Global Fog

Global fog is used to simulate fog effects in outdoor environments in games. In addition to fog effects in the game, it can also be used to hide the model outside the camera's far clipping plane to improve the rendering performance.

The global fog currently includes four types: Linear Fog, Exponential Fog, Exponential Squared Fog, and Layer Fog, please refer to the Global Fog Types section below for additional details.

Enable Global Fog

Check Scene in the Hierarchy panel, then check the Enabled property in the Fog component of the Inspector panel to enable global fog.

Accurate Fog Computing

Prior to v3.4, Creator used vertex fog by default, which caused unusual fog transitions on objects with a few vertices and a large volume. Starting with v3.4, Creator added the Accurate option to enable pixel fog to solve this problem.

The effect when the Accurate option is unchecked, i.e., the pixel fog is not enabled, is as follows:

The effect when the Accurate option is checked, i.e., the pixel fog is enabled, is as follows:

Version Upgrade - Effect Migration

When a project is upgraded to v3.4, all the Effect code that calls to CC_APPLY_FOG needs to be modified to add a second parameter, worldPos. e.g.:

• The original code is as follows:

  CC_APPLY_FOG(finalColor);

• After upgrading to v3.4, the original code needs to be changed to the following:

  CC_APPLY_FOG(finalColor, v_position.xyz);

Types of Global Fog

The types of global fog include Linear Fog, Exponential Fog, Exponential Squared Fog, and Layer Fog. The type depends on the calculation result of Camera and Model Vertex, which is called Fog Blend Factor. The fog blend factor determines how the fog color and the model color are blended, resulting in a different global fog effect.

Linear Fog

Property	Description
Enabled	Whether to enable the global fog.
Accurate	Whether to enable accurate fog computing.
FogColor	The color of the global fog.
Type	The type of the global fog.
FogStart	The starting position of the fog effect.
FogEnd	The end position of the fog effect.

The fog blend factor of Linear Fog is calculated by the formula:

f = (FogEnd - Cam_dis) / (FogEnd - FogStart)

• When Cam_dis = FogEnd, i.e., the distance between the camera and the model vertex is equal to FogEnd, the blend factor is calculated as 0, and the object is fully fogged.

• When Cam_dis = FogStart, i.e. the distance between the camera and the model vertex is equal to FogStart, the blend factor is calculated as 1, and the object is not affected by fogging.

To increase the density of Linear Fog when the distance between the camera and the model vertex is fixed, there are two ways:

1. Fix the value of FogStart and decrease the value of FogEnd.
2. Decrease the value of FogStart and fix the value of FogEnd.

To adjust the fog effect to the right consistency, it is best to adjust both the FogStart and FogEnd properties appropriately.

Exponential Fog and Exponential Squared Fog

The properties of Exponential Fog and Exponential Squared Fog are the same, and the Exponential Fog is used here as an example:

Property	Description
Enabled	Whether to enable the global fog.
Accurate	Whether to enable accurate fog computing.
FogColor	The color of the global fog.
Type	The type of the global fog.
FogDensity	The fog density, the value range is 0 ~ 1, the larger the value the higher the density.
FogStart	The starting position of the fog effect.
FogAtten	Fog attenuation coefficient, the smaller the value the denser the fog.

The fog blend factor for Exponential Fog is calculated as:

f = e^(-max(0, distance-fogStart) * fogDensity)

The fog blend factor for Exponential Squared Fog is calculated as:

f = e^(-max(0, distance-fogStart) * fogDensity)²

Developers can adjust the distribution of global fog in the near and far distance with FogStart, and the fog concentration at different locations with FogDensity and FogAtten.

Layered Fog

Layered Fog is parallel to the horizontal plane and has a specific height. The height of the fog can be determined by setting the top of the Layered Fog at any position in the vertical direction of the scene world coordinate system.

Property	Description
Enabled	Whether to enable the global fog.
Accurate	Whether to enable accurate fog computing.
FogColor	The color of the global fog.
Type	The fog type of the global fog.
FogAtten	Fog attenuation coefficient, the smaller the value the denser the fog.
FogTop	The position of the model vertices in the vertical direction of the world coordinate system, below which all vertices will be affected by the fog effect.
FogRange	The range of the fog effect from the set FogTop downwards.

The fog calculation of Layered Fog is a bit more complicated than the other three fog types, as it introduces the concept of FogTop and also requires distance calculation in the X-Z plane.

Layered Fog is more common in reality, with towering mountains and buildings. If it is used wisely, it is believed to have a good effect on scene presentation, but at the same time, the computation will be increased, developers can decide according to their needs.