private static void CompressDxt5Block(byte[] data, int offset, int width, System.IO.Stream output)
{
int r1 = 255, g1 = 255, b1 = 255, a1 = 255;
int r2 = 0, g2 = 0, b2 = 0, a2 = 0;
//determine the two colors to interpolate between:
//color 1 represents lowest luma, color 2 represents highest luma
for (int i = 0; i < 16; i++)
{
int pixelOffset = offset + (4 * ((i % 4) + (width * (i >> 2))));
int r, g, b, a;
r = data[pixelOffset + 0];
g = data[pixelOffset + 1];
b = data[pixelOffset + 2];
a = data[pixelOffset + 3];
if (r * 299 + g * 587 + b * 114 < r1 * 299 + g1 * 587 + b1 * 114)
{
r1 = r; g1 = g; b1 = b;
}
if (r * 299 + g * 587 + b * 114 > r2 * 299 + g2 * 587 + b2 * 114)
{
r2 = r; g2 = g; b2 = b;
}
if (a < a1)
{
a1 = a;
}
if (a > a2)
{
a2 = a;
}
}
//convert the colors to rgb565 (16-bit rgb)
int r1_565 = (r1 * 0x1f) / 0xff; if (r1_565 > 0x1f)
{
r1_565 = 0x1f;
}
int g1_565 = (g1 * 0x3f) / 0xff; if (g1_565 > 0x3f)
{
g1_565 = 0x3f;
}
int b1_565 = (b1 * 0x1f) / 0xff; if (b1_565 > 0x1f)
{
b1_565 = 0x1f;
}
int r2_565 = (r2 * 0x1f) / 0xff; if (r2_565 > 0x1f)
{
r2_565 = 0x1f;
}
int g2_565 = (g2 * 0x3f) / 0xff; if (g2_565 > 0x3f)
{
g2_565 = 0x3f;
}
int b2_565 = (b2 * 0x1f) / 0xff; if (b2_565 > 0x1f)
{
b2_565 = 0x1f;
}
//luma is also used to determine which color on the palette
//most closely resembles each pixel to compress, so we
//calculate this here
int y1 = r1 * 299 + g1 * 587 + b1 * 114;
int y2 = r2 * 299 + g2 * 587 + b2 * 114;
byte[] newData = new byte[16];
for (int i = 0; i < 16; i++)
{
int pixelOffset = offset + (4 * ((i % 4) + (width * (i >> 2))));
int r, g, b, a;
r = data[pixelOffset + 0];
g = data[pixelOffset + 1];
b = data[pixelOffset + 2];
a = data[pixelOffset + 3];
if (a1 < a2)
{
a -= a1;
a = (a * 0x7) / (a2 - a1);
if (a > 0x7)
{
a = 0x7;
}
switch (a)
{
case 0:
a = 1;
break;
case 1:
a = 7;
break;
case 2:
a = 6;
break;
case 3:
a = 5;
break;
case 4:
a = 4;
break;
case 5:
a = 3;
break;
case 6:
a = 2;
break;
case 7:
a = 0;
break;
}
}
else
{
a = 0;
}
NetBitWriter.WriteUInt32((uint)a, 3, newData, 16 + (i * 3));
int y = r * 299 + g * 587 + b * 114;
int max = y2 - y1;
int diffY = y - y1;
int paletteIndex;
if (diffY < max / 4)
{
paletteIndex = 0;
}
else if (diffY < max / 2)
{
paletteIndex = 2;
}
else if (diffY < max * 3 / 4)
{
paletteIndex = 3;
}
else
{
paletteIndex = 1;
}
newData[12 + (i / 4)] |= (byte)(paletteIndex << (2 * (i % 4)));
}
newData[0] = (byte)a2;
newData[1] = (byte)a1;
newData[9] = (byte)((r1_565 << 3) | (g1_565 >> 3));
newData[8] = (byte)((g1_565 << 5) | b1_565);
newData[11] = (byte)((r2_565 << 3) | (g2_565 >> 3));
newData[10] = (byte)((g2_565 << 5) | b2_565);
output.Write(newData, 0, 16);
}
internal static void Write(ref byte[] buf, ref int bitPos, UInt32 val)
{
EnsureBufferSize(ref buf, bitPos + 32);
NetBitWriter.WriteUInt32(val, 32, buf, bitPos);
bitPos += 32;
}
internal static void Write(ref byte[] buf, ref int bitPos, Int16 val)
{
EnsureBufferSize(ref buf, bitPos + 16);
NetBitWriter.WriteUInt16((UInt16)val, 16, buf, bitPos);
bitPos += 16;
}
internal static void Write(ref byte[] buf, ref int bitPos, byte val)
{
EnsureBufferSize(ref buf, bitPos + 8);
NetBitWriter.WriteByte(val, 8, buf, bitPos);
bitPos += 8;
}
internal static void WriteBytes(ref byte[] buf, ref int bitPos, byte[] val, int pos, int length)
{
EnsureBufferSize(ref buf, bitPos + length * 8);
NetBitWriter.WriteBytes(val, pos, length, buf, bitPos);
bitPos += length * 8;
}
internal static void Write(ref byte[] buf, ref int bitPos, Int64 val)
{
EnsureBufferSize(ref buf, bitPos + 64);
NetBitWriter.WriteUInt64((UInt64)val, 64, buf, bitPos);
bitPos += 64;
}
