[some progress] Sampling depth texture from custom camera

I managed to create a function that takes in _CameraDepthTexture from main camera and converts it into point coordinate in object space.

I also managed to sample the depth texture from a custom camera, but i have no idea how to determine the second parameter from tex2Dproj(), since it is a float4 type and i haven't found any useful description other than some vague info in Nvidia docs (they say that x and y are divied by w, but what ARE they ?).
I need to do the same thing but for custom camera.

My goal is to provide depth information to my shader from a custom camera that writes into a depth texture.

Scene is setup with a unity stock cube using my custom shader and custom camera is set with :
- culling mask that ignores only the cube, so anything passing through the volume of the cube has its depth sampled
- set to orthographic projection mode
- renders depth texture into a 512x512 depth texture (used by shader)
- it and cube are always aligned in relation to each other
- it is always in center on cube's side
- orthographicSize, nearClipPlane and farClipPlane are set to exactly match the cube size, essentially the whole "scene" frustum is covering the volume of cube

Main camera freely moves/rotates, the cube/camera combo is inside empty game object and is arbitrarily positioned/rotated like any other object in scene.

There is more going on, but this is the gist of it.

Any ideas ?

@bgolus (you must be receiving a ton of pings ...)

Setup of fbx model and a cube drawn with with custom shader



Setup of camera frustum enclosing the cube and model

 

Update : i got it to work at basic level. through a lucky accident i got correct x and y coordinates and the final z coord i got by using SAMPLE_DEPTH_TEXTURE that needs only a tex and a float2 uv inputs. The linearizing needed more work. The builtin Linear01Depth() uses near and far clipping plane from main camera so i looked how is function implemented and wrote a version that uses custom camera clipping planes floats. The depth tex and near/far floats are set through script. Once i'm done (i hope not too far in future) i'll post a link to finished code so others may figure out their own ideas.
Source used for custom depth linearize at
https://forum.unity.com/threads/_zbufferparams-values.39332/