Summary
rPBR is a 3D viewer to render models using physically based rendering (PBR) pipeline. The tool is written in pure C language using raylib framework and OpenGL, using structs to support multi-material scenes, multiple lights and some useful render settings and features.

 
Highlights
– Phyiscally based rendering for any 3D model.
– Metalness/Roughness PBR workflow.
– Split-Sum Approximation for specular reflection calculations.
– Support for normal mapping, parallax mapping and emission mapping.
– Point and directional lights supported.
– Load OBJ models and texture images in real-time by drag and drop.
– Internal shader values and locations points handled automatically.

 
Downloads

  –   Click here to download rPBR for Windows.
  –   Click here to see source code.

Screenshots

Comparison with Marmoset Toolbag rendering

You can see all required shading calculations to achieve the PBR final result (albedo, normals, metalness, roughness, lighting, fresnel, irradiance (GI) and reflections: