disable sortForAlpha makes objects opaque

[JirkaDellOro]

Introduced with

Date: Mon Jul 08 2024 15:22:45 GMT+0200 (Central European Summer Time)
disable blending for opaque objects

Is this the desired behaviour? sortForAlpha now means more than what it says...

[plojo]

This is the intended behaviour for now.
I made this change to support glTF Alpha Coverage alphaMode: MASK ("The rendered output is either fully opaque or fully transparent depending on the alpha value and the specified alpha cutoff value". I also added an alphaClip (alpha cutoff value) property to the Material.
With the current sortForAlpha and alphaClip we can support all glTF alphaModes:

• OPAQUE: sortForAlpha: false; alphaClip: 0
• MASK: sortForAlpha: false; alphaClip: 0-1
• BLEND: sortForAlpha: true; alphaClip: 0

However i am not pleased with the current situation:

• As you stated sortForAlpha now means more than what it says. We need to find fitting names for our properties.
• alphaClip is a Material property, sortForAlpha is a ComponentMaterial property. This is confusing, both should be properties of the same class. (In both three.js aswell as Unity these options seem to purely belong to a Material)
• three.js seems to support alpha coverage the same way we do. The corresponding Material properties are named .transparent and .alphaTest. In Unity this is implemented via the RenderingMode-Dropdown. Maybe a dropdown with different options would be easier to understand?