A real cloud consists of many-many water particles spread out at random. Each particle is tiny and spread out at random with (typically) a lot of empty space between particles. A real light ray is scattered all over the cloud in variety of directions. It would incredibly difficult and computationally intensive to replicate reality-based ray tracing algorithm.
Our simplified approach was to shoot a ray towards the light source from our original ray as it passes through the cloud and sample densities from that point towards the light source. Then we continue marching though our clouds repeating the process. This is done for every ray shot through our cloud.
The most difficult part of ray marching the cloud is correctly mixing the “marched densities” with color for final output. In order to pick the correct mixing parameters, we added three additional setting to our GUI. This enabled us to play with ray marching settings on the fly.
After a lot of tinkering with values and textures, we were finally able to get realistic looking clouds that resemble our goal (left image). Lastly we added a gradient background to the rest of the scene (right image).
