Debug Japanese Classroom scene

[wahn]

The C++ version does render the Japanese Classroom scene (from https://benedikt-bitterli.me/resources) fine:

Whereas the current Rust version panics:

> ./target/release/examples/pest_test -i ../../../../Downloads/classroom/scene.pbrt
FILE = ../../../../Downloads/classroom/scene.pbrt
search_directory is /home/jan/git/self_hosted/Rust/pbrt/../../../../Downloads/classroom
13596 bytes read
...
Rendering with 4 thread(s) ...
block_queue.len() = 3726
thread '<unnamed>' panicked at 'ld = RGBSpectrum { c: [-0.008398388, -0.010858062, -0.013359588] }', src/integrators/path.rs:128:29
note: Run with `RUST_BACKTRACE=1` for a backtrace.
thread '<unnamed>' panicked at 'ld = RGBSpectrum { c: [-12.454978, -12.454978, -12.454978] }', src/integrators/path.rs:128:29
1 / 3726 [>--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------] 0.03 % 43633.82/s 0s 
thread '<unnamed>' panicked at 'ld = RGBSpectrum { c: [-11.307451, -11.307451, -11.307451] }', src/integrators/path.rs:128:29
thread '<unnamed>' panicked at 'ld = RGBSpectrum { c: [-19.646214, -19.646214, -19.646214] }', src/integrators/path.rs:128:29
thread '<unnamed>' panicked at 'called `Result::unwrap()` on an `Err` value: RecvError', /checkout/src/libcore/result.rs:916:5
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: Any', /checkout/src/libcore/result.rs:916:5

[wahn]

It looks like FresnelBlend::schlick_fresnel(...) returns sometimes colors (Spectrum) with negative values.

[wahn]

After removing all SubstrateMaterial materials (and the geometry using it) we can render with the Rust version:

So the problem might be missing implementations for transformations encapsulated via TransformBegin and TransformEnd:

> rg Transform ../../../../Downloads/classroom/scene.pbrt
2:Transform [ 0.988479 -0.00428443 0.151294 -0 -0 0.999599 0.0283071 -0 0.151355 0.027981 -0.988083 -0 0.780055 -1.44302 6.03615 1]
82:	TransformBegin
83:		Transform [ 1 0 0 0 0 1 0 0 0 0 1 0 0 -0.0734223 0 1]
85:	TransformEnd
122:	TransformBegin
123:		Transform [ 11.6517 0 0 0 0 11.6517 0 0 0 0 11.6517 0 0 0 0 1]
125:	TransformEnd
201:	TransformBegin
202:		Transform [ 1 0 0 0 0 1 0 0 0 0 1 0 0 -0.0734223 0 1]
204:	TransformEnd
206:	TransformBegin
207:		Transform [ 1 0 0 0 0 1 0 0 0 0 1 0 0 -0.0734223 0 1]
209:	TransformEnd
211:	TransformBegin
212:		Transform [ 1 0 0 0 0 1 0 0 0 0 1 0 0 -0.0734223 0 1]
214:	TransformEnd
216:	TransformBegin
217:		Transform [ -1 0 8.74228e-008 0 -8.74228e-008 0 -1 0 0 1 0 0 0 0 0 1]
219:	TransformEnd

[wahn]

Since commit 05fb6c4 all problems regarding rendering the Japanese Classroom scene should be solved:

There is a difference between the C++ and Rust version though:

> imf_diff -d -f classroom.png pbrt.png 
differing pixels:	 45.988% (423830 of 921600)
average difference:	  2.608%
maximum difference:	 54.947%
Summary: Many pixels differ strongly.
== "classroom.png" and "pbrt.png" are different

Good enough to close the issue ...

[wahn]

And this is how Rust renders the scene in about 7 hours (still using uni-directional path tracing):