Now that we've caught up, we can start working on a volume renderer. Any watertight (closed, non-self-intersecting, manifold) mesh can be used to construct a volume. There are already a lot of tools that can produce a volume for us, such as the Unity build-in tool named SDF Bake Tool. However, we opted for a more programatical approach and used a library called IGL. This library is developed in C++ and may be used to produce a volume as part of our pipeline. The steps for creating a volume with the IGL library are as follows. First, we import a mesh (which is also possible using an IGL function igl::readObj). Next we feed the data that was imported into IGL's signed distance function:
When executing this function properly a volume should be created.
Generated signed distance field of the Standford Bunny - IGL.
As previously indicated, we employed a deferred rendering approach to incorporate our volumetric renderer into a conventional rendering pipeline. This means that our volumetric framebuffer will produce a G-Buffer. This G-Buffer was built by leveraging our sphere-tracer within the fragment shader of our render pass. This renderpass might be created using the following pseudocode:
Accompanied with this render pass comes a shader which traces against our generated volume.
We now have all of the data we need to develop a high-quality renderer. The data in the G-Buffer is given to the lighting pass, which calculates all relevant lighting information needed to illuminate our scene. Furthermore, the produced frame might be enhanced using other rendering techniques such as ambient occlusion, reflection, or subsurface scattering. Other material attributes, such as roughness and metallicity, might be added to the lookup table in addition to albedo and specular values. This would allow us to make a PBR material that we could use on our traced volume (We opted simple diffuse shading since light propagation and varied visual effects are not the focus of this post). Finally, to create a depth buffer, the travelled distances might be translated back to the camera's distance. The depth buffer could be used to create a hybrid approach that combines surface-based geometry with volumetric data in the same scene.