TerrainInfoHelper.cs

using UnityEngine;

public class TerrainInfoHelper
{
    private static float[] GetTextureMix(
        Vector3 worldPos)
    {
        // returns an array containing the relative mix of textures
        // on the main terrain at this world position.
        // The number of values in the array will equal the number
        // of textures added to the terrain.
        var terrain = Terrain.activeTerrain;
        var terrainData = terrain.terrainData;
        var terrainPos = terrain.transform.position;
        // calculate which splat map cell the worldPos falls within (ignoring y)
        var mapX = (int) (((worldPos.x - terrainPos.x) / terrainData.size.x) * terrainData.alphamapWidth);
        var mapZ = (int) (((worldPos.z - terrainPos.z) / terrainData.size.z) * terrainData.alphamapHeight);
        // get the splat data for this cell as a 1x1xN 3d array (where N = number of textures)
        var splatmapData = terrainData.GetAlphamaps(
            mapX,
            mapZ,
            1,
            1);
        // extract the 3D array data to a 1D array:
        var cellMix = new float[splatmapData.GetUpperBound(
            2) + 1];
        for (var n = 0; n < cellMix.Length; ++n)
        {
            cellMix[
                n
            ] = splatmapData[
                0,
                0,
                n
            ];
        }

        return cellMix;
    }

    public static int GetMainTexture(
        Vector3 worldPos)
    {
        // returns the zero-based index of the most dominant texture
        // on the main terrain at this world position.
        var mix = GetTextureMix(
            worldPos);
        float maxMix = 0;
        var maxIndex = 0;
        // loop through each mix value and find the maximum
        for (var n = 0; n < mix.Length; ++n)
        {
            if (!(mix[
                n
            ] > maxMix)) continue;
            maxIndex = n;
            maxMix = mix[
                n
            ];
        }

        return maxIndex;
    }
}