Headerless examples - Githubissues

Hello,

This is a new PR, which should be applied after the Layout Menu PR.

It simplifies the registration of examples via:

An example can now work :

without a header file
without the need to register it manually inside a separate index file (such as for example /_loaders_gltf_samples_index.cpp): the macro BABYLON_REGISTER_SAMPLE simplifies the registration

See for example two commits where I did this

For animation101 scene
For TwoCylinderEngineScene

Explanations:

BABYLON_REGISTER_SAMPLE(_LoadersGLTFSamplesIndex::CategoryName(), TwoCylinderEngineScene)

will automatically register the example (and make the example name equal to the class name)

BABYLON_REGISTER_SAMPLE is a macro with some black magic inside, but I tried to explain it clearly:

// BABYLON_REGISTER_SAMPLE : registers an example in the Samples Index
// No need to create a header file, and no need to add it manually to the index
//
// This macro uses 3 black magic elements:
// 1. macro "token pasting" in order to create structure name per sample
// 2. A Raii structure that will register the sample on creation
// 3. a global variable of the Raii structure in order to do the actual registration
#define  BABYLON_REGISTER_SAMPLE(categoryName, sampleClassName)                                    \
  struct RaiiRegisterer_##sampleClassName {   /* 1. This struct name depends on the sample name */ \
    RaiiRegisterer_##sampleClassName()        /* 2. inside its constructor, it triggers         */ \
    {                                         /* the registration                            */    \
       BABYLON::Samples::SamplesIndex::Instance().RegisterSample(categoryName, #sampleClassName,   \
                     [](ICanvas* iCanvas) { return std::make_unique<sampleClassName>(iCanvas); }); \
    }                                                                                              \
  };                                                                                               \
  RaiiRegisterer_##sampleClassName gRaiiRegisterer_##sampleClassName; /* 3. global variable */

samdauwe / BabylonCpp

Headerless examples #49