Street Fighter IV Volt 的 obm 檔案格式

OBM File Format in "Street Fighter IV Volt"

有同事向我提出想了解「Street Fighter IV Volt」的製作方法；於是我嘗試解開內裡的圖檔，發現跟「THE KING OF FIGHTERS-i」一樣使用了很多 obm 格式的檔案。我不知道 obm 是不是某遊戲引擎的格式。我為「THE KING OF FIGHTERS-i」編寫了一個工具，能把 obm 轉換為 PNG 檔案，用在「Street Fighter IV Volt」一樣沒有問題，肯定了兩個遊戲的 obm 格式是一樣。

obm 還會分至少三個格式，以 2-3 Bytes 來分辨。其中一個格式在圖寬及圖闊數據後，是 512 Bytes 的色盤數據，往後的才是像素數據。以下是目前為止的代碼：

 NSString *directory = [[NSBundle mainBundle] bundlePath];
 NSArray *array = [[NSFileManager defaultManager] contentsOfDirectoryAtPath:directory error:nil];

 for (NSString *filename in array)  {
  NSString *fileExtension = [[filename pathExtension] lowercaseString];
  if ([fileExtension isEqualToString:@"obm"] == NO)  {continue;}

  string = [directory stringByAppendingPathComponent:filename];
  NSData *data = [NSData dataWithContentsOfFile:string];
  unsigned char *dataBuffer = (unsigned char *)[data bytes];
  unsigned short *headerInfo = (unsigned short *)(dataBuffer);
  unsigned short *palette = (unsigned short *)(dataBuffer+8);

  int width = headerInfo[2];
  int height = headerInfo[3];
  unsigned char *imageBuffer = (unsigned char *)malloc((width*height)<<2);

  int imageType = headerInfo[1];
  switch (imageType)  {
   case 0x0801:
   case 0x0804:  {
    int sourceOffset = 8+512;
    int targetOffset = 0;

    for (int y=0; y<height; y++)  {
     for (int x=0; x<width; x++)  {
      unsigned char pixelByte = dataBuffer[sourceOffset];
      unsigned short paletteValue = palette[pixelByte];

      int alpha = (paletteValue&0x0001)<<7;
      int blue = (paletteValue&0x003e)<<2;
      int green = (paletteValue&0x07c0)>>3;
      int red = (paletteValue&0xf800)>>8;

      if (alpha != 0)  {alpha = 255;}

      //  0 = Blue
      //  1 = Green
      //  2 = Red
      //  3 = Alpha
      imageBuffer[targetOffset+0] = blue;
      imageBuffer[targetOffset+1] = green;
      imageBuffer[targetOffset+2] = red;
      imageBuffer[targetOffset+3] = alpha;
      
      targetOffset += 4;
      sourceOffset++;
     }
    }
   }  break;

   case 0x2001:  {
    memcpy(imageBuffer, palette, (width*height)<<2);

    for (int i=0; i<(width*height)<<2; i+=4)  {
     unsigned char red = imageBuffer[i+0];
     imageBuffer[i+0] = imageBuffer[i+2];
     imageBuffer[i+2] = red;
    }
   }  break;
  }

  image = [MainViewController raw2UIImage:imageBuffer width:width height:height];
  [currentImageView setImage:image];
  [currentImageView setFrame:CGRectMake(0, 0, width, height)];

  NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
  NSString *documentsDirectory = [paths objectAtIndex:0];
  string = [documentsDirectory stringByAppendingPathComponent:[NSString stringWithFormat:@"%@.png", filename]];
  [UIImagePNGRepresentation(image) writeToFile:string atomically:YES];
 }