Read hidden alpha image in wii textures

Author: PikminGuts92

Src/Core/Mackiloha.App/Extensions/TextureExtensions.cs

@@ -45,16 +45,47 @@ public static byte[] ToRGBA(this HMXBitmap bitmap, SystemInfo info)
             case TPL_CMP_2:
             case TPL_CMP_ALPHA:
                 // Wii textures
-                var tempData = new byte[((bitmap.Width * bitmap.Height) * bitmap.Bpp) / 8]; // Just ignore mips
-                Array.Copy(bitmap.RawData, tempData, tempData.Length);
+                if (bitmap.Bpp == 4 && bitmap.WiiAlphaNumber == 4)
+                {
+                    // Hidden alpha texture after mips... ugh
+                    var dxSize = (bitmap.Width * bitmap.Height * bitmap.Bpp) / 8;
+
+                    var rgbData = new byte[dxSize];
+                    var alphaData = new byte[dxSize];
+
+                    Array.Copy(bitmap.RawData, 0, rgbData, 0, rgbData.Length);
+                    Array.Copy(bitmap.RawData, bitmap.RawData.Length - rgbData.Length, alphaData, 0, alphaData.Length);
+
+                    // Remap blocks to DXT1
+                    Texture.TPL.TPLToDXT1(bitmap.Width, bitmap.Height, rgbData);
+                    Texture.TPL.TPLToDXT1(bitmap.Width, bitmap.Height, alphaData);
+
+                    // Decode both images
+                    var decodedImage = DecodeDxImage(rgbData, bitmap.Width, bitmap.Height, 0, DxEncoding.DXGI_FORMAT_BC1_UNORM);
+                    var decodedAlpha = DecodeDxImage(alphaData, bitmap.Width, bitmap.Height, 0, DxEncoding.DXGI_FORMAT_BC1_UNORM);
 
-                if (bitmap.Bpp == 4)
+                    // Combine alpha channel
+                    for (int i = 0; i < decodedImage.Length; i += 4)
+                    {
+                        // Load from green channel
+                        decodedImage[i + 3] = decodedAlpha[i + 1];
+                    }
+
+                    return decodedImage;
+                }
+                else if (bitmap.Bpp == 4)
                 {
+                    var tempData = new byte[((bitmap.Width * bitmap.Height) * bitmap.Bpp) / 8]; // Just ignore mips
+                    Array.Copy(bitmap.RawData, tempData, tempData.Length);
+
                     Texture.TPL.TPLToDXT1(bitmap.Width, bitmap.Height, tempData);
                     return DecodeDxImage(tempData, bitmap.Width, bitmap.Height, 0, DxEncoding.DXGI_FORMAT_BC1_UNORM);
                 }
                 else
                 {
+                    var tempData = new byte[((bitmap.Width * bitmap.Height) * bitmap.Bpp) / 8]; // Just ignore mips
+                    Array.Copy(bitmap.RawData, tempData, tempData.Length);
+
                     // 8bpp wii texture is actually two DXT1 textures
                     var rgbData = tempData.AsSpan(0, tempData.Length / 2);
                     var alphaData = tempData.AsSpan(tempData.Length / 2, tempData.Length / 2);
@@ -70,6 +101,7 @@ public static byte[] ToRGBA(this HMXBitmap bitmap, SystemInfo info)
                     // Combine alpha channel
                     for (int i = 0; i < decodedImage.Length; i += 4)
                     {
+                        // Load from green channel
                         decodedImage[i + 3] = decodedAlpha[i + 1];
                     }
 

Src/Core/Mackiloha/HMXBitmap.cs

@@ -9,6 +9,7 @@ public class HMXBitmap : ISerializable
     public int Width { get; set; }
     public int Height { get; set; }
     public int BPL { get; set; }
+    public int WiiAlphaNumber { get; set; }
 
     public byte[] RawData { get; set; }
 }

Src/Core/Mackiloha/IO/Serializers/HMXBitmapSerializer.cs

@@ -20,9 +20,10 @@ public override void ReadFromStream(AwesomeReader ar, ISerializable data)
         bitmap.Width = ar.ReadUInt16();
         bitmap.Height = ar.ReadUInt16();
         bitmap.BPL = ar.ReadUInt16();
+        bitmap.WiiAlphaNumber = ar.ReadUInt16(); // Assuming u16
 
-        ar.BaseStream.Position += 19; // Skips zeros
-        bitmap.RawData = ar.ReadBytes(CalculateTextureByteSize(bitmap.Encoding, bitmap.Width, bitmap.Height, bitmap.Bpp, bitmap.MipMaps));
+        ar.BaseStream.Position += 17; // Skips zeros
+        bitmap.RawData = ar.ReadBytes(CalculateTextureByteSize(bitmap.Encoding, bitmap.Width, bitmap.Height, bitmap.Bpp, bitmap.MipMaps, bitmap.WiiAlphaNumber));
     }
 
     public override void WriteToStream(AwesomeWriter aw, ISerializable data)
@@ -46,7 +47,7 @@ public override void WriteToStream(AwesomeWriter aw, ISerializable data)
         aw.Write(bytes);
     }
 
-    private int CalculateTextureByteSize(int encoding, int w, int h, int bpp, int mips)
+    private int CalculateTextureByteSize(int encoding, int w, int h, int bpp, int mips, int wiiAlphaNum = 0)
     {
         int bytes = 0;
 
@@ -62,6 +63,12 @@ private int CalculateTextureByteSize(int encoding, int w, int h, int bpp, int mi
                 // Each color is 32 bits 
                 bytes += (bpp == 4 || bpp == 8) ? 1 << (bpp + 2) : 0;
                 break;
+            case 72: // Wii 4bpp texture
+                if (wiiAlphaNum == 4)
+                {
+                    bytes += (w * h * bpp) / 8;
+                }
+                break;
         }
 
         while (mips >= 0)