Mountain Edge and Surface Transition Management

Dealing with the transition between mountain edges and the terrain surface is a challenging issue. Traditional approaches involve using objects for obstruction (such as trees) and employing techniques like edge transparency. However, these methods often lead to increased performance overhead and processing complexity. The use of transparency introduces the following issues:

1. Alpha Sorting Problem：
   Occurs when other transparent objects approach the edges of the mountain.
2. Rendering Surface First：
   Necessary to reveal the terrain surface, preventing the use of Early Z to reduce overdraw.
3. Only suitable from a god’s perspective
   When viewed from a perspective, issues may arise.

For those familiar with writing Terrain Shaders, it’s known that texture data is sourced from a control map combined with multiple splat maps. Interestingly, this concept can be extended to the handling of mountain edge transitions, achieving a smooth blend between the edge and the terrain. Regarding obtaining terrain texture data, the following process can be followed:

1. Pass the terrain’s control map and splat maps into the material of the mountain, including the terrain’s Bounds parameters (min, max points).
2. Define a range for the transition offset height (based on the terrain’s height, a parameter used by the Shader). Calculate the transition weight in the Shader based on the height. Blend terrain textures only when the height is below this threshold to optimize processing.
3. Calculate the corresponding UV coordinates using world coordinates’ xz and Bounds parameters. Sample the control map and access splat maps in a manner similar to a standard Terrain Shader.
4. Compute the final blended textures and normals based on the transition weight.

It’s important to note that the mentioned approach is tailored for completely flat terrains without any elevation changes. In such cases, the terrain’s normal can be assumed to be along the up axis, and the height is a constant value. For deformed terrains, additional terrain data, such as relevant normals and height information, is required. Unity’s terrain includes elevation data, and if you’re interested in blending transition processing for terrains with elevation changes, a solution can be found here:

OriginTerrainBlending