update assignment sheet

assignments_2021/assignment1_path_tracing/assignment1_path_tracing.tex

@@ -13,11 +13,11 @@
 \deadline{2021-04-18 23:59}%2020-05-13 23:59
 \teaser{
 \hspace*{\fill}
-\includegraphics[trim={1cm 1cm 1cm 1cm},clip,width=0.32\linewidth]{figures/ref_cbox_ao_uniform.png}
+\includegraphics[trim={1cm 1cm 1cm 1cm},clip,width=0.32\linewidth]{figures/cbox_ao_uniform.png}
 \hfill
-\includegraphics[trim={1cm 1cm 1cm 1cm},clip,width=0.32\linewidth]{figures/ref_cbox_direct_mesh_surface.png}
+\includegraphics[trim={1cm 1cm 1cm 1cm},clip,width=0.32\linewidth]{figures/cbox_direct_mesh_surface.png}
 \hfill
-\includegraphics[trim={1cm 1cm 1cm 1cm},clip,width=0.32\linewidth]{figures/ref_cbox_path_tracer_parallelogram.png}
+\includegraphics[trim={1cm 1cm 1cm 1cm},clip,width=0.32\linewidth]{figures/cbox_path_tracer_mesh.png}
 \hspace*{\fill}
 \label{fig:figintro}
 }
@@ -116,7 +116,7 @@ You can also use our provided unit tests locally (maybe you have to edit the pyt
 You should base your code on \texttt{integrator\_ao.cpp} and implement it in \\
 \texttt{integrator\_direct\_lighting.cpp}.
 
-\paragraph*{Task 1} Implement the emitter interface (make either a \texttt{parallelogram\_emitter} or \texttt{mesh\_emitter}) and the supporting machinery.
+\paragraph*{Task 1} Implement the emitter interface (create either a \texttt{parallelogram\_emitter} or \texttt{mesh\_emitter}) and the supporting machinery.
 Emitters need to read their brightness (radiance) and colour from the scene file and store it (this is the least).
 A name and debug info might also be good.
 If you don't plan to implement the direct sampling, you can use a dummy implementation for Emitter::pdf() and Emitter::sample().
@@ -130,8 +130,8 @@ If you hit a regular surface instead, make a random ray cast using uniform hemis
 If the closest intersected object is a light, compute its contribution using the equations from the lecture, otherwise return zero (black).
 This is only a small edit from the \texttt{ao} integrator.
 
-\subsection{Direct light sampling (6 points)}
-Direct light sampling, is also important for performant path tracers (it's called "next event estimation" there).
+\subsection{Light surface sampling (6 points)}
+Light surface sampling is important for performant path tracers (it's called "next event estimation" or "direct light sampling" there).
 
 You will need to sample area lights directly, i.e., you need a function to randomly pick points on the surface of the light.
 There are 2 options here:
@@ -184,41 +184,17 @@ Create a new integrator and call it \texttt{path\_tracer\_recursive}(\texttt{.cp
 Start with a copy of the direct lighting integrator.
 It might pay off to keep your code clean and make small refactorings while working on it.
 
-\paragraph*{Task 1, starter code (5 easy points)}
+\paragraph*{Task 1, Start (5 easy points)}
+Use the pseudo code from the path tracing lecture slides.
 Create an additional \texttt{Li} function, that also keeps track of the current depth.
-Now you can use the pseudo code from the lecture as a template to implement a simple path tracer.
-\begin{verbatim}
-Li(Scene scene, Ray ray, int depth) {
-Color value = 0;
-
-if (!findIntersection(scene, ray))
-return value;
-
-Intersection its = getIntersection(scene, ray);
-
-// Take care of emittance
-if (isLightSource(its))
-value += getLightRadiance(its);
-
-if(depth >= 3)
-return value;
-
-// Generally, the BRDF should decide on the next ray (e.g. for specular
-// reflections). For now you can assume white diffuse BRDF and uniform
-// hemisphere sampling. Therefore, replace the code as you see fit.
-BRDF brdf = getBRDF(its);
-Color brdfValue = sampleBrdf(brdf, -ray, wo);
-
-// Call recursively for indirect lighting
-value += brdfValue * Li(scene, wo, depth + 1);
-return value;
-}
-\end{verbatim}
+For the first task, you only have to implement a fixed depth recursion.
+You can choose to use a constant in code, or a parameter, but the default must be a depth of 3.
 
 And you can observe how the image becomes more realistic as you increase the depth.
 
 \paragraph*{Task 2, Russian Roulette (1 easy and 2 normal points)}
 Implement Russian Roulette with a minimum depth of 4 according to the slides.
+This must be parametrised from the scene file.
 It's probably easier to implement first a version with fixed probabilities (1 Point).
 
 But the proper way to do it is to keep track of the \textit{throughput}.