As in the title, I have an effect prepped for my game which applies certain derived parameters to a post-processing effect after the player enters a boundary I created with ProBuilder. Finding how far inside the bound the player is; that is, how far the player would have to travel, at minimum, to leave it; would help me scale this effect. It is not an axis-aligned boundary, and its sloped shape is fairly important. Having the effect go full-on on crossing the boundary would be jarring to the player.
I'm tempted to resort to traditional edge testing with this, but I would like to highlight that it will be done at least once per frame on multiple objects, so I would like to keep it as simple, and non-home-rolled, as possible.
The other possibility would be to keep track of time exposed and scale it by that; but this isn't ideal and I'm seriously curious as to whether a penetration-depth-testing method exists out-of-box.
A requested image of my setup: It is laterally symmetric, and that is unlikely to ever need to change. However, future volumes are likely to have varying angles and heights. Depth is more-or-less irrelevant, as while I'm using 3D, this game has the physics of a 2D platformer; so you can consider it to have infinite depth if you need to. As you can see on the right, I've added almost nothing to it, other than the MagneticField.cs custom script (which does not even reference the mesh, only whether it's been crossed) and a debug class, TriangleReport.cs, that I'm working on right now.
One thought I had was to get triangles for the top, bottom, left, and right edges, use them to define planes, and then determine the distance from those planes; but if you've got something better I am all ears!