[HN Gopher] The white furnace test
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       The white furnace test
        
       Author : MaximilianEmel
       Score  : 215 points
       Date   : 2023-10-22 05:28 UTC (1 days ago)
        
 (HTM) web link (lousodrome.net)
 (TXT) w3m dump (lousodrome.net)
        
       | Uriopass wrote:
       | I recently implemented a PBR renderer by following the
       | learnopengl PBR tutorial.
       | 
       | It doesn't pass the white furnace test.
       | 
       | That made me realize I didn't understand much of the math I
       | implemented. Random multiplications by pi and 2 as the author
       | stated didn't work out.
        
         | CyberDildonics wrote:
         | Most BRDFs that I have seen get darker as they get rougher like
         | the article mentions. There are some that take into account the
         | interreflections of the theoretical facets that make the
         | distribution of normals that become the BRDF (mentioned in the
         | link also), and they do better but I'm not sure even they pass
         | this test straight up.
         | 
         | Most of what is actually being used out there loses energy.
         | Sometimes people have used a lookup table on top of the BRDF to
         | compensate.
        
           | pixelpoet wrote:
           | The multi scattering BRDF/BSDFs do pass the furnace tests, as
           | well as the newer hair BSDFs. I checked :)
        
       | sokoloff wrote:
       | Why "furnace" in the name of the test? I get the overall concept,
       | but the name seems fairly arbitrary. Is it, or is there an
       | anchor?
        
         | mrob wrote:
         | The inside of a hot furnace glows with the uniform illumination
         | simulated by the test.
        
         | jxf wrote:
         | The test is about being in a uniformly white-lit environment,
         | like a very hot furnace. It's just a mnemonic.
        
         | mytailorisrich wrote:
         | This is based on classic black body radiation experiments which
         | use ovens/kilns/furnace.
         | 
         | Here the concept is similar and the point is that the object is
         | enclosed in a cavity that has an uniform emission spectrum, in
         | this case white instead of black body.
        
       | pixelpoet wrote:
       | So weird to see this top of HN! Also there are actually two
       | furnace tests, the other one is with 0.5 emission and 0.5 albedo,
       | also should produce 1.0 +/- noise pixels.
       | 
       | Greetz to all path tracing people <3
        
         | yayitswei wrote:
         | I know the absolute minimum about ray tracing but could still
         | follow the article. Kudos to the author for such clear,
         | interesting writing.
        
       | Severian wrote:
       | Funny enough this Youtube video presented itself to my feed the
       | other day that goes over this very topic in the planned Blender
       | 4.0 release. They have a new Multiscatter GGX function for BSDF.
       | I think this goes a lot more in-depth and presents a lot of
       | examples.
       | 
       | https://www.youtube.com/watch?v=v6qXbV_Q7z4
        
       | raldi wrote:
       | What's the embedded ShaderToy supposed to look like? When I press
       | play and wait, nothing happens for over a minute.
       | 
       | This post would benefit greatly from a couple screenshots of
       | failed tests.
        
         | genewitch wrote:
         | it starts grey, then you see the outline of a sphere,
         | background fades in, a red, blue, and white sphere appear
         | around the central grey/white sphere, the scene fades back to
         | grey, then the red and blue sphere come back and you can see
         | the reflections or whatever on the central sphere, but you
         | can't tell it's a sphere since it's "faded in to the
         | background".
        
         | arecurrence wrote:
         | I believe it requires webgl. Can you confirm whether your
         | browser has webgl enabled?
        
           | raldi wrote:
           | Regular Chrome and Safari on a regular iPhone
        
       | distract8901 wrote:
       | Back in my day, a teapot in orbit around the sun was the best we
       | had and we _liked it_
        
       | boulos wrote:
       | Long ago, in
       | https://graphics.stanford.edu/~boulos/papers/brdftog.pdf we tried
       | to trade off energy conservation and data reproduction at the
       | cost of reciprocity.
       | 
       | In the end, nobody actually cared about automatically fitting
       | material data from BRDFs or if they do, they actually prefer a
       | symmetric and conserving-enough BSDF, which is what most future
       | research improved. In particular, breaking symmetry means making
       | bidirectional path tracing and other techniques kinda weird.
        
         | pixelpoet wrote:
         | Hey look, it's Bouliiii from the ompf forums (RIP) :D Greetz,
         | you might remember me as lycium :)
        
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       (page generated 2023-10-23 09:01 UTC)