Unity工程里图片的RGB和Alpha通道的分离，以及显示所有带有Alpha通道贴图的Material

背景：ETC1图片格式的罪孽，不支持Alpha通道。于是程序员们将一些气力浪费在Alpha通道的处理上。 为了能使用ETC1，同时某些透明效果必须有Alpha通道，一般的处理方式是将RGB和Alpha分为两张图片分别储存。 只存Alpha通道的图片及RGB都为要存的Alpha值，因为熵比较小，图片尺寸也可以相应减小一些。

要做的工作：

1. 将带有Alpha通道的图片，另存为两张图片，一张只存RGB信息，另一张只存Alpha信息。建议保持为图片原目录，名称加后缀“_RGB”, "_Alpha"。

2. 带有Alpha通道的图片，所用的Shader要更新为支持RGB和Alpha信息分别从两张不同图片读取的shader。这个功能，因为不能的Material的Shader会很不一样，因此，不用程序来强硬指定了。但程序起码需要给出提示，工程中哪些Material用到了哪些带有Alpha通道的图片。

不罗嗦了，直接上代码。

using UnityEngine;using System.Collections;using System.Collections.Generic;using UnityEditor;using System.IO;using System.Reflection;public class MaterialTextureForETC1{public static float sizeScale = 0.5f;   //the size decrease scale for alphaTexturepublic static Dictionary<string, bool> texturesAlphaDic = new Dictionary<string, bool>();[MenuItem("EffortForETC1/Seperate RGB and Alpha Channel for All Textures")]static void SeperateAllTexturesRGBandAlphaChannel(){string[] paths = Directory.GetFiles(Application.dataPath, "*.*", SearchOption.AllDirectories);foreach (string path in paths){if (!string.IsNullOrEmpty(path) && IsTextureFile(path))   //full name{SeperateRGBAandlphaChannel(path);}} }[MenuItem("EffortForETC1/Show Materials Having Textures with Alpha Chanel")]static void ShowMaterialsHavingTextureswithAlphaChanel(){CalculateTexturesAlphaChannelDic();string[] matpaths = Directory.GetFiles(Application.dataPath, "*.mat", SearchOption.AllDirectories);foreach (string matpath in matpaths){string propermatpath = GetRelativeAssetPath(matpath);Material mat = (Material)AssetDatabase.LoadAssetAtPath(propermatpath, typeof(Material));if (mat){string[] alphatexpaths = GetMaterialTexturesHavingAlphaChannel(mat);if (alphatexpaths.Length == 0){continue;}Debug.Log("Material having texture(s) with Alpha channel : " + propermatpath);foreach (string alphatexpath in alphatexpaths){Debug.Log(alphatexpath + " in " + propermatpath);}}else{Debug.LogError("Load material failed : " + matpath);}}Debug.Log("Finish!");     }#region inspect materialstatic string[] GetMaterialTexturesHavingAlphaChannel(Material _mat){List<string> alphatexpaths = new List<string>();string[] texpaths = GetMaterialTexturePaths(_mat);foreach (string texpath in texpaths){if (texturesAlphaDic[texpath]){alphatexpaths.Add(texpath);}}return alphatexpaths.ToArray();}static string[] GetMaterialTexturePaths(Material _mat){List<string> results = new List<string>();Object[] roots = new Object[] { _mat };Object[] dependObjs = EditorUtility.CollectDependencies(roots);foreach (Object dependObj in dependObjs){if (dependObj.GetType() == typeof(Texture2D)){string texpath = AssetDatabase.GetAssetPath(dependObj.GetInstanceID());results.Add(texpath);}}return results.ToArray();}#endregionstatic void CalculateTexturesAlphaChannelDic(){string[] paths = Directory.GetFiles(Application.dataPath, "*.*", SearchOption.AllDirectories);foreach (string path in paths){if (!string.IsNullOrEmpty(path) && IsTextureFile(path))   //full name{string assetRelativePath = GetRelativeAssetPath(path);SetTextureReadable(assetRelativePath);Texture2D sourcetex = AssetDatabase.LoadAssetAtPath(assetRelativePath, typeof(Texture2D)) as Texture2D;  if (!sourcetex)  //make sure the file is really Texture2D which can be loaded as Texture2D.{continue;}if (HasAlphaChannel(sourcetex)){AddValueToDic(assetRelativePath, true);                                    }else{AddValueToDic(assetRelativePath, false);  }}} }static void AddValueToDic(string _key, bool _val){if (texturesAlphaDic.ContainsKey(_key)){texturesAlphaDic[_key] = _val;}else{texturesAlphaDic.Add(_key, _val);}}#region process texturestatic void SeperateRGBAandlphaChannel(string _texPath){string assetRelativePath = GetRelativeAssetPath(_texPath);SetTextureReadable(assetRelativePath);Texture2D sourcetex = AssetDatabase.LoadAssetAtPath(assetRelativePath, typeof(Texture2D)) as Texture2D;  //not just the textures under Resources fileif (!sourcetex){Debug.Log("Load Texture Failed : " + assetRelativePath);return;}if (!HasAlphaChannel(sourcetex)){Debug.Log("Texture does not have Alpha channel : " + assetRelativePath);return;}Texture2D rgbTex = new Texture2D(sourcetex.width, sourcetex.height, TextureFormat.RGB24, true);Texture2D alphaTex = new Texture2D((int)(sourcetex.width * sizeScale), (int)(sourcetex.height * sizeScale), TextureFormat.RGB24, true);for (int i = 0; i < sourcetex.width; ++i)for (int j = 0; j < sourcetex.height; ++j){Color color = sourcetex.GetPixel(i, j);Color rgbColor = color;Color alphaColor = color;alphaColor.r = color.a;alphaColor.g = color.a;alphaColor.b = color.a;rgbTex.SetPixel(i, j, rgbColor);alphaTex.SetPixel((int)(i * sizeScale), (int)(j * sizeScale), alphaColor);}rgbTex.Apply();alphaTex.Apply();byte[] bytes = rgbTex.EncodeToPNG();File.WriteAllBytes(GetRGBTexPath(_texPath), bytes);bytes = alphaTex.EncodeToPNG();File.WriteAllBytes(GetAlphaTexPath(_texPath), bytes);Debug.Log("Succeed to seperate RGB and Alpha channel for texture : " + assetRelativePath);}static bool HasAlphaChannel(Texture2D _tex){for (int i = 0; i < _tex.width; ++i)for (int j = 0; j < _tex.height; ++j){Color color = _tex.GetPixel(i, j);float alpha = color.a;if (alpha < 1.0f - 0.001f){return true;}}return false;}static void SetTextureReadable(string _relativeAssetPath){string postfix = GetFilePostfix(_relativeAssetPath);if (postfix == ".dds")    // no need to set .dds file.  Using TextureImporter to .dds file would get casting type error.{return;}TextureImporter ti = (TextureImporter)TextureImporter.GetAtPath(_relativeAssetPath);ti.isReadable = true;AssetDatabase.ImportAsset(_relativeAssetPath);}#endregion#region string or path helperstatic bool IsTextureFile(string _path){string path = _path.ToLower();return path.EndsWith(".psd") || path.EndsWith(".tga") || path.EndsWith(".png") || path.EndsWith(".jpg") || path.EndsWith(".dds") || path.EndsWith(".bmp") || path.EndsWith(".tif") || path.EndsWith(".gif");}static string GetRGBTexPath(string _texPath){return GetTexPath(_texPath, "_RGB.");}static string GetAlphaTexPath(string _texPath){return GetTexPath(_texPath, "_Alpha.");}static string GetTexPath(string _texPath, string _texRole){string result = _texPath.Replace(".", _texRole);string postfix = GetFilePostfix(_texPath);return result.Replace(postfix, ".png");}static string GetRelativeAssetPath(string _fullPath){_fullPath = GetRightFormatPath(_fullPath);int idx = _fullPath.IndexOf("Assets");string assetRelativePath = _fullPath.Substring(idx);return assetRelativePath;}static string GetRightFormatPath(string _path){return _path.Replace("\\", "/");}static string GetFilePostfix(string _filepath)   //including '.' eg ".tga", ".dds"{string postfix = "";int idx = _filepath.LastIndexOf('.');if (idx > 0 && idx < _filepath.Length)postfix = _filepath.Substring(idx, _filepath.Length - idx);return postfix;}#endregion   }

这篇文章里有两个明显的问题：
1. 处理Alpha贴图时是一个像素一个像素地处理，用Texture.SetPixel()函数。推荐批量处理，用Texture.SetPixels()函数。推荐批量处理，用Texture.SetPixels()函数。
2. Alpha贴图只存储Alpha通道信息，信息熵较低，理论上可以缩减一些尺寸来存储，但简单地按比例缩小可能会有问题，例如Alpha通道像素相邻一直为黑白黑白的情况，会严重失真，这里的取样需要考虑下。

【改进版】Unity工程里图片的RGB和Alpha通道的分离

http://blog.csdn.net/e295166319/article/details/52624155