices (POSITION) bufferView
bpos = len(gltf_bin)
offset, padding = byte_offset(bpos, 4)
bufferView = dict()
bufferView["buffer"] = 0
bufferView["byteOffset"] = offset
bufferView["byteStride"] = 12
# bufferView["byteStride"] = 12
bufferView["byteLength"] = len(bin_vtx)
bufferView["target"] = 34962
# write to the buffer
gltf_bin.extend(bin_vtx)
gltf_bin.extend(bytearray(padding))
bufferViews.append(bufferView)

#-- batchid bufferView
#-- vertex normals (NORMAL) bufferView
bpos = len(gltf_bin)
offset, padding = byte_offset(bpos, 4)
bufferView = dict()
bufferView["buffer"] = 0
bufferView["byteOffset"] = offset
bufferView["byteStride"] = 4
bufferView["byteLength"] = len(bin_batchid)
# bufferView["byteStride"] = 12
bufferView["byteLength"] = len(bin_normals)
bufferView["target"] = 34962
# write to the buffer
gltf_bin.extend(bin_batchid)
gltf_bin.extend(bin_normals)
gltf_bin.extend(bytearray(padding))
bufferViews.append(bufferView)

# #-- batchid bufferView
# bpos = len(gltf_bin)
# offset, padding = byte_offset(bpos, 4)
# bufferView = dict()
# bufferView["buffer"] = 0
# bufferView["byteOffset"] = offset
# bufferView["byteStride"] = 4
# bufferView["byteLength"] = len(bin_batchid)
# bufferView["target"] = 34962
# # write to the buffer
# gltf_bin.extend(bin_batchid)
# gltf_bin.extend(bytearray(padding))
# bufferViews.append(bufferView)

# ----- accessors

# accessor for geometry indices bufferView
Expand All @@ -318,12 +397,12 @@ def to_glb(cm, do_triangulate=True):
accessor["min"] = [int(vtx_idx_np.min())]
accessors.append(accessor)

# accessor for geometry vertices bufferView
# accessor for geometry vertices (POSITION) bufferView
accessor = dict()
# without an empty root node we would need = 1 if coi_node_idx == 0 else coi_node_idx * 3 + 1
accessor["bufferView"] = mesh_idx * 3 + 1
accessor["componentType"] = 5126
accessor["count"] = int(vtx_idx_np.size)
accessor["count"] = len(vtx_np)
accessor["type"] = "VEC3"
accessor["max"] = [float(np.amax(vtx_np, axis=0)[0]),
float(np.amax(vtx_np, axis=0)[1]),
Expand All @@ -333,15 +412,29 @@ def to_glb(cm, do_triangulate=True):
float(np.amin(vtx_np, axis=0)[2])]
accessors.append(accessor)

# accessor for batchid bufferView
# accessor for vertex normals (NORMAL) bufferView
accessor = dict()
# without an empty root node we would need = 2 if coi_node_idx == 0 else coi_node_idx * 3 + 2
accessor["bufferView"] = mesh_idx * 3 + 2
accessor["componentType"] = 5123
accessor["count"] = int(vtx_idx_np.size)
accessor["type"] = "SCALAR"
accessor["componentType"] = 5126
accessor["count"] = len(normals_np)
accessor["type"] = "VEC3"
accessor["max"] = [float(np.amax(normals_np, axis=0)[0]),
float(np.amax(normals_np, axis=0)[1]),
float(np.amax(normals_np, axis=0)[2])]
accessor["min"] = [float(np.amin(normals_np, axis=0)[0]),
float(np.amin(normals_np, axis=0)[1]),
float(np.amin(normals_np, axis=0)[2])]
accessors.append(accessor)

# # accessor for batchid bufferView
# accessor = dict()
# # without an empty root node we would need = 2 if coi_node_idx == 0 else coi_node_idx * 3 + 2
# accessor["bufferView"] = mesh_idx * 3 + 3
# accessor["componentType"] = 5123
# accessor["count"] = len(batchid_np)
# accessor["type"] = "SCALAR"
# accessors.append(accessor)

# ----- meshes
# one mesh per CityObject
mesh = dict()
Expand All @@ -350,7 +443,8 @@ def to_glb(cm, do_triangulate=True):
"indices": len(accessors) - 3,
"material": matid,
"attributes": {
"_BATCHID": len(accessors) - 1,
# "_BATCHID": len(accessors) - 1,
"NORMAL": len(accessors) - 1,
"POSITION": len(accessors) - 2,
}
}]
Expand Down Expand Up @@ -389,7 +483,7 @@ def to_glb(cm, do_triangulate=True):
"pbrMetallicRoughness": {
"baseColorFactor": [0.7200, 0.320, 0.220, 1.0],
"metallicFactor": 0.0,
"roughnessFactor": 0.0
"roughnessFactor": 1.0
}
},
{ # terrain brown
Expand Down
16 changes: 15 additions & 1 deletion cjio/geom_help.py
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Original file line number Diff line number Diff line change
Expand Up @@ -191,4 +191,18 @@ def triangulate_face_mapbox_earcut(face, vnp):
result[i] = sf[each]

# print (result.reshape(-1, 3))
return (result.reshape(-1, 3), True)
return (result.reshape(-1, 3), True)


def triangle_normal_weighted(tri, vertexlist):
"""Compute the triangle normal vector weighted by the triangle area."""
v0, v1, v2 = tri[0], tri[1], tri[2]
p0 = np.array((vertexlist[v0][0], vertexlist[v0][1], vertexlist[v0][2]))
p1 = np.array((vertexlist[v1][0], vertexlist[v1][1], vertexlist[v1][2]))
p2 = np.array((vertexlist[v2][0], vertexlist[v2][1], vertexlist[v2][2]))
cross_prod = np.cross(p1 - p0, p2 - p0)
m = np.linalg.norm(cross_prod)
magnitude = 1.0 if math.isclose(m, 0) else m
norm_vec = cross_prod / magnitude
tri_area = magnitude * 0.5
return norm_vec * tri_area
2 changes: 1 addition & 1 deletion tests/test_convert.py
View file
Original file line number Diff line number Diff line change
Expand Up @@ -31,7 +31,7 @@ def test_debug_delft_glb(self, data_dir, data_output_dir):
p = os.path.join(data_dir, "0-1.city.json")
with open(p, 'r') as f:
cm = cityjson.CityJSON(file=f)
glb = cm.export2glb()
glb = cm.export2glb(do_triangulate=False)
glb.seek(0)
with open(f"{data_output_dir}/0-1.glb", mode='wb') as bo:
bo.write(glb.getvalue())
Expand Down

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