Unity3d之剥离alpha通道

unity中, 将图集的 alpha 通道剥离出来可减少包体大小和内存使用大小。

方法是将原来的一张 rgba 图分成一张 rgb 和一张 alpha 图，android上rgb和alpha图均采用etc压缩格式，ios上采用pvrtc格式。其中alpha通道信息可以存在r中。

分享 alpha 通道工具的源代码如下：

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

 public static class TextureAlphaSpliter
 {
     const string
         RGBEndName = "(rgb)",
         AlphaEndName = "(a)";

     public static bool WhetherSplit = true;
     public static bool AlphaHalfSize;

     static Texture s_rgba;

     public static void SplitAlpha(Texture src, bool alphaHalfSize, out Texture rgb, out Texture alpha)
     {
         if (src == null)
             throw new ArgumentNullException("src");

         // make it readable
         string srcAssetPath = AssetDatabase.GetAssetPath(src);
         var importer = (TextureImporter)AssetImporter.GetAtPath(srcAssetPath);
         {
             importer.isReadable = true;
             importer.SetPlatformTextureSettings("Standalone", , TextureImporterFormat.ARGB32, , true);
             importer.SetPlatformTextureSettings("Android", , TextureImporterFormat.ARGB32, , true);
             importer.SetPlatformTextureSettings("iPhone", , TextureImporterFormat.ARGB32, , true);
         }
         AssetDatabase.ImportAsset(srcAssetPath);

         alpha = CreateAlphaTexture((Texture2D)src, alphaHalfSize);
         rgb = CreateRGBTexture(src);
     }

     static Texture CreateRGBTexture(Texture src)
     {
         if (src == null)
             throw new ArgumentNullException("src");

         string srcPath = AssetDatabase.GetAssetPath(src);
         string rgbPath = GetPath(src, RGBEndName);
         int size = Mathf.Max(src.width, src.height, );

         AssetDatabase.DeleteAsset(rgbPath);
         AssetDatabase.CopyAsset(srcPath, rgbPath);
         AssetDatabase.ImportAsset(rgbPath);

         SetSettings(rgbPath, size, TextureImporterFormat.ETC_RGB4, TextureImporterFormat.PVRTC_RGB4);

         return (Texture)AssetDatabase.LoadAssetAtPath(rgbPath, typeof(Texture));
     }

     static Texture CreateAlphaTexture(Texture2D src, bool alphaHalfSize)
     {
         if (src == null)
             throw new ArgumentNullException("src");

         // create texture
         var srcPixels = src.GetPixels();
         var tarPixels = new Color[srcPixels.Length];
         for (int i = ; i < srcPixels.Length; i++)
         {
             float r = srcPixels[i].a;
             tarPixels[i] = new Color(r, r, r);
         }

         Texture2D alphaTex = new Texture2D(src.width, src.height, TextureFormat.ARGB32, false);
         alphaTex.SetPixels(tarPixels);
         alphaTex.Apply();

         // save
         string saveAssetPath = GetPath(src, AlphaEndName);
         string fullPath = BuildingAssetBundle.GetFullPath(saveAssetPath);
         var bytes = alphaTex.EncodeToPNG();
         File.WriteAllBytes(fullPath, bytes);

         AssetDatabase.SaveAssets();
         AssetDatabase.Refresh();

         // setting
         int size = alphaHalfSize ? Mathf.Max(src.width / , src.height / , ) : Mathf.Max(src.width, src.height, );
         SetSettings(saveAssetPath, size, TextureImporterFormat.ETC_RGB4, TextureImporterFormat.PVRTC_RGB4);

         return (Texture)AssetDatabase.LoadAssetAtPath(saveAssetPath, typeof(Texture));
     }

     static void SetSettings(string assetPath, int maxSize, TextureImporterFormat androidFormat, TextureImporterFormat iosFormat)
     {
         var importer = (TextureImporter)AssetImporter.GetAtPath(assetPath);
         {
             importer.npotScale = TextureImporterNPOTScale.ToNearest;
             importer.isReadable = false;
             importer.mipmapEnabled = false;
             importer.alphaIsTransparency = false;
             importer.wrapMode = TextureWrapMode.Clamp;
             importer.filterMode = FilterMode.Bilinear;
             importer.anisoLevel = ;
             importer.SetPlatformTextureSettings("Android", maxSize, androidFormat, , true);
             importer.SetPlatformTextureSettings("iPhone", maxSize, iosFormat, , true);
             importer.SetPlatformTextureSettings("Standalone", maxSize, TextureImporterFormat.ARGB32, , true);
         }
         AssetDatabase.ImportAsset(assetPath);
     }

     static string GetPath(Texture src, string endName)
     {
         if (src == null)
             throw new ArgumentNullException("src");

         string srcAssetPath = AssetDatabase.GetAssetPath(src);
         if (string.IsNullOrEmpty(srcAssetPath))
             return null;

         string dirPath = Path.GetDirectoryName(srcAssetPath);
         string ext = Path.GetExtension(srcAssetPath);
         string fileName = Path.GetFileNameWithoutExtension(srcAssetPath);

         if (fileName.EndsWith(RGBEndName))
             fileName = fileName.Substring(, fileName.Length - RGBEndName.Length);

         if (fileName.EndsWith(AlphaEndName))
             fileName = fileName.Substring(, fileName.Length - AlphaEndName.Length);

         return string.Format("{0}/{1}{2}{3}", dirPath, fileName, endName ?? "", ext);
     }

     public static Texture GetRGBA(Texture src)
     {
         if (src != null && (s_rgba == null || s_rgba.name != src.name))
         {
             string path = GetPath(src, "");
             if (!string.IsNullOrEmpty(path))
                 s_rgba = AssetDatabase.LoadAssetAtPath(path, typeof(Texture)) as Texture;
         }

         return s_rgba;
     }
 }

SplitAlpha

然后改造一下 shader，以ngui的shader为例。

原来要用一张 rgba 图的地方，现在改成用两张图，一张 rgb 和一张 alpha，改造为下：

Shader "Custom/Alpha Splited Colored"
{
    Properties
    {
        _MainTex ("RGB", 2D) = "black" {}
        _AlphaTex ("Alpha", 2D) = "black" {}
    }

    SubShader
    {
        LOD 

        Tags
        {
            "Queue" = "Transparent"
            "IgnoreProjector" = "True"
            "RenderType" = "Transparent"
        }

        Pass
        {
            Cull Off
            Lighting Off
            ZWrite Off
            Fog { Mode Off }
            Offset -, -
            Blend SrcAlpha OneMinusSrcAlpha

            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag            

            sampler2D _MainTex;
            sampler2D _AlphaTex;

            struct appdata_t
            {
                float4 vertex : POSITION;
                float2 texcoord : TEXCOORD0;
                fixed4 color : COLOR;
            };

            struct v2f
            {
                float4 vertex : SV_POSITION;
                half2 texcoord : TEXCOORD0;
                fixed4 color : COLOR;
            };

            v2f vert (appdata_t v)
            {
                v2f o;
                o.vertex = mul(UNITY_MATRIX_MVP, v.vertex);
                o.texcoord = v.texcoord;
                o.color = v.color;
                return o;
            }

            fixed4 frag (v2f IN) : COLOR
            {
                // [dev]
                fixed4 col;
                col.rgb = tex2D(_MainTex, IN.texcoord).rgb;
                col.a = tex2D(_AlphaTex, IN.texcoord).r;

                if (IN.color.r < 0.001 && IN.color.g < 0.001 && IN.color.b < 0.001)
                {
                    float grey = dot(col.rgb, float3(0.299, 0.587, 0.114));
                    col.rgb = float3(grey, grey, grey);
                }
                else
                    col = col * IN.color;

                return col;
            }
            ENDCG
        }
    }

    SubShader
    {
        LOD 

        Tags
        {
            "Queue" = "Transparent"
            "IgnoreProjector" = "True"
            "RenderType" = "Transparent"
        }

        Pass
        {
            Cull Off
            Lighting Off
            ZWrite Off
            Fog { Mode Off }
            Offset -, -
            ColorMask RGB
            Blend SrcAlpha OneMinusSrcAlpha
            ColorMaterial AmbientAndDiffuse

            SetTexture [_MainTex]
            {
                Combine Texture * Primary
            }

            SetTexture [_AlphaTex]
            {
                Combine previous, texture * primary
            }
        }
    }
}

shader

转载请注明出处：http://www.cnblogs.com/jietian331/p/5167422.html