BxDF tests

[Przemog1]

No description provided.

[devshgraphicsprogramming]

why do you have random things from sorakrit here instead of your own branch against his or master ?

I literally can't see whats yours and what's @keptsecret's.

[devshgraphicsprogramming]

the third random number is sometimes necessary to discern discrete BxDF branches:

• reflection vs refraction in e.g. glass
• diffuse vs specular in e.g. plastic
• choosing a leaf BxDF in a mixture/tree of BxDFs

[devshgraphicsprogramming]

your new code is still testing with u.z=0

while the jacobian test can't work with varying u.z, its important to test varying u.xy for different constant values of u.z

I'm pretty sure the Chi2 and bucket/histogram tests can handle varying u.z (and you should vary it)

[devshgraphicsprogramming]

returning a result as a vec4 is quite a bit meh, I'd actually provide a callback (via static polymorphism) which is only called upon a failure

struct FailureCallbackConceptExample
{
   void __call(NBL_CONST_REF_ARG(SBxDFTestResources) failedFor, NBL_CONST_REF_ARG(sample_t) failedAt);
};

then you can print in C++, mark booleans, append to vector, break & repeat call or whatever

[devshgraphicsprogramming]

perfect C++ callback

printf(...your error message...);
for (volatile bool repeat=true; gDebuggerAttached&&repeat; )
{
   repeat = false; // I can set to true with debugger and repeat as many times as I want till I find the cause
   __debugbreak();
   failedFor.test(failedAt);
}

[devshgraphicsprogramming]

setting those thousands of times will be expensive, function should be void and not return anything, callback instead of meta

[devshgraphicsprogramming]

I'd make the function take uint32_t as an argument, then run a hash function (wide not deep)
https://rene.ruhr/gfx/gpuhash/

This will make it easy to invoke multiple run(uint32_t invocationID) in parallel independently, be it on CPU with for loop or GPU with gl_GlobalInvocationID.x

[devshgraphicsprogramming]

there's no point to this test existing, the test I've outlined ONLY makes sense for varying (differentiating) the 2D random number xi, because thats the uniform distribution that must be stretched and squeezed to form the PDF of the importance sampler

[devshgraphicsprogramming]

use a nice callback

[devshgraphicsprogramming]

you need to run the tests thousands of times with different seeds, I'd use for_each over a ranges::iota_view with par_unseq policy to perform these tests on all CPU cores at once.
https://godbolt.org/z/xvxE7jzE3

this connects with https://github.com/Devsh-Graphics-Programming/Nabla-Examples-and-Tests/pull/165/files#r1906914911

[devshgraphicsprogramming]

h should be a parameter of each individual specialized BxDF test, because its specific to the differential test and also may need to change depending on the BxDF getting tested

[devshgraphicsprogramming]

also maybe compute the perturbed u above for readability

[devshgraphicsprogramming]

this needs to be done better semantically with a callback, one thing for each individually.

Alos pdf.value() does not equal brdf in general!!!!!

P.s. the *0.5 thing on the PDF to Jacobian ratio was a thing for visualization, you should really have a callback which gets triggered if the value is too far from 1.0

[devshgraphicsprogramming]

you need to skip checking anything that produces an "impossible" s, so if eval or quotient is 0, you can skip the rest of the function (but not before you check pdf and quotient for 0 and INF respectively - the checks also check for NaN)

add more simple tests for:

1. pdf>0 because something you generated cannot have 0 probability of getting generated
2. quotient<INF always because our importance sampler's job is to prevent that!
3. positivity, all pdf, quotient, and eval need to be >=0
4. recprocity (eval must be equal if we swap L and V around, make a method/function to swap L and V around in s, the interaction, the bxdf itself and the cache)

Leave lots of comments.

[devshgraphicsprogramming]

Also when pdf is close to INF (above some super high threshold) you need to back off the last test you have here

[devshgraphicsprogramming]

not projected hemisphere, just hemisphere.

Also not hemisphere but full sphere, because its good to test that BRDFs handle invalid (below hemisphere) correctly

[devshgraphicsprogramming]

#165 (comment)

[devshgraphicsprogramming]

do a quick quaternion.hlsl we can refine later (create from matrix<T,3,3> and createAngleAxis)

have it store vector<T,4> data member

its important that GPU also does the test with rotated tangent frames

[keptsecret]

I've changed it to use the rotation_mat in math/linalg/transform.hlsl instead. Do we still want this quaternion.hlsl?

[devshgraphicsprogramming]

what is state ?

[keptsecret]

It's the loop iteration number. Pass into pcg to get uint32_t2 seed for xoroshiro rng. Same as here as well
#165 (comment)