glTF ring

References

• glb

• mesh

• Cinematic rendering

A jewellery model read from a Draco-compressed .glb and path traced. The stones are mesh objects with transmission=1, an index of refraction of 2.09 and a thickness, read from the file’s KHR_materials_transmission, KHR_materials_ior and KHR_materials_volume. The thickness is what makes them solid: without it glTF reads a transmissive surface as a thin wall that light crosses almost unbent, like a window. Here light enters the stones, bends, and bounces between the facets before it leaves, which is why the renderer gets 32 bounces rather than the default. The floor under the ring is what catches its shadow and the light it throws back.

Every part keeps the name of its glTF material in custom_data, so the parts that share a material are found by that name and changed like any other object - here the band, pushed towards rose gold and polished.

Reading Draco-compressed geometry needs DracoPy (pip install DracoPy); everything else k3d.glb() reads with numpy alone.

sasha.glb - converted from the original .blend as assets/sasha.md describes.

import numpy as np

import k3d

# Model: "Sasha" by saber7711 on Blendswap (https://blendswap.com/blend/29574), CC-BY,
# converted to glTF for these docs
filename = 'sasha.glb'

ring = k3d.glb(filename, rotation=[np.pi / 4, 0, -1, 0], compression_level=9)


def lerp_color(a, b, t):
    ca = np.array([(a >> 16) & 255, (a >> 8) & 255, a & 255], float)
    cb = np.array([(b >> 16) & 255, (b >> 8) & 255, b & 255], float)
    r, g, b_ = np.rint(ca + (cb - ca) * t).astype(int)
    return int((r << 16) | (g << 8) | b_)


for part in ring:
    if part.custom_data.get('gltf_material') == 'Material.002':
        part.color = lerp_color(part.color, 0xC47258, 0.45)
        part.roughness = 0.05

boxes = np.array([part.get_bounding_box() for part in ring])
low, high = boxes[:, 0::2].min(axis=0), boxes[:, 1::2].max(axis=0)
centre = (low + high) / 2
size = float((high - low).max())

plot = k3d.plot(renderer='cinematic',
                environment='brown_photostudio_02',
                tone_mapping='aces',
                lighting=2.0,
                grid_visible=False,
                camera_auto_fit=False,
                background_color=0xE6E6E6,
                camera_fov=30,
                cinematic_samples=32,
                cinematic_denoise=1.0,
                cinematic_bounces=32)
plot += ring

span = 3 * size
floor = float(low[2])
plot += k3d.mesh(np.array([[centre[0] - span, centre[1] - span, floor],
                           [centre[0] + span, centre[1] - span, floor],
                           [centre[0] + span, centre[1] + span, floor],
                           [centre[0] - span, centre[1] + span, floor]], np.float32),
                 np.array([[0, 1, 2], [0, 2, 3]], np.uint32),
                 color=0xF2F2F2, roughness=0.5, name='floor')

# a glowing panel overhead, out of frame: the light the stones sparkle with
top = float(high[2]) + 1.5 * size
plot += k3d.mesh(np.array([[centre[0] - size, centre[1] - size, top],
                           [centre[0] + size, centre[1] - size, top],
                           [centre[0] + size, centre[1] + size, top],
                           [centre[0] - size, centre[1] + size, top]], np.float32),
                 np.array([[0, 2, 1], [0, 3, 2]], np.uint32),
                 color=0x000000, emissive=0xFFFFFF, emissive_intensity=4.0, side='double',
                 name='light box')

gems = np.array([part.get_bounding_box() for part in ring if part.transmission > 0])
target = (gems[:, 0::2].min(axis=0) + gems[:, 1::2].max(axis=0)) / 2
out = target - centre
out[2] = 0
out /= np.linalg.norm(out)
side = np.cross([0, 0, 1], out)
eye = target + (0.9 * out - 0.75 * side + 1.0 * np.array([0, 0, 1])) * size
plot.camera = [*eye, *target, 0, 0, 1]

plot.display()