[编辑器]Unity批量处理图片

加载图片，将其画在一张RenderTexture中，再新建一张Texture2D，从rt中读出来处理过的数据，再存进原路径中，

比如要将所有图片扩大1.5倍：

public static void ChangeSize(params string[] paths)
    {
        var texture2Ds = AssetDatabase.FindAssets ("t:Texture2D", paths);
        var retTexture = new Texture2D (1, 1, TextureFormat.ARGB32, false);
        int count = textures.Length;
        for(int i = 0; i < count; ++i)
        {
            var path = AssetDatabase.GUIDToAssetPath (textures[i]);
            var texture = AssetDatabase.LoadAssetAtPath<Texture2D> (path);
            var rt = RenderTexture.GetTemporary ((int)(texture.width * 1.5f), (int)(texture.height * 1.5f), 0, RenderTextureFormat.ARGB32);
            texture.DiscardContents ();
            Graphics.Blit (texture, rt);
            RenderTexture.active = texture;
            retTexture.Resize (rt.width, rt.height);
            retTexture.ReadPixels (new Rect (0, 0, rt.width, rt.height), 0, 0);
            retTexture.Apply ();
            File.WriteAllBytes (path, retTexture.EncodeToPNG ());
            RenderTexture.ReleaseTemporary (rt);
        }
        AssetDatabase.SaveAssets ();
        AssetDatabase.Refresh ();
    }

为防止重复编辑，可以在userdata中添加标志：

var im = AssetImporter.GetAtPath (path);
if (im.userData.Contains ("R2;"))
    continue;
im.userData += "R2;";