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