Regression: Mesh method from_pydata in Python API does not work with quads and tris #111117

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opened 2023-08-14 16:26:08 +02:00 by Alexander Milovsky · 5 comments

Alexander Milovsky commented

2023-08-14 16:26:08 +02:00

System Information
Operating system: Windows-10-10.0.22621-SP0 64 Bits
Graphics card: GeForce GTX 1050/PCIe/SSE2 NVIDIA Corporation 4.6.0 NVIDIA 442.19

Blender Version
Broken: version: 4.0.0 Alpha, branch: main, commit date: 2023-08-14 04:21, hash: deb4aa88b04a
Worked: 3.6.1

Caused by a280e8a68c

Short description of error
Mesh method from_pydata in Python API does not work on polygons with variable vertex count (quads and tris for example)

Exact steps for others to reproduce the error
Put this Python-code into the Console on the Scripting tab:

import bpy
vertices = [(0, 0, 0), (1, 0, 0), (2, 0, 0), (0, 1, 0), (1, 1, 0), (2, 1, 0)]
faces = [(0, 1, 4, 3), (1, 2, 5)]  # two polygons: quad and tris

mesh = bpy.data.meshes.new('test_mesh')
mesh.from_pydata(vertices, [], faces)  # produces error in Blender 4.0 Alpha
mesh.update()

obj = bpy.data.objects.new('test_obj', mesh)
bpy.context.scene.collection.objects.link(obj)

**System Information** Operating system: Windows-10-10.0.22621-SP0 64 Bits Graphics card: GeForce GTX 1050/PCIe/SSE2 NVIDIA Corporation 4.6.0 NVIDIA 442.19 **Blender Version** Broken: version: 4.0.0 Alpha, branch: main, commit date: 2023-08-14 04:21, hash: `deb4aa88b04a` Worked: 3.6.1 Caused by a280e8a68c **Short description of error** Mesh method from_pydata in Python API does not work on polygons with variable vertex count (quads and tris for example) **Exact steps for others to reproduce the error** Put this Python-code into the Console on the Scripting tab: ```Py import bpy vertices = [(0, 0, 0), (1, 0, 0), (2, 0, 0), (0, 1, 0), (1, 1, 0), (2, 1, 0)] faces = [(0, 1, 4, 3), (1, 2, 5)] # two polygons: quad and tris mesh = bpy.data.meshes.new('test_mesh') mesh.from_pydata(vertices, [], faces) # produces error in Blender 4.0 Alpha mesh.update() obj = bpy.data.objects.new('test_obj', mesh) bpy.context.scene.collection.objects.link(obj) ```

Alexander Milovsky added the

labels 2023-08-14 16:26:08 +02:00

Iliya Katushenock added the

labels 2023-08-14 16:28:28 +02:00

Iliya Katushenock changed title from ~~Mesh method from_pydata in Python API does not work with quads and tris~~ to Regression: Mesh method from_pydata in Python API does not work with quads and tris

2023-08-14 16:28:35 +02:00

Thomas Barlow commented

2023-08-14 22:26:02 +02:00

Member

I think this may be the same issue as blender/blender-addons#104762.

I'm of the opinion this is a bug with Blender though:

The raised error is:

Error: Python: Traceback (most recent call last):
  File "\Text", line 85, in <module>
  File "D:\Downloads\temp\blender-4.0.0-alpha+main.aebc743bf1c7-windows.amd64-release\4.0\scripts\modules\bpy_types.py", line 627, in from_pydata
    self.polygons.foreach_set("vertices", vertex_indices)
TypeError: foreach_get(attr, sequence) sequence length mismatch given 7, needed 8

I copied the from_pydata function and added some print statements directly before the line that raises the TypeError.

    print(len(self.loops))
    print(loop_starts)
    for p in mesh.polygons:
        print(p.loop_total)
        print(len(p.vertices))
    self.polygons.foreach_set("vertices", vertex_indices)

This prints

So individually, it seems to me that 7 is the length Blender should be checking for and that Blender saying it should be 8 is incorrect.

I guess the changes in a280e8a68c might have identified an issue with using foreach_set with MeshPolygon.vertices that has been present but unnoticed for some time.

In this case, as a workaround, it works if I replace
self.polygons.foreach_set("vertices", vertex_indices)
with
self.loops.foreach_set("vertex_index", vertex_indices)
because polygons and loops (corners) are now always in the same order. So long as the mesh is valid (every loop belongs to exactly one polygon and every polygon's loop_start is in-bounds), MeshPolygon.vertices accessed through foreach_set is effectively a shortcut for iterating through the mesh's loops and setting each loop's vertex_index.

New script with comments:

import bpy
vertices = [(0, 0, 0), (1, 0, 0), (2, 0, 0), (0, 1, 0), (1, 1, 0), (2, 1, 0)]
faces = [(0, 1, 4, 3), (1, 2, 5)]  # two polygons: quad and tris


def from_pydata(self, vertices, edges, faces, shade_flat=True):
    from itertools import chain, islice, accumulate

    face_lengths = tuple(map(len, faces))

    # NOTE: check non-empty lists by length because of how `numpy` handles truth tests, see: #90268.
    vertices_len = len(vertices)
    edges_len = len(edges)
    faces_len = len(faces)

    self.vertices.add(vertices_len)
    self.edges.add(edges_len)
    self.loops.add(sum(face_lengths))
    self.polygons.add(faces_len)

    self.vertices.foreach_set("co", tuple(chain.from_iterable(vertices)))
    self.edges.foreach_set("vertices", tuple(chain.from_iterable(edges)))

    vertex_indices = tuple(chain.from_iterable(faces))
    loop_starts = tuple(islice(chain([0], accumulate(face_lengths)), faces_len))

    self.polygons.foreach_set("loop_start", loop_starts)
    
    print(len(self.loops))
    print(loop_starts)
    for p in self.polygons:
        print(p.loop_total)
        print(len(p.vertices))
    
    # Error occurs
    self.polygons.foreach_set("vertices", vertex_indices)
    # If the mesh is valid, using foreach_set with MeshPolygon.vertices is effectively the
    # same as using foreach_set with MeshLoop.vertex_index
    #self.loops.foreach_set("vertex_index", vertex_indices)

    if shade_flat:
        self.shade_flat()

    if edges_len or faces_len:
        self.update(
            # Needed to either:
            # - Calculate edges that don't exist for polygons.
            # - Assign edges to polygon loops.
            calc_edges=bool(faces_len),
            # Flag loose edges.
            calc_edges_loose=bool(edges_len),
        )


mesh = bpy.data.meshes.new('test_mesh')
from_pydata(mesh, vertices, [], faces)

I think this may be the same issue as https://projects.blender.org/blender/blender-addons/issues/104762. I'm of the opinion this is a bug with Blender though: The raised error is: ``` Error: Python: Traceback (most recent call last): File "\Text", line 85, in <module> File "D:\Downloads\temp\blender-4.0.0-alpha+main.aebc743bf1c7-windows.amd64-release\4.0\scripts\modules\bpy_types.py", line 627, in from_pydata self.polygons.foreach_set("vertices", vertex_indices) TypeError: foreach_get(attr, sequence) sequence length mismatch given 7, needed 8 ``` I copied the `from_pydata` function and added some print statements directly before the line that raises the `TypeError`. ```py print(len(self.loops)) print(loop_starts) for p in mesh.polygons: print(p.loop_total) print(len(p.vertices)) self.polygons.foreach_set("vertices", vertex_indices) ``` This prints ``` 7 (0, 4) 4 4 3 3 ``` So individually, it seems to me that 7 is the length Blender should be checking for and that Blender saying it should be 8 is incorrect. I guess the changes in https://projects.blender.org/blender/blender/commit/a280e8a68c15ee3ec0978fb594b29d083fd2bcd6 might have identified an issue with using `foreach_set` with `MeshPolygon.vertices` that has been present but unnoticed for some time. In this case, as a workaround, it works if I replace `self.polygons.foreach_set("vertices", vertex_indices)` with `self.loops.foreach_set("vertex_index", vertex_indices)` because polygons and loops (corners) are now always in the same order. So long as the mesh is valid (every loop belongs to exactly one polygon and every polygon's `loop_start` is in-bounds), `MeshPolygon.vertices` accessed through `foreach_set` is effectively a shortcut for iterating through the mesh's loops and setting each loop's `vertex_index`. New script with comments: ```py import bpy vertices = [(0, 0, 0), (1, 0, 0), (2, 0, 0), (0, 1, 0), (1, 1, 0), (2, 1, 0)] faces = [(0, 1, 4, 3), (1, 2, 5)] # two polygons: quad and tris def from_pydata(self, vertices, edges, faces, shade_flat=True): from itertools import chain, islice, accumulate face_lengths = tuple(map(len, faces)) # NOTE: check non-empty lists by length because of how `numpy` handles truth tests, see: #90268. vertices_len = len(vertices) edges_len = len(edges) faces_len = len(faces) self.vertices.add(vertices_len) self.edges.add(edges_len) self.loops.add(sum(face_lengths)) self.polygons.add(faces_len) self.vertices.foreach_set("co", tuple(chain.from_iterable(vertices))) self.edges.foreach_set("vertices", tuple(chain.from_iterable(edges))) vertex_indices = tuple(chain.from_iterable(faces)) loop_starts = tuple(islice(chain([0], accumulate(face_lengths)), faces_len)) self.polygons.foreach_set("loop_start", loop_starts) print(len(self.loops)) print(loop_starts) for p in self.polygons: print(p.loop_total) print(len(p.vertices)) # Error occurs self.polygons.foreach_set("vertices", vertex_indices) # If the mesh is valid, using foreach_set with MeshPolygon.vertices is effectively the # same as using foreach_set with MeshLoop.vertex_index #self.loops.foreach_set("vertex_index", vertex_indices) if shade_flat: self.shade_flat() if edges_len or faces_len: self.update( # Needed to either: # - Calculate edges that don't exist for polygons. # - Assign edges to polygon loops. calc_edges=bool(faces_len), # Flag loose edges. calc_edges_loose=bool(edges_len), ) mesh = bpy.data.meshes.new('test_mesh') from_pydata(mesh, vertices, [], faces) ```

Germano Cavalcante commented

2023-08-15 00:44:21 +02:00

Member

I can confirm the problem, and indeed it is the same as blender/blender-addons#104762

However, since this report is in the repository that contains the affected code, I'm confirming it here.

It is caused by a280e8a68c. That commit does the size check based only on the size of the first element. So in the case of polygons in this report, the value will be 2 * 4 (number of faces multiplied by the number of vertices of the first face).

To fix the check, it would be necessary to sum the size of each individual element. But this can penalize the performance of the foreach function.

Maybe a280e8a68c has to be reverted for now :\

Cc @Baardaap, @lichtwerk

I can confirm the problem, and indeed it is the same as blender/blender-addons#104762 However, since this report is in the repository that contains the affected code, I'm confirming it here. It is caused by a280e8a68c. That commit does the size check based only on the size of the first element. So in the case of polygons in this report, the value will be 2 * 4 (number of faces multiplied by the number of vertices of the first face). To fix the check, it would be necessary to sum the size of each individual element. But this can penalize the performance of the `foreach` function. Maybe a280e8a68c has to be reverted for now :\ Cc @Baardaap, @lichtwerk

Germano Cavalcante added

and removed

labels 2023-08-15 00:45:17 +02:00

Germano Cavalcante referenced this issue from blender/blender-addons

2023-08-15 00:47:33 +02:00

in 4.0 alpha, i cannot add bolts anymore... #104762

Philipp Oeser commented

2023-08-15 11:11:32 +02:00

Member

Will summon reviewers of #109179 here to discuss...

CC @brecht
CC @HooglyBoogly

Will summon reviewers of https://projects.blender.org/blender/blender/pulls/109179 here to discuss... CC @brecht CC @HooglyBoogly

Hans Goudey commented

2023-08-15 14:10:38 +02:00

Member

The fix proposed of just setting the corner vertex indices seems right to me in theory, thanks for looking into this.

The fix proposed of just setting the corner vertex indices seems right to me in theory, thanks for looking into this.

Martijn Versteegh commented

2023-08-26 22:27:36 +02:00

Member

I can maybe partially revert a280e8a68c. Just revert the check causing the problem and not the added code which is needed to fix #107416

I can maybe partially revert a280e8a68c. Just revert the check causing the problem and not the added code which is needed to fix #107416

Pratik Borhade referenced this issue from blender/blender-addons

2023-09-07 10:36:42 +02:00

Blender 4.0 alpha - Add-on Archimesh doesn't work in most parts #104743

Martijn Versteegh referenced a pull request that will close this issue

2023-09-25 23:32:15 +02:00

Fix #111117: Partially revert a280e8a6 #112879

Martijn Versteegh referenced this issue from blender/blender-addons

2023-10-01 00:17:10 +02:00

Blender 4.0 alpha - Add-on Archimesh doesn't work in most parts #104743

Martijn Versteegh referenced this issue from a commit

2023-10-01 00:17:57 +02:00

Fix #111117: Partially revert a280e8a6

Martijn Versteegh closed this issue

2023-10-01 00:17:58 +02:00

Blender Bot added

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labels 2023-10-01 00:18:00 +02:00

~~Campbell Barton referenced this issue 2023-10-01 05:12:58 +02:00~~

Blender LTS: Maintenance Task 3.6 #109399

Campbell Barton referenced this issue from a commit

2023-10-01 05:23:31 +02:00

Follow up to fix for #111117, remove array/collection length lookup

Jesse Yurkovich referenced this issue from blender/blender-addons

2023-10-01 10:56:09 +02:00

Bolt Factory #104929

Joseph Eagar referenced this issue from a commit

2023-10-07 21:46:16 +02:00

Fix #111117: Partially revert a280e8a6

Joseph Eagar referenced this issue from a commit

2023-10-07 21:46:16 +02:00

Follow up to fix for #111117, remove array/collection length lookup

Joseph Eagar referenced this issue from a commit

2023-10-07 21:46:17 +02:00

Fix #111117: Partially revert a280e8a6

Joseph Eagar referenced this issue from a commit

2023-10-07 21:46:17 +02:00

Follow up to fix for #111117, remove array/collection length lookup

Brecht Van Lommel referenced this issue

2023-11-13 14:56:45 +01:00

Blender LTS: Maintenance Task 3.6 #109399

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