Why do small objects not cast shadows?

[francisdb]

I'm rendering a pinball table with small meshes. Eg the ball is 27mm

Starting with https://bevyengine.org/examples/3d-rendering/3d-scene/ and reducing the size of the cube until it's that small will cause it to lose it's shadow. Below examples for cubes of 0.04, 0.06, 0.08 and 0.10

Also the shadow looks rather low-res at this scale. Sphere with radius 0.05 shown here.

And a movie that shows the issue, shadows disappear before the objects hit the floor.

Screencast.From.2025-04-04.14-45-00.webm

Should I somehow indicate I would like to have the shadows working on a smaller scale?

[jf908]

Try playing around with the shadow settings, there's some on the PointLight component and there's the PointLightShadowMap resource.

I assume when the object is too small, it becomes smaller than 1 pixel from the point light's POV so increasing the point light shadow map resolution's from the 1024 default with:

app.insert_resource(PointLightShadowMap {
    size: 2048,
});

will fix the problem but will increase rendering cost.

The settings are intended to make sense with a "standard" scene size but its intentional that you'll have to tweak things with small or big scenes.

[francisdb]

Thanks. The PointLightShadowMap makes the shadows a bit sharper but it did not fix them disappearing.

[francisdb]

Somewhat answering my own question after some research:

• Setting PointLight shadow_depth_bias: 0.01 or lower fixed the disappearing part. I'm not sure why and if that comes with other implications.
• Bringing the light closer to the objects will make the shadows crisper (and harder).

Other things I tried

Increasing the PointLightShadowMap makes the shadows a bit sharper but this might be expensive.

The camera ShadowFilteringMethod Gaussian or Temporal improves the look of the shadow.

I tried playing with the CascadeShadowConfigBuilder values but did not see any difference, probably because the distance from the light to the objects is not varying that much.