在不同平台下开发时，可能会遇到改变图片压缩格式的需求。这里把我之前实现的功能分享给各位。
可以学到的知识点如下：
- 拿到原始图片的大小
- 判断一个数是不是2的次幂
- 编辑器扩展之增加菜单按钮、显示对话框、显示进度条
- 安卓和IOS平台的图片压缩格式
public class TextureCompressOnPhone
{
private const string AndroidPlatformName = "Android";
private const string IOSPlatformName = "iPhone";
[MenuItem( "Tools/Android/CompressTexture" )]
private static void CompressTextureOnAndroid()
{
CompressInPlotform(AndroidPlatformName);
}
[MenuItem( "Tools/IOS/CompressTexture" )]
private static void CompressTextureOnIOS()
{
CompressInPlotform(IOSPlatformName);
}
private static void CompressInPlotform( string platform )
{
var message = "You are going to perform the following operation to ALL Texture2D! Continue?\n";
//弹出对话框进行二次确认
if (EditorUtility.DisplayDialog("Change Max Size", message, "OK", "Cancel") == false)
{
return;
}
// 显示进度条
EditorUtility.DisplayProgressBar("Change Max Size", "", 0.0f);
// 找到所有纹理
var guids = AssetDatabase.FindAssets("t:Texture2D");
for (int i = 0; i < guids.Length; i++)
{
var dialogTitle = "Change Max Size" + " (" + i + "/" + guids.Length + ")";
var progress = (float)i / guids.Length;
var guid = guids[i];
var path = AssetDatabase.GUIDToAssetPath(guid);
var go = AssetDatabase.LoadAssetAtPath<Texture2D>(path);
if (go == null)
{
continue;
}
EditorUtility.DisplayProgressBar(dialogTitle, go.name, progress);
//拿到TextureImporter才能对图片进行压缩
var assetImporter = AssetImporter.GetAtPath(path);
if (assetImporter != null)
{
var textureImporter = assetImporter as TextureImporter;
if (textureImporter == null)
{
Debug.LogWarningFormat(go, "MissingImporter Texture2D: '{0}'", go.name);
continue;
}
//拿到不压缩前的size
var defaultMaxSize = textureImporter.maxTextureSize;
TextureImporterPlatformSettings platformImporter = textureImporter.GetPlatformTextureSettings(platform);
platformImporter.overridden = true;
platformImporter.maxTextureSize = defaultMaxSize / 4;
var width = 0;
var height = 0;
//拿到宽高
GetTextureRealWidthAndHeight(textureImporter, ref width, ref height);
//判断有无alpha
var haveAlpha = textureImporter.DoesSourceTextureHaveAlpha();
platformImporter.format = GetCompressFormat(platform, width, height, haveAlpha);
textureImporter.SetPlatformTextureSettings(platformImporter);
EditorUtility.SetDirty(go);
Debug.LogFormat(go, "Processed Texture2D: '{0}'", go.name);
textureImporter.SaveAndReimport();
}
}
AssetDatabase.SaveAssets();
EditorUtility.ClearProgressBar();
}
// 得到目标压缩格式
private static TextureImporterFormat GetCompressFormat( string platform , int width, int height ,bool haveAlpha )
{
//分几种情况讨论，是不是2的次幂以及是不是有alpha通道
var isPowerOfTwo = WidthAndHeightIsPowerOfTwo(width, height);
if ( isPowerOfTwo == false )
{
if ( haveAlpha )
{
return TextureImporterFormat.RGBA16;
}
else
{
return TextureImporterFormat.RGB16;
}
}
else
{
if ( platform == AndroidPlatformName )
{
if( haveAlpha )
{
return TextureImporterFormat.ETC2_RGBA8Crunched;
}
else
{
return TextureImporterFormat.ETC_RGB4Crunched;
}
}
else if( platform == IOSPlatformName)
{
if( haveAlpha )
{
return TextureImporterFormat.PVRTC_RGBA4;
}
else
{
return TextureImporterFormat.PVRTC_RGB4;
}
}
}
return TextureImporterFormat.RGBA16;
}
// 判断宽和高是否是2的次幂
private static bool WidthAndHeightIsPowerOfTwo( int width, int height )
{
if ( IsPowerOfTwo(width) && IsPowerOfTwo(height) )
{
return true;
}
else
{
return false;
}
}
//用二进制与运算，如果一个数是2的次幂，n&(n-1) = 0
private static bool IsPowerOfTwo( int number )
{
if ( number <= 0 )
{
return false;
}
return ( number & ( number - 1 ) ) == 0;
}
//得到要压缩成几分之一，这里是二分之一
private static int GetCompressedMaxSize( int sourceMaxSize )
{
return sourceMaxSize / 2;
}
//用反射得到纹理宽高
public static void GetTextureRealWidthAndHeight( TextureImporter texImpoter, ref int width, ref int height )
{
System.Type type = typeof( TextureImporter );
System.Reflection.MethodInfo method = type.GetMethod( "GetWidthAndHeight", BindingFlags.Instance | BindingFlags.NonPublic );
var args = new object[] {
width, height };
method.Invoke( texImpoter, args );
width = (int)args[0];
height = (int)args[1];
}
}