add lossless flag

WebpDirConv/Program.cs

@@ -1,9 +1,9 @@
 using System.Diagnostics;
 
 
-if (args.Length != 2)
+if (args.Length < 2)
 {
-    Console.WriteLine("Err: 2 args required, <inputDir> <outputDir>");
+    Console.WriteLine("Err: at least 2 args required, <inputDir> <outputDir> [-lossless]");
     return 1;
 }
 
@@ -22,6 +22,20 @@ if (!Directory.Exists(outputDir))
     return 1;
 }
 
+var flagLossLess = false;
+
+if (args.Length > 2)
+{
+    if (args[2] == "-lossless")
+    {
+        flagLossLess = true;
+    }
+    else
+    {
+        Console.WriteLine("Warn: invalid arg#3, should be [-lossless], set lossless flag to false");
+    }
+}
+
 Process.GetCurrentProcess().PriorityClass = ProcessPriorityClass.Idle;
 
 var fullInputDir = Path.GetFullPath(inputDir);
@@ -60,6 +74,8 @@ void ProcessFunc(string inputFilePath)
         }
     };
 
+    if (flagLossLess) pWebp.StartInfo.ArgumentList.Add("-lossless");
+
     pWebp.Start();
     pWebp.WaitForExit();