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I've searched many posts going back to Processing 1 and have found this issue documented but no resolution or workaround.
The proposed "solution" to enabling alpha transparency in 3D is to use
hint(DISABLE_DEPTH_TEST). However, as well documented, this destroys the Z order causing lines/objects to be rendered on top of each other incorrectly, and where an object should pass "behind" another and be obscured by it, the geometry/perspective correctly places it back there, but the visual rendering shows the far objects drawn on top of the near ones. It's like viewing layers in reverse order. In addition, it would seem that transparency is either on or off, i.e., to have an object be transparent the object seen through it is at full saturation, with no toning by different alpha values of the translucent panel in front of it. This would make sense in that it is not really showing transparency, rather rear objects are drawn on top, and therefore the object can be "seen" through the alpha fill.
Does anyone have a solution for this issue? Just disabling the depth test messes up the rest of the 3D rendering, so it's either drop any form of alpha transparency in 3D or have the scene rendered incorrectly. FWIW, I've also tried
hint(ENABLE_DEPTH_SORT) plus their inverses (DISABLE...) to no avail/difference.
Thanks in advance for any insight into this