Better documentation and added one for visibility function

apps/tutorials/pe/02_ConfinedGasExtended.cpp

@@ -171,7 +171,7 @@ int main( int argc, char ** argv )
    
    WALBERLA_LOG_INFO_ON_ROOT("*** RAYTRACER ***");
    //! [Raytracer Init]
-   std::function<ShadingParameters(const BodyID body)> customShadingFunction = [](const BodyID body) {
+   std::function<ShadingParameters (const BodyID body)> customShadingFunction = [](const BodyID body) {
       if (body->getTypeID() == Sphere::getStaticTypeID()) {
          return processRankDependentShadingParams(body).makeGlossy();
       }

apps/tutorials/pe/02_ConfinedGasExtended.dox

@@ -93,31 +93,48 @@ functions so you do not have to extract all the information yourself and save it
 \snippet 02_ConfinedGasExtended.cpp SQL Save
 
 \section tutorial_pe_02_raytracing Image Output
-Using a raytracer snapshots of the simulation can be generated each timestep and output as PNG files.
-Setting up the Raytracer can be done by reading a config object, as it is done in the tutorial:
+Using the pe::raytracing::Raytracer you can generate images of the simulation for each timestep and output them as PNG files.
+Setup the raytracer by reading a config object and optionally supply a shading and a visibility function, 
+as it is done in the second pe tutorial. The shading function will be called during rendering for each body
+to apply user defined coloring to bodies, the visibility function to determine if a body should be visible or not.
 \snippet 02_ConfinedGasExtended.cpp Raytracer Init
-Alternatively it can also be entirely setup in code:
+Alternatively it may also be setup entirely in code:
 \code
 Lighting lighting(Vec3(-12, 12, 12),
                   Color(1, 1, 1),
                   Color(1, 1, 1),
                   Color(real_t(0.4), real_t(0.4), real_t(0.4)));
 Raytracer raytracer(forest, storageID, globalBodyStorage, ccdID,
-                  640, 480,
-                  real_t(49.13), 2,
-                  Vec3(-25, 10, 10), Vec3(-5, 10, 10), Vec3(0, 0, 1),
-                  lighting,
-                  Color(real_t(0.1), real_t(0.1), real_t(0.1)),
-                  radius,
-                  customShadingFunction);
+                    640, 480,
+                    real_t(49.13), 2,
+                    Vec3(-25, 10, 10), Vec3(-5, 10, 10), Vec3(0, 0, 1),
+                    lighting,
+                    Color(real_t(0.1), real_t(0.1), real_t(0.1)),
+                    radius,
+                    customShadingFunction;
 \endcode
-To apply custom coloring to bodies, you can supply a user defined function which returns a ShadingParameters struct for
-a given BodyID. For an overview over predefined shading functions, visit the file ShadingFunctions.h.
 After the configuration is done, images can be generated each timestep by calling Raytracer::generateImage<BodyTuple>()
 which will be output to the specified directory.
 \snippet 02_ConfinedGasExtended.cpp Image Output
-For further information see the documentation for the classes Raytracer and Lighting, the ShadingParameters class and
-ShadingFunctions.h file may also be useful.
+To hide certain bodies during rendering, the visibility function will be called with a BodyID as its sole argument 
+and should return true if the object is supposed to be visible, false if not:
+\code
+// [...]
+std::function<bool (const BodyID body)> customVisibilityFunction = [](const BodyID body) {
+  if (body->getTypeID() == Plane::getStaticTypeID()) {
+     // hide all planes
+     return false;
+  }
+  return true;
+};
+Raytracer raytracer(forest, storageID, globalBodyStorage, ccdID,
+                   cfg->getBlock("Raytracing"),
+                   customShadingFunction,
+                   customVisibilityFunction);
+\endcode
+For an overview over predefined shading functions, visit the file ShadingFunctions.h.
+For further information see the documentation for the classes pe::raytracing::Raytracer, pe::raytracing::Lighting and 
+pe::raytracing::Color, the pe::raytracing::ShadingParameters struct and ShadingFunctions.h file may also be useful.
 
 */