NGUI打图集工具Alpha通道分离

工具设计目的

NGUI中图集默认使用"Unlit/Transparent Colored" Shader来创建材质。这样的话需要一张RGBA32的带透明通道的贴图，一张515x512的图占用空间1M，加载到内存后变成2M。在手机内存还是比较宝贵的时代这个是不大能接受的。一般项目的做法是分隔成两张图一张color图包含RGB通道，一张alpha图包含A通道。通过shader来组合长RGBA的图，来实现接近于RGBA的效果。通常Android使用ETC格式，IOS使用PVRTC格式。一张ETC格式的512x512的图占用128kb，两张一起256kb。这样相对于RGBA32格式的只占用其四分之一的空间。

NGUI自带的图集工具并不支持打ETC通道分离。通常一般做法采用第三方工具TexturePacker来做这个，但是使用第三方工具来做这个也会比较麻烦。所以通过修改NGUI打图集工具来实现这个通道分离。

图集增加通道分离

通道分离的做法是生成一张完整RGBA32的图片，然后读取RGBA分别生成两张和RGBA32一样大小的RGB图片和Alpha图片。最后替换shader，生成两张图片合成的材质 。代码如下：

using UnityEngine;
using System.Collections;
using UnityEditor;
using System.Collections.Generic;
using System.IO;
using com.geargames.common.utils;

public class UIAtlasChangeShaderTool : EditorWindow
{
    private bool _mSearched;
    private Object[] mObjects;
    private Vector2 mScroll = Vector2.zero;
    public static bool useAlpha = true;
    const string defShader = "Unlit/Transparent Colored";
    const string newShader = "这里填合成两张图的shader名字";

    private readonly string[] atlasPaths = { "这里填图集所在路径"};

    [MenuItem("Tool/Open UIAtlas Shader Change Window")]
    public static void OpenWindow()
    {
        UIAtlasChangeShaderTool window = (UIAtlasChangeShaderTool)EditorWindow.GetWindow(typeof(UIAtlasChangeShaderTool));
        window.Show();
    }
    void OnGUI()
    {
        if (mObjects != null && mObjects.Length != 0)
        {
            mScroll = GUILayout.BeginScrollView(mScroll);
            foreach (Object o in mObjects)
            {
                DrawUIAtalsObject(o);
            }
            GUILayout.EndScrollView();
        }
        GUILayout.Space(6f);
        GUILayout.BeginHorizontal();
        GUILayout.FlexibleSpace();
        bool search = GUILayout.Button("Show All", "LargeButton", GUILayout.Width(120f));
        bool Normal = GUILayout.Button("Normal All", "LargeButton", GUILayout.Width(120f));
        bool Etc = GUILayout.Button("Etc All", "LargeButton", GUILayout.Width(120f));
        bool CreateTexture = GUILayout.Button("CreateTexture All", "LargeButton", GUILayout.Width(200f));
        GUILayout.FlexibleSpace();
        GUILayout.EndHorizontal();
        if (search) Search(typeof(UIAtlas));

        if (mObjects == null || mObjects.Length == 0) return;
        if (Normal) foreach (Object o in mObjects) _ChangeShaderToNormal(o as UIAtlas);
        if (Etc) foreach (Object o in mObjects) _ChangeShaderToEtc(o as UIAtlas);
        if (CreateTexture)foreach (Object o in mObjects) SeperateRGBAandlphaChannel((o as UIAtlas).spriteMaterial.mainTexture as Texture2D);
    }

    private void DrawUIAtalsObject(Object obj)
    {
        if (obj == null) return;
        Component comp = obj as Component;
        UIAtlas at = obj as UIAtlas;
        GUILayout.BeginHorizontal();
        {
            string path = AssetDatabase.GetAssetPath(obj);

            if (string.IsNullOrEmpty(path))
            {
                path = "[Embedded]";
                GUI.contentColor = new Color(0.7f, 0.7f, 0.7f);
            }
            else if (comp != null && EditorUtility.IsPersistent(comp.gameObject))
                GUI.contentColor = new Color(0.6f, 0.8f, 1f);

            GUILayout.Label(obj.name, "TextArea", GUILayout.Width(160f), GUILayout.Height(20f));
            GUILayout.Label(path.Replace("Assets/", ""), "TextArea", GUILayout.Width(300f), GUILayout.Height(20f));
            GUILayout.Label(at.spriteMaterial.shader.name, "TextArea", GUILayout.Width(200f), GUILayout.Height(20f));
            GUI.contentColor = Color.white;
            if (GUILayout.Button("Normal", "ButtonLeft", GUILayout.Width(60f), GUILayout.Height(16f)))
            {
                _ChangeShaderToNormal(at);
                AssetDatabase.Refresh();
            }

            if (GUILayout.Button("Etc", "ButtonLeft", GUILayout.Width(60f), GUILayout.Height(16f)))
            {
                _ChangeShaderToEtc(at);
                AssetDatabase.Refresh();
            }
            
            if (GUILayout.Button("CreateTexture", "ButtonLeft", GUILayout.Width(100f), GUILayout.Height(16f)))
            {
               string assetPath =  AssetDatabase.GetAssetPath(at).Replace(".prefab",".png")  ;
                Texture2D texture = AssetDatabase.LoadAssetAtPath(assetPath,typeof(Texture2D)) as Texture2D;
                SeperateRGBAandlphaChannel(at.texture as Texture2D);
                AssetDatabase.Refresh();
            }
        }
        GUILayout.EndHorizontal();

    }
    protected void Search(System.Type mType)
    {
        _mSearched = true;
        List pathList = new List();
        _GetAllAtlasPath(pathList);
        bool isComponent = mType.IsSubclassOf(typeof(Component));
        List