BoxTerrain.cs

using UnityEngine;
using UnityEditor;
using System.Collections;
using System.IO;

public class BoxTerrain : EditorWindow
{
	Texture2D texture = null;

	[MenuItem ("Editor/Box Terrain")]
	static public void Init()
	{
		BoxTerrain window = EditorWindow.GetWindow<BoxTerrain>();
	}

	void OnGUI()
	{
		EditorGUILayout.BeginHorizontal();

		if (GUILayout.Button("Load...", GUILayout.Width(100)))
		{
			string path = EditorUtility.OpenFilePanel("Select png", "", "png");

			if (path.Length != 0)
			{
				texture = new Texture2D(1, 1);
				texture.LoadImage(File.ReadAllBytes(path));
				texture.filterMode = FilterMode.Point;
				//texture = Resources.LoadAssetAtPath<Texture2D>(path);
				//texture = EditorGUIUtility.Load(path) as Texture2D;
			}
		}

		if (GUILayout.Button("Create Box", GUILayout.Width(100)))
		{
			var pixels = texture.GetPixels32();
			int width = texture.width;
			int height = texture.height;
			float offsetX = width * 0.5f;
			float offsetZ = height * 0.5f;
			for (int i = 0; i < height; i++)
			{
				for (int j = 0; j < width; j++)
				{
					int k = i * width + j;
					int y = pixels[k].r;

					if (y > 0)
					{
						int x = j;
						int z = i;
						var g = GameObject.CreatePrimitive(PrimitiveType.Cube);
						g.transform.position = new Vector3(x - offsetX, y * 0.5f, z - offsetZ);
						g.transform.localScale = new Vector3(1.0f, y, 1.0f);
						g.name = "Cube" + k.ToString();
						Undo.RegisterCreatedObjectUndo(g, "Create Box");
					}
				}
			}
		}

		EditorGUILayout.EndHorizontal();

		if (texture != null)
		{
			EditorGUI.DrawPreviewTexture(new Rect(25, 60, 100, 100), texture);
		}
	}
}