Proof-of-Concept: Improved Transmission

[WestLangley]

Related issue: #25819

Transmission, as implemented in three.js, requires either opaque scene objects, a skybox, or an opaque scene background to serve as a source of light.

Light is transmitted and attenuated from behind the model towards the camera. If there is no light, there is no color.

Consequently, the rendering will be incorrect if the background is transparent. It will also be incorrect even if there is a CSS background, since the CSS background is not accessible to the renderer.

One workaround is to enure an opaque background is present during the transmission calculation.

There are trade-offs involved. This PR is a proof of concept for discussion.

Before:

After:

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

Filesize dev	Filesize PR	Diff
634 kB (157.2 kB)	634.1 kB (157.2 kB)	+124 B

🌳 Bundle size after tree-shaking

Minimal build including a renderer, camera, empty scene, and dependencies.

Filesize dev	Filesize PR	Diff
425.2 kB (103.1 kB)	425.3 kB (103.1 kB)	+158 B

[WestLangley]

If it is important to be able to see the CSS through the transmissive object, I can modify this proof-of-concept.

After 2:

[mrdoob]

/ping @elalish

[elalish]

@WestLangley Yes, I'd love to see how you achieved the transparent object transmitting the background. Can you update the PR here so we can see that version and test it? The current one does not seem to transmit the background through at all.

[elalish]

Thanks, this is great. What I notice as the primary differences between this and #25819 is that this PR properly reduces to the thin transmission model when thickness -> 0, retaining the specular highlights, which #25819 does not. Conversely, in #25819 as attenuationDistance -> 0, the model becomes correctly fully opaque, while this PR it transmits just as much of the background. However, I think the two approaches may yet be compatible, so I'm going to see if I can manage something that's the best of both worlds in #25819.

[WestLangley]

Closed, and replaced by a mergeable PR.