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", 4096, TextureImporterFormat.ARGB32, 100, true);
            importer.SetPlatformTextureSettings("Android", 4096, TextureImporterFormat.ARGB32, 100, true);
            importer.SetPlatformTextureSettings("iPhone", 4096, TextureImporterFormat.ARGB32, 100, 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, 32);

        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 = 0; 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 / 2, src.height / 2, 32) : Mathf.Max(src.width, src.height, 32);
        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 = 4;
            importer.SetPlatformTextureSettings("Android", maxSize, androidFormat, 100, true);
            importer.SetPlatformTextureSettings("iPhone", maxSize, iosFormat, 100, true);
            importer.SetPlatformTextureSettings("Standalone", maxSize, TextureImporterFormat.ARGB32, 100, 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(0, fileName.Length - RGBEndName.Length);

        if (fileName.EndsWith(AlphaEndName))
            fileName = fileName.Substring(0, 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;
    }
}

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 200

        Tags
        {
            "Queue" = "Transparent"
            "IgnoreProjector" = "True"
            "RenderType" = "Transparent"
        }
        
        Pass
        {
            Cull Off
            Lighting Off
            ZWrite Off
            Fog { Mode Off }
            Offset -1, -1
            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 100

        Tags
        {
            "Queue" = "Transparent"
            "IgnoreProjector" = "True"
            "RenderType" = "Transparent"
        }
        
        Pass
        {
            Cull Off
            Lighting Off
            ZWrite Off
            Fog { Mode Off }
            Offset -1, -1
            ColorMask RGB
            Blend SrcAlpha OneMinusSrcAlpha
            ColorMaterial AmbientAndDiffuse
            
            SetTexture [_MainTex]
            {
                Combine Texture * Primary
            }

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

 

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