Added Option to select the Source Channel of the Input Textures.

Editor/SmartTextureImporterEditor.cs

@@ -16,7 +16,11 @@ internal static class Styles
             EditorGUIUtility.TrTextContent("Alpha Channel", "This texture source channel will be packed into the Output texture alpha channel"),
         };
 
+        public static readonly GUIContent sourceTexture = EditorGUIUtility.TrTextContent("Source Texture", "The texture from which the channel will be extracted");
+        public static readonly GUIContent sourceChannel = EditorGUIUtility.TrTextContent("Source Channel", "The channel of the texture that should be extracted");
+
         public static readonly GUIContent invertColor = EditorGUIUtility.TrTextContent("Invert Color", "If enabled outputs the inverted color (1.0 - color)");
+
         public static readonly GUIContent readWrite = EditorGUIUtility.TrTextContent("Read/Write Enabled", "Enable to be able to access the raw pixel data from code.");
         public static readonly GUIContent generateMipMaps = EditorGUIUtility.TrTextContent("Generate Mip Maps");
         public static readonly GUIContent streamingMipMaps = EditorGUIUtility.TrTextContent("Streaming Mip Maps");
@@ -36,6 +40,7 @@ internal static class Styles
         };
 
         public static readonly string[] textureCompressionOptions = Enum.GetNames(typeof(TextureImporterCompression));
+        public static readonly string[] textureChannels = Enum.GetNames(typeof(TextureChannels));
         public static readonly string[] textureFormat = Enum.GetNames(typeof(TextureFormat));
         public static readonly string[] resizeAlgorithmOptions = Enum.GetNames(typeof(TextureResizeAlgorithm));
     }
@@ -121,11 +126,21 @@ void DrawInputTexture(int index)
         if (index < 0 || index >= 4)
             return;
 
-        EditorGUILayout.PropertyField(m_InputTextures[index], Styles.labelChannels[index]);
+        EditorGUILayout.LabelField(Styles.labelChannels[index], EditorStyles.boldLabel);
+        using (new EditorGUI.IndentLevelScope())
+        {
+            EditorGUILayout.PropertyField(m_InputTextures[index], Styles.sourceTexture);
+
+            SerializedProperty sourceChannel = m_InputTextureSettings[index].FindPropertyRelative("sourceChannel");
+            sourceChannel.intValue = EditorGUILayout.Popup(Styles.sourceChannel, sourceChannel.intValue, Styles.textureChannels);
 
         SerializedProperty invertColor = m_InputTextureSettings[index].FindPropertyRelative("invertColor");
         invertColor.boolValue = EditorGUILayout.Toggle(Styles.invertColor, invertColor.boolValue);
+
         EditorGUILayout.Space();
+
+        }
+
     }
 
     void DrawTextureImporterSettings()

Editor/TextureChannels.cs

@@ -0,0 +1,7 @@
+public enum TextureChannels
+{
+    Red,
+    Green,
+    Blue,
+    Alpha
+}

Runtime/TextureChannelPacker.cs

@@ -16,6 +16,11 @@ public struct TexturePackingSettings
     /// Outputs the inverted color (1.0 - color)
     /// </summary>
     public bool invertColor;
+
+    /// <summary>
+    /// Outputs the inverted color (1.0 - color)
+    /// </summary>
+    public int sourceChannel;
 }
 
 public static class TextureExtension
@@ -86,11 +91,24 @@ public static void PackChannels(this Texture2D mask, Texture2D[] textures, Textu
                 settings[2].invertColor ? 1.0f : 0.0f,
                 settings[3].invertColor ? 1.0f : 0.0f,
             };
+
+            int[] channelSource =
+            {
+                settings[0].sourceChannel,
+                settings[1].sourceChannel,
+                settings[2].sourceChannel,
+                settings[3].sourceChannel
+            };
+
             packChannelMaterial.SetTexture("_RedChannel", textures[0] != null ? textures[0] : Texture2D.blackTexture);
             packChannelMaterial.SetTexture("_GreenChannel", textures[1] != null ? textures[1] : Texture2D.blackTexture);
             packChannelMaterial.SetTexture("_BlueChannel", textures[2] != null ? textures[2] : Texture2D.blackTexture);
             packChannelMaterial.SetTexture("_AlphaChannel", textures[3] != null ? textures[3] : Texture2D.blackTexture);
             packChannelMaterial.SetVector("_InvertColor", new Vector4(invertColor[0], invertColor[1], invertColor[2], invertColor[3]));
+            packChannelMaterial.SetInt("_RedSource", channelSource[0]);
+            packChannelMaterial.SetInt("_GreenSource", channelSource[1]);
+            packChannelMaterial.SetInt("_BlueSource", channelSource[2]);
+            packChannelMaterial.SetInt("_AlphaSource", channelSource[3]);
 
             var rt = RenderTexture.GetTemporary(width, height, 0, RenderTextureFormat.ARGB32,
                 RenderTextureReadWrite.Linear);

Shaders/PackShader.shader

@@ -7,13 +7,21 @@
         _BlueChannel("BlueChannel", 2D) = "white" {}
         _AlphaChannel("AlphaChannel", 2D) = "white" {}
         _InvertColor("_InvertColor", Vector) = (0.0, 0.0, 0.0, 0.0)
+        _RedSource("_RedSource", Int) = 0
+        _GreenSource("_GreenSource", Int) = 0
+        _BlueSource("_BlueSource", Int) = 0
+        _AlphaSource("_AlphaSource", Int) = 0
     }
 
     HLSLINCLUDE
     Texture2D _RedChannel;
     Texture2D _GreenChannel;
     Texture2D _BlueChannel;
     Texture2D _AlphaChannel;
+    int _RedSource;
+    int _GreenSource;
+    int _BlueSource;
+    int _AlphaSource;
     sampler sampler_point_clamp;
 
     ENDHLSL
@@ -45,10 +53,30 @@
             half4 frag(float4 positionHCS : SV_POSITION) : SV_Target
             {
                 float2 uv = positionHCS * _RedChannel_TexelSize.xy;
-                half r = _RedChannel.Sample(sampler_point_clamp, uv).r;
-                half g = _GreenChannel.Sample(sampler_point_clamp, uv).r;
-                half b = _BlueChannel.Sample(sampler_point_clamp, uv).r;
-                half a = _AlphaChannel.Sample(sampler_point_clamp, uv).r;
+
+                half r =
+                    _RedSource == 0 ? _RedChannel.Sample(sampler_point_clamp, uv).r :
+                    _RedSource == 1 ? _RedChannel.Sample(sampler_point_clamp, uv).g :
+                    _RedSource == 2 ? _RedChannel.Sample(sampler_point_clamp, uv).b :
+                                      _RedChannel.Sample(sampler_point_clamp, uv).a;
+
+                half g =
+                    _GreenSource == 0 ? _GreenChannel.Sample(sampler_point_clamp, uv).r :
+                    _GreenSource == 1 ? _GreenChannel.Sample(sampler_point_clamp, uv).g :
+                    _GreenSource == 2 ? _GreenChannel.Sample(sampler_point_clamp, uv).b :
+                                        _GreenChannel.Sample(sampler_point_clamp, uv).a;
+
+                half b =
+                    _BlueSource == 0 ? _BlueChannel.Sample(sampler_point_clamp, uv).r :
+                    _BlueSource == 1 ? _BlueChannel.Sample(sampler_point_clamp, uv).g :
+                    _BlueSource == 2 ? _BlueChannel.Sample(sampler_point_clamp, uv).b :
+                                       _BlueChannel.Sample(sampler_point_clamp, uv).a;
+
+                half a =
+                    _AlphaSource == 0 ? _AlphaChannel.Sample(sampler_point_clamp, uv).r :
+                    _AlphaSource == 1 ? _AlphaChannel.Sample(sampler_point_clamp, uv).g :
+                    _AlphaSource == 2 ? _AlphaChannel.Sample(sampler_point_clamp, uv).b :
+                                        _AlphaChannel.Sample(sampler_point_clamp, uv).a;
 
                 if (_InvertColor.x > 0.0)
                     r = 1.0 - r;