TerrainData.SetAlphamaps

Description

Assign all splat values in the given map area.

The array supplied to this function determines the width and height of the portion to be replaced. The third dimension of the array corresponds to the number of splatmap textures.

using UnityEngine;

public class Example : MonoBehaviour
{
    public Terrain t;
    // Blend the two terrain textures according to the steepness of
    // the slope at each point.
    void Start()
    {
        float[,,] map = new float[t.terrainData.alphamapWidth, t.terrainData.alphamapHeight, 2];

        // For each point on the alphamap...
        for (int y = 0; y < t.terrainData.alphamapHeight; y++)
        {
            for (int x = 0; x < t.terrainData.alphamapWidth; x++)
            {
                // Get the normalized terrain coordinate that
                // corresponds to the the point.
                float normX = x * 1.0f / (t.terrainData.alphamapWidth - 1);
                float normY = y * 1.0f / (t.terrainData.alphamapHeight - 1);

                // Get the steepness value at the normalized coordinate.
                var angle = t.terrainData.GetSteepness(normX, normY);

                // Steepness is given as an angle, 0..90 degrees. Divide
                // by 90 to get an alpha blending value in the range 0..1.
                var frac = angle / 90.0;
                map[x, y, 0] = (float)frac;
                map[x, y, 1] = (float)(1 - frac);
            }
        }
        t.terrainData.SetAlphamaps(0, 0, map);
    }
}