You're reading from Mastering Graphics Programming with Vulkan

Product type Book

Published in Feb 2023

Publisher Packt

ISBN-13 9781803244792

Pages 382 pages

Edition 1st Edition

Languages

Concepts

Game Optimization

Authors (2):

Marco Castorina

Gabriel Sassone

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Table of Contents (21) Chapters

Preface

1. Part 1: Foundations of a Modern Rendering Engine

2. Chapter 1: Introducing the Raptor Engine and Hydra

3. Chapter 2: Improving Resources Management

4. Chapter 3: Unlocking Multi-Threading

5. Chapter 4: Implementing a Frame Graph

6. Chapter 5: Unlocking Async Compute

7. Part 2: GPU-Driven Rendering

8. Chapter 6: GPU-Driven Rendering

9. Chapter 7: Rendering Many Lights with Clustered Deferred Rendering

10. Chapter 8: Adding Shadows Using Mesh Shaders

11. Chapter 9: Implementing Variable Rate Shading

12. Chapter 10: Adding Volumetric Fog

13. Part 3: Advanced Rendering Techniques

14. Chapter 11: Temporal Anti-Aliasing

15. Chapter 12: Getting Started with Ray Tracing

16. Chapter 13: Revisiting Shadows with Ray Tracing

17. Chapter 14: Adding Dynamic Diffuse Global Illumination with Ray Tracing

18. Chapter 15: Adding Reflections with Ray Tracing

19. Index

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Adding Volumetric Fog

After adding variable rate shading in the previous chapter, we will implement another modern technique that will enhance the visuals of the Raptor Engine: Volumetric Fog. Volumetric rendering and fog are very old topics in rendering literature, but until a few years ago, they were considered impossible for real-time usage.

The possibility of making this technique feasible in real-time stems from the observation that fog is a low-frequency effect; thus the rendering can be at a much lower resolution than the screen, increasing the performance in real-time usage.

Also, the introduction of compute shaders, and thus generic GPU programming, paired with clever observations about approximations and optimizations of the volumetric aspect of the technique, paved the way to unlocking real-time Volumetric Fog.

The main idea comes from the seminal paper by Bart Wronski (https://bartwronski.files.wordpress.com/2014/08/bwronski_volumetric_fog_siggraph2014.pdf) at...

Technical requirements

The code for this chapter can be found at the following URL: https://github.com/PacktPublishing/Mastering-Graphics-Programming-with-Vulkan/tree/main/source/chapter10.

Introducing Volumetric Fog Rendering

What exactly is Volumetric Fog Rendering? As the name suggests, it is the combination of Volumetric Rendering and the fog phenomena. We will now give some background on those components and see how they are combined in the final technique.

Let’s begin with Volumetric Rendering.

Volumetric Rendering

This rendering technique describes the visuals associated with what happens to light when it travels through a participating medium. A participating medium is a volume that contains local changes to density or albedo.

The following diagram summarizes what happens to photons in a participating medium:

Figure 10.2 – Light behavior in a participating medium

What we are trying to describe is how light changes when going through a participating medium, namely a fog volume (or clouds or atmospheric scattering).

There are three main phenomena that happen, as follows:

Absorption: This happens...

Implementing Volumetric Fog Rendering

We now have all the knowledge necessary to read the code needed to get this algorithm fully working. From a CPU perspective, it is just a series of compute shaders dispatches, so it is straightforward.

The core of this technique is implemented throughout various shaders, and thus on the GPU, working for almost all steps on the frustum aligned Volumetric Texture we talked about in the previous section.

Figure 10.7 shows the different algorithm steps, and we will see each one individually in the following sections.

Data injection

In the first shader, we will write scattering and extinction, starting from the color and density of different fog phenomena.

We decided to add three different fog effects, as follows:

A constant fog
Height fog
Fog in a volume

For each fog, we need to calculate scattering and extinction and accumulate them.

The following code converts color and density to scattering and extinction...

Summary

In this chapter, we introduced the Volumetric Fog rendering technique. We provided a brief mathematical background and algorithmic overview before showing the code. We also showed the different techniques available to improve banding – a vast topic that requires a careful balance of noise and temporal reprojection.

The algorithm presented is also an almost complete implementation that can be found behind many commercial games. We also talked about filtering, especially the temporal filter, which is linked to the next chapter, where we will talk about an anti-aliasing technique that uses temporal reprojection.

In the next chapter, we will see how the synergy between Temporal Anti-Aliasing and noises used to jitter the sampling in Volumetric Fog will ease out the visual bandings. We will also show a feasible way to generate custom textures with a single-use compute shader used to generate a volumetric noise.

This technique is also used for other volumetric algorithms...