same mesh, but different rendering result when using different texture type

[lcc815]

Summary

System configuration

System information:

CPU: AMD EPYC 7542 32-Core Processor
GPU: NVIDIA GeForce RTX 4090
Python: 3.8.13 (default, Apr 19 2022, 00:53:22) [GCC 7.5.0]
NVidia driver: 535.129.03
LLVM: 10.0.0

Dr.Jit: 0.4.6
Mitsuba: 3.5.2
Is custom build? False
Compiled with: GNU 10.2.1
Variants:
scalar_rgb
scalar_spectral
cuda_ad_rgb
llvm_ad_rgb

Description

I render two meshes. Their vertices & faces are completely the same, except that one is vertex-colored and the other is texture-mapped.
If open them in meshlab, they look the same.
However, I rendered them by mitsuba but got different result.
(1) the texture-mapped rendering result:

(2) the vertex-colored rendering result:

Everything of the scene keeps the same except the shape(e.g. the mesh). Also I divided the vertex color values by 255 to map it from 0-255 to 0-1.

Steps to reproduce

issue.zip

1. download the data I attached, which contains:
   
2. simply run python main.py, which is:

import mitsuba as mi

mi.set_variant("llvm_ad_rgb")

from mitsuba.scalar_rgb import Transform4f as T


def update_vertex_color():
    pillar_raw = mi.load_dict({
        "type": "ply",
        "filename": "pillar_vertex_colored.ply",
        "face_normals": False,
        "to_world": mi.ScalarTransform4f().rotate([0, 0, 1], angle=10),
    })

    params = mi.traverse(pillar_raw)
    params['vertex_color'] = params['vertex_color'] / 255.
    params.update()
    pillar_raw.write_ply("pillar_vertex_colored_updated.ply")


def build_scene(shape):
    emitter = {
            'type': 'envmap',
            'filename': 'city.hdr',
            'to_world': T.rotate([1,0,0], 90),
        }

    integrator = {
        'type': 'direct',
        'shading_samples': 4
    }


    sensor = mi.load_dict({
        'type': 'orthographic',
        'to_world': mi.ScalarTransform4f().look_at(
            origin=[0, 0, 0],
            target=[1, 0, 0],
            up=[0, 0, 1]
        )
    })

    scene =  mi.load_dict({
            'type': 'scene',
            'integrator': integrator,
            'sensor': sensor,
            "emitter": emitter,
            'shape': shape,
            })
    return scene


if __name__ == "__main__":
    update_vertex_color()
    shape1 = {
            'type': 'ply',
            'filename': 'pillar_vertex_colored_updated.ply',                   
            'to_world': T.translate([5, 0, -1]).scale(0.2).rotate([1, 0, 0], 45),
            'bsdf':{
                'type': 'diffuse',
                'reflectance': {
                    'type': 'mesh_attribute',
                    'name': 'vertex_color'
                },
            }
        }
    shape2 = {
            'type': 'obj',
            'filename': 'pillar_texture_map/pillar_texture_map.obj',
            'to_world': T.translate([5, 0, -1]).scale(0.2).rotate([1, 0, 0], 45),
            'bsdf':{
                'type': 'diffuse',
                'reflectance': {
                    'type': 'bitmap',
                    'filename': 'pillar_texture_map/material_0.png'
                },
            }
        }
    scene1 = build_scene(shape1)
    scene2 = build_scene(shape2)
    image1 = mi.render(scene1, spp=128)
    image2 = mi.render(scene2, spp=128)
    mi.util.write_bitmap("vertex_render.png", image1)
    mi.util.write_bitmap("texture_map_render.png", image2)