Changing transparent property doesn't have any effect on materials, if true is not provided in the constructor

[soadzoor]

Describe the bug

It seems the since r137, the default value for transparent prop for materials need to be true (provided in the constructor) if you ever want to make the material transparent in its lifetime. If the default value is false (or is not provided), then changing it to true won't have any effect.

To Reproduce

Steps to reproduce the behavior:

1. Create a mesh
2. Some time later (with setTimeout, or by a click event, or anything), attempt to make the material transparent, like this: mesh.material.transparent = true; mesh.material.opacity = 0.5;
3. Note how the material remains unchanged

Live example

https://jsfiddle.net/9cjg5ofs/2/

Expected behavior

Prior r137, it worked as expected, users could change the transparent property from true to false, and vica versa, and it took effect immediately.

Proof of this (same code, different three.js version (r136)): https://jsfiddle.net/a7hotpb2/

Platform:

• Three.js version: [dev, r137+]

[soadzoor]

It seems the following workaround works: material.needsUpdate = true. But it's not very nice, since it was not required before r137. Also, I can't see any information about this in the migration guides, so I guess it's not the intended behavior.

[Mugen87]

see #23576 (comment)

We updated the docs with the new behavior. The change is actually noted in the migration guide for 136 → 137 (see last note).

https://github.com/mrdoob/three.js/wiki/Migration-Guide#136--137

[soadzoor]

@Mugen87 Oh, right, I must've overlooked, sorry.
But it does work the other way around, though: changing it from true to false, without settings needsUpdate = true. Is that okay?

[Mugen87]

It works because blending is disabled. However, the define OPAQUE would still be set in your shader which can produce issues. Probably not in your particular case.