Transparent objects casting dark shadows

[LandonRieger]

This has been a great tool, thanks a lot for providing it. I'm having a minor issue with transparent objects casting shadows darker than I would expect. For example, if I set the opacity to zero, I would expect the object to essentially be invisible, but this isn't what I'm seeing. Below is an example of what I mean, adapted from one of the provided examples.

import numpy as np
from plotoptix import NpOptiX
from plotoptix.enums import Geometry
from plotoptix.materials import m_transparent_diffuse
import threading
import copy
from PIL import Image


class params:
    done = threading.Event()


def accum_done(rt: NpOptiX) -> None:
    params.done.set()


def main():

    rt = NpOptiX(on_rt_accum_done=accum_done, width=1000, height=300)
    rt.set_param(min_accumulation_step=500, max_accumulation_frames=500)

    # geometry setup
    box_size = 1.5
    panel_size = 1.0
    z = box_size + 0.1  # offset panels a bit in front of boxes
    spacing = (box_size - panel_size) / 2
    vertices = np.array([[0, 0, z], [0, panel_size, z], [panel_size, panel_size, z], [panel_size, 0, z]], np.float32)
    faces = np.array([[0, 1, 2], [2, 3, 0]])
    uvmap = np.array([[0, 0], [0, 1], [1, 1], [1, 0]], np.float32)
    pos = [[0, 0, 0]]  # add a box at origin with no panel in front

    # blueish panel in front of boxes with increasing opacity
    colors = np.ones((2, 2, 4), dtype=np.float32) * 0.5
    colors[:, :, 0] = 0.0
    alphas = [0.0, 0.02, 0.1, 0.5]

    # add the boxes and panels
    for idx, alpha in enumerate(alphas):

        colors[:, :, 3] = alpha
        rt.set_texture_2d(f"mesh_tex_{idx}", colors)

        mat = copy.deepcopy(m_transparent_diffuse)
        mat["ColorTextures"] = [f"mesh_tex_{idx}"]
        rt.setup_material(f"mesh_mat_{idx}", mat)

        x_pos = (idx + 1) * (box_size + spacing)
        rt.set_mesh(
            f"mesh_{idx}",
            pos=vertices + np.array([x_pos + spacing, spacing, 0.0], dtype=np.float32),
            faces=faces,
            uvmap=uvmap,
            mat=f"mesh_mat_{idx}",
        )
        pos.append([x_pos, 0.0, 0.0])

    rt.set_data(
        "plot", 
        geom=Geometry.ParallelepipedsConstSize, 
        pos=np.array(pos, dtype=np.float32), 
        r=box_size, 
        c=0.75
        )
    rt.set_ambient(0.9)

    x_camera = ((len(alphas) + 1) * (box_size + spacing)) / 2
    rt.setup_camera(
        name="camera1", 
        eye=[x_camera, box_size / 2, 10.0], 
        target=[x_camera, box_size / 2, 0], 
        fov=20
        )

    rt.start()

    if params.done.wait(10):
        print("frame 1 done")
    else:
        print("timeout")

    Image.fromarray(np.array(rt._raw_rgba * 255, dtype=np.uint8), mode="RGBA").save("frame_1.png")
    params.done.clear()
    rt.close()


if __name__ == "__main__":
    main()

[robertsulej]

OK, I see, I'll have a look and let you know.

[robertsulej]

The issue is with the normalization when tracing the occlusion. I did not solve it yet completely, fixing this case I get into problems with overlapping object... but will try more. For the moment, for this particular configuration, the glass-like transparent material might work for you:

This is interactive variant with gui. The glass material has the refraction index set to 1, so it behaves like a layer of air (no refractions and reflections on faces):

import numpy as np
from plotoptix import TkOptiX
from plotoptix.enums import Geometry
from plotoptix.materials import m_transparent_diffuse, m_clear_glass
import threading
import copy
from PIL import Image

def main():

    rt = TkOptiX(width=1000, height=300)
    rt.set_param(
        min_accumulation_step=32, max_accumulation_frames=512,
        light_shading="Hard"
    )
    rt.set_uint("path_seg_range", 6, 8)

    # geometry setup
    box_size = 1.5
    panel_size = 1.0
    z = box_size + 0.1  # offset panels a bit in front of boxes
    spacing = (box_size - panel_size) / 2
    vertices = np.array([[0, 0, z], [0, panel_size, z], [panel_size, panel_size, z], [panel_size, 0, z]], np.float32)
    faces = np.array([[0, 1, 2], [2, 3, 0]])
    uvmap = np.array([[0, 0], [0, 1], [1, 1], [1, 0]], np.float32)
    pos = [[0, 0, 0]]  # add a box at origin with no panel in front

    # blueish panel in front of boxes with increasing opacity
    colors = np.ones((2, 2, 4), dtype=np.float32) * 0.5
    colors[:, :, 0] = 0.0
    alphas = [0.0, 0.02, 0.1, 0.5]

    # add the boxes and panels
    for idx, alpha in enumerate(alphas):

        x_pos = (idx + 1) * (box_size + spacing)
        pos.append([x_pos, 0.0, 0.0])

    m_clear_glass["VarFloat3"]["refraction_index"] = [ 1., 1., 1. ]
    rt.setup_material("glass", m_clear_glass)
    panel_colors = np.ones((5, 3), dtype=np.float32) * 5
    panel_colors[:, 0] *= np.array([1, 0.1, 0.05, 0.025, 0.01], dtype=np.float32)
    rt.set_data(
        "panels", 
        geom=Geometry.ParallelepipedsConstSize,
        pos=np.array(pos, dtype=np.float32) + np.array([spacing, spacing, box_size + 0.1], dtype=np.float32),
        u=[panel_size, 0, 0], v=[0, panel_size, 0], w=[0, 0, 0.02],
        c=panel_colors,
        mat="glass"
        )

    rt.set_data(
        "plot", 
        geom=Geometry.ParallelepipedsConstSize, 
        pos=np.array(pos, dtype=np.float32), 
        r=box_size, 
        c=0.75
        )
    rt.set_ambient(0.9)

    x_camera = ((len(alphas) + 1) * (box_size + spacing)) / 2
    rt.setup_camera(
        name="camera1", 
        eye=[x_camera, box_size / 2, 10.0], 
        target=[x_camera, box_size / 2, 0], 
        fov=20
        )

    rt.start()

if __name__ == "__main__":
    main()

I'll post when have some progress.

[LandonRieger]

Great, thanks @robertsulej, your glass example looks as I would expect. This gives me some things to try in the meantime as well.

[robertsulej]

If refractive objects are doing good, then I can suggest the environment map, best hdr one, when the ambient light is not enough. All spherical/rect ligths are implemented as well, though tracing occlusion is even more difficult in this case. So env map should works best, and might be complemented with added geometry lights if some special effect is desired.