Returns the alpha map at a position x, y given a width and height.

The returned array is three-dimensional - the first two dimensions represent x and y coordinates on the map, while the third denotes the splatmap texture to which the alphamap is applied.

// Add some random "noise" to the alphamaps.
function AddAlphaNoise(t: Terrain, noiseScale: float) {
	var maps = t.terrainData.GetAlphamaps(0, 0, t.terrainData.alphamapWidth, t.terrainData.alphamapHeight);
		for (var y = 0; y < t.terrainData.alphamapHeight; y++) {
			for (var x = 0; x < t.terrainData.alphamapWidth; x++) {
 			    var a0 = maps[x, y, 0];
				var a1 = maps[x, y, 1];
				
				a0 += Random.value * noiseScale;
				a1 += Random.value * noiseScale;
				
				var total = a0 + a1;
				
				maps[x, y, 0] = a0 / total;
				maps[x, y, 1] = a1 / total;
			}
		}
		
		t.terrainData.SetAlphamaps(0, 0, maps);
	}