sample_loader_app

Scene loader

This sample demonstrates loading scene from HydraXML format and rendering it with simple ray tracing renderer. The renderer traces only primary rays and computes color by sampling predefined color palette with mesh/instance id. The renderer uses embree, which is precompiled and included in this repository for your convenience.

Building

All dependencies are included in this repo. Binary will be built in the same directory as this README file.

Use CMake as usual to build the sample application. For example, on Linux from this directory execute:

mkdir build
cd build
cmake ..
make

On Windows you would usually just open this directory as a CMake project in Visual studio or other IDE supporting CMake.

Loader description and usage

HydraXML format

Overall, scene in HydraXML format consists of XML-description file and binary geometry/texture files, usually located in "data" directory alongside the XML file. It is similar to glTF format, however, currently there is no predefined structure to various scene objects, so you need to interpret XML attributes and values by yourself.
XML file contains several so-called libraries:

• textures_lib - texture description (resolution, etc.) often referencing to an image file;
• materials_lib - material model description (diffuse component, reflection component, etc.), possibly with references to textures_lib;
• geometry_lib - mesh description (byte size, vertices number, primitives number, vertex attributes etc.) referencing a geometry file in internal .vsgf format (loader for these files is located here);
• lights_lib - light model description (shape, size, distribution, etc.), possibly with reference to IES file;
• cam_lib - camera model description (fov, clip planes, position, etc.)
• render_lib - render setting description (resolution, algorithm, etc.), usually for a specific renderer (most often Hydra renderer)
• scenes - scene description (mesh instances referencing geometry_lib, light instances referencing lights_lib, etc.)

Details on HydraXML format can be found here.

Loader

Loader uses pugixml to parse HydraXML format. Loader interface is located in hydraxml.h.

Simple scene loading example is provided by this sample application - check RayTracer::LoadScene function here.

More complete example can be found in vk_graphics_rt repo.

Now, let's take a look at scene loading process step by step.

Basic usage is to create HydraScene object, load XML scene description file and iterate over objects in each library (described above - geometry_lib, materials_lib, etc.) you need:

hydra_xml::HydraScene scene;
scene.LoadState("../01_simple_scenes/instanced_objects.xml");

MeshFiles() and TextureFiles() let you iterate over file paths with range based for:

for(auto meshPath : scene.MeshFiles())
{
  auto currMesh = cmesh::LoadMeshFromVSGF(meshPath.c_str());
  // store/use loaded mesh data
  // ... 
}

TextureNodes(), MaterialNodes(), GeomNodes(), LightNodes() and CameraNodes() let you iterate over XML nodes with range based for. You will need to get desired XML attributes and values by their name (or iterate over them using pugixml methods)

for(auto materialNode : scene.MaterialNodes())
{
  auto node = materialNode.child(L"diffuse").child(L"color");
  if(node != nullptr)
    color = LiteMath::to_float4(hydra_xml::readval3f(node), 0.0f);

  // load other components if needed
  // check for texture references, etc.
  // ...
}

Cameras() and lets you iterate over hydra_xml::Camera structs with range based for (camera description is loaded from XML into hydra_xml::Camera struct in hydra_xml::CamIterator class). You can also load camera model from XML by yourself by using CameraNodes() method.

MaterialsGLTF() analogously lets you iterate over hydra_xml::gltfMaterialData structs by converting Hydra Renderer material into approximate glTF PBRMetallicRoughness material.

for(auto cam : scene.Cameras())
{
  float aspect   = 1.0f;
  auto worldView = LiteMath::lookAt(LiteMath::float3(cam.pos), LiteMath::float3(cam.lookAt), LiteMath::float3(cam.up));
}

Finally, after loading all desired assets from libraries, you will usually iterate over instances in the scene using InstancesGeom() method to get hydra_xml::Instance structs, containing mesh id, matrix and remap list id (remap lists allow you to change materials assigned to mesh on per instance basis, check HydraXML docs for more information).

for(auto inst : scene.InstancesGeom())
{
  m_pAccelStruct->AddInstance(inst.geomId, inst.matrix);
}