How to create a partial transparent wall?

Question

I try to build a See-Through system in godot v3.1.1.
The wall will partial transparency while the player has been covered.

I change texture when the character has cover by area trigger, but when I toggle transparent flag, the shadow disappears!
How can I fix them?
Are there other ways to transparent partial of wall?
Something like unity see-through-system?

Comments

Have you tried playing around with the alpha channel of the wall? If it's a Sprite, you may be able to make it partially transparent.

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I wonder if it's possible for transparent objects to cast full shadows Oo
If not, maybe you could leave it opaque, but add a shader to it with dithering. So it would not be half-transparent, but you will be able to hide pixels per pixels, a bit like the one that can be seen in the official TPS demo (but that one is distance fade+``PixelDither`, not what you want but shows the effect). However I don't know if that's gonna affect shadows... you should give it a try.

I also thought you could check Opaque Pre-pass. Unfortunately, it also modifies the shadow, i.e the transparent parts are also removed from the shadow :(