public static byte[] Decompress(
EndianBinaryReader r,
int width,
int height,
GlTextureFormat inputFormat,
long readLength)
{
bool hasAlpha = (inputFormat == GlTextureFormat.ETC1a4);
byte[] pixelData = new byte[readLength * (hasAlpha ? 4 : 8)];
for (int y = 0; y < height; y += 8)
{
for (int x = 0; x < width; x += 8)
{
Etc1.DecodeETC1Tile_(r,
pixelData,
x,
y,
width,
height,
(hasAlpha ? true : false));
}
}
return(pixelData);
}
private static void DecodeETC1Tile_(
EndianBinaryReader reader,
byte[] pixelData,
int x,
int y,
int width,
int height,
bool hasAlpha)
{
for (int by = 0; by < 8; by += 4)
{
for (int bx = 0; bx < 8; bx += 4)
{
var alpha = 0xFFFFFFFFFFFFFFFF;
if (hasAlpha)
{
alpha = reader.ReadUInt64();
}
var block = reader.ReadUInt64();
using BinaryReader decodedReader =
new BinaryReader(new MemoryStream(Etc1.DecodeETC1Block_(block)));
for (int py = 0; py < 4; py++)
{
for (int px = 0; px < 4; px++)
{
if (x + bx + px >= width)
{
continue;
}
if (y + @by + py >= height)
{
continue;
}
int pixelOffset =
(int)((((y + @by + py) * width) + (x + bx + px)) * 4);
Buffer.BlockCopy(decodedReader.ReadBytes(3),
0,
pixelData,
pixelOffset,
3);
byte pixelAlpha =
(byte)((alpha >> (((px * 4) + py) * 4)) & 0xF);
pixelData[pixelOffset + 3] =
(byte)((pixelAlpha << 4) | pixelAlpha);
}
}
}
}
}
private static byte[] DecodeETC1Block_(ulong block)
{
byte r1, g1, b1, r2, g2, b2;
byte tableIndex1 = (byte)((block >> 37) & 0x07);
byte tableIndex2 = (byte)((block >> 34) & 0x07);
byte diffBit = (byte)((block >> 33) & 0x01);
byte flipBit = (byte)((block >> 32) & 0x01);
if (diffBit == 0x00)
{
/* Individual mode */
r1 = (byte)(((block >> 60) & 0x0F) << 4 | (block >> 60) & 0x0F);
g1 = (byte)(((block >> 52) & 0x0F) << 4 | (block >> 52) & 0x0F);
b1 = (byte)(((block >> 44) & 0x0F) << 4 | (block >> 44) & 0x0F);
r2 = (byte)(((block >> 56) & 0x0F) << 4 | (block >> 56) & 0x0F);
g2 = (byte)(((block >> 48) & 0x0F) << 4 | (block >> 48) & 0x0F);
b2 = (byte)(((block >> 40) & 0x0F) << 4 | (block >> 40) & 0x0F);
}
else
{
/* Differential mode */
/* 5bit base values */
byte r1a = (byte)(((block >> 59) & 0x1F));
byte g1a = (byte)(((block >> 51) & 0x1F));
byte b1a = (byte)(((block >> 43) & 0x1F));
/* Subblock 1, 8bit extended */
r1 = (byte)((r1a << 3) | (r1a >> 2));
g1 = (byte)((g1a << 3) | (g1a >> 2));
b1 = (byte)((b1a << 3) | (b1a >> 2));
/* 3bit modifiers */
sbyte dr2 = (sbyte)((block >> 56) & 0x07);
sbyte dg2 = (sbyte)((block >> 48) & 0x07);
sbyte db2 = (sbyte)((block >> 40) & 0x07);
if (dr2 >= 4)
{
dr2 -= 8;
}
if (dg2 >= 4)
{
dg2 -= 8;
}
if (db2 >= 4)
{
db2 -= 8;
}
/* Subblock 2, 8bit extended */
r2 = (byte)((r1a + dr2) << 3 | (r1a + dr2) >> 2);
g2 = (byte)((g1a + dg2) << 3 | (g1a + dg2) >> 2);
b2 = (byte)((b1a + db2) << 3 | (b1a + db2) >> 2);
}
var decodedData = new byte[(4 * 4) * 3];
var decodedPos = 0;
for (int py = 0; py < 4; py++)
{
for (int px = 0; px < 4; px++)
{
int index = (int)(((block >> ((px * 4) + py)) & 0x1) |
((block >> (((px * 4) + py) + 16)) & 0x1) << 1);
if ((flipBit == 0x01 && py < 2) || (flipBit == 0x00 && px < 2))
{
int modifier = Etc1.ETC1_MODIFIER_TABLES_[tableIndex1, index];
Etc1.WriteClampedByte_(decodedData, ref decodedPos, r1 + modifier);
Etc1.WriteClampedByte_(decodedData, ref decodedPos, g1 + modifier);
Etc1.WriteClampedByte_(decodedData, ref decodedPos, b1 + modifier);
}
else
{
int modifier = Etc1.ETC1_MODIFIER_TABLES_[tableIndex2, index];
Etc1.WriteClampedByte_(decodedData, ref decodedPos, r2 + modifier);
Etc1.WriteClampedByte_(decodedData, ref decodedPos, g2 + modifier);
Etc1.WriteClampedByte_(decodedData, ref decodedPos, b2 + modifier);
}
}
}
return(decodedData);
}