/// <summary>
/// Decode the volume resource map.
/// </summary>
/// <param name="data">Resource map data.</param>
/// <param name="startOffset">Start offset in resource map data.</param>
/// <param name="length">Length of resource map data (in bytes).</param>
/// <param name="resourceMapEntries">Resource map entry collection to add decoded entries to.</param>
internal static void ReadResourceMap(byte[] data, int startOffset, int length, VolumeResourceMapEntryCollection resourceMapEntries)
{
int count = length / 3;
if (count > 255)
{
// There can't be more than 255 resources for a particular type of resource
// If the resource map is longer than that, it is probably padded with junk
count = 255;
}
for (int index = 0; index < count; index++)
{
int dataOffset = startOffset + (index * 3);
byte b0 = data[dataOffset + 0];
byte b1 = data[dataOffset + 1];
byte b2 = data[dataOffset + 2];
// [0][1][2] = volume file number and position in that volume file
// [0] = 76543210 [1] = 76543210 [2] = 76543210
// [0] = VVVVPPPP [1] = PPPPPPPP [2] = PPPPPPPP
// When all three bytes are 0xff it means the resource doesn't exist
if (!(b0 == 0xff && b1 == 0xff && b2 == 0xff))
{
int volume = (b0 & 0xf0) >> 4;
int resOffset = ((b0 & 0x0f) * 0x10000) + (b1 * 0x100) + b2;
var entry = new VolumeResourceMapEntry((byte)index, (byte)volume, resOffset);
resourceMapEntries.Add(entry);
}
}
}
/// <summary>
/// Extract the resource from the volume.
/// </summary>
/// <param name="container">Game container.</param>
/// <param name="fileName">Volume file name.</param>
/// <param name="dirEntry">Resource map entry for the resource to extract.</param>
/// <param name="wasCompressed">Resource was compressed in the volume, so it was decompressed.</param>
/// <returns>Binary data for the resource. This is always uncompressed. If the data is compressed in the volume, the volume decoder must decompress it.</returns>
byte[] IVolumeDecoder.ExtractResource(IGameContainer container, string fileName, VolumeResourceMapEntry dirEntry, out bool wasCompressed)
{
if (container == null)
{
throw new ArgumentNullException(nameof(container));
}
if (fileName == null)
{
throw new ArgumentNullException(nameof(fileName));
}
if (fileName.Length == 0)
{
throw new ArgumentException(Errors.FilePathEmpty, nameof(fileName));
}
if (dirEntry == null)
{
throw new ArgumentNullException(nameof(dirEntry));
}
byte[] volumeData = container.Read(fileName);
if (dirEntry.Offset >= volumeData.Length)
{
throw new VolumeDecoderInvalidResourceOffsetException();
}
return(VolumeDecoderV3.ExtractResource(volumeData, dirEntry.Offset, out wasCompressed));
}
