}; // class GifCodeHelper
// Decompress the bytes corresponding to a GIF image.
private static void Decompress
(Stream stream, byte[] buffer, Frame frame, bool interlaced)
{
int minCodeSize, code;
int clearCode, endCode;
int nextCode, oldCode;
GifCodeHelper helper;
ushort[] prefix = new ushort [4096];
byte[] suffix = new byte [4096];
ushort[] length = new ushort [4096];
int offset, x, y, width, height;
int stride, lineChange, temp;
byte[] data;
byte[] stringbuf = new byte [4096];
int stringLen, tempCode, pass;
byte lastSuffix;
// Read the minimum code size and validate it.
if (stream.Read(buffer, 0, 1) != 1)
{
throw new FormatException();
}
minCodeSize = buffer[0];
if (minCodeSize < 2)
{
minCodeSize = 2;
}
else if (minCodeSize > 11)
{
minCodeSize = 11;
}
// Create a code helper.
helper = new GifCodeHelper(stream, buffer, minCodeSize + 1);
// Set the clear and end codes.
clearCode = (1 << minCodeSize);
endCode = clearCode + 1;
nextCode = endCode;
// Initialize the table.
for (code = 0; code < clearCode; ++code)
{
prefix[code] = (ushort)49428;
suffix[code] = (byte)code;
length[code] = (ushort)1;
}
// Initialize the image output parameters.
x = 0;
y = 0;
width = frame.Width;
height = frame.Height;
data = frame.Data;
pass = 0;
lineChange = (interlaced ? 8 : 1);
stride = frame.Stride;
// Process the codes in the input stream.
code = clearCode;
for (;;)
{
oldCode = code;
if ((code = helper.GetCode()) == -1)
{
// We've run out of data blocks.
break;
}
else if (code == clearCode)
{
// Clear the code table and restart.
helper.ResetCodeSize();
nextCode = endCode;
continue;
}
else if (code == endCode)
{
// End of the GIF input stream: skip remaining blocks.
SkipSubBlocks(stream, buffer);
break;
}
else
{
// Sanity check for out of range codes.
if (code > nextCode && nextCode != 0)
{
code = 0;
}
// Update the next code in the table.
prefix[nextCode] = (ushort)oldCode;
length[nextCode] = (ushort)(length[oldCode] + 1);
// Form the full string for this code.
stringLen = length[code];
tempCode = code;
do
{
lastSuffix = suffix[tempCode];
--stringLen;
stringbuf[stringLen] = lastSuffix;
tempCode = prefix[tempCode];
}while(stringLen > 0);
suffix[nextCode] = lastSuffix;
stringLen = length[code];
if (code == nextCode)
{
stringbuf[stringLen - 1] = lastSuffix;
}
// Copy the string into the actual image.
offset = 0;
while (stringLen > 0)
{
temp = width - x;
if (temp > stringLen)
{
temp = stringLen;
}
Array.Copy(stringbuf, offset, data,
y * stride + x, temp);
x += temp;
offset += temp;
stringLen -= temp;
if (x >= width)
{
x = 0;
y += lineChange;
while (y >= height && interlaced)
{
// Move on to the next interlace pass.
++pass;
if (pass == 1)
{
y = 4;
lineChange = 8;
}
else if (pass == 2)
{
y = 2;
lineChange = 4;
}
else if (pass == 3)
{
y = 1;
lineChange = 2;
}
else
{
break;
}
}
if (y >= height)
{
// Shouldn't happen - just in case.
y = 0;
}
}
}
// Set the suffix for the next code.
suffix[nextCode] = (byte)lastSuffix;
// Move on to the next code.
if (nextCode != clearCode)
{
++nextCode;
if (nextCode == helper.codeMax)
{
helper.IncreaseCodeSize();
if (helper.codeSize > 12)
{
helper.ResetCodeSize();
nextCode = clearCode;
}
}
}
}
}
}
}; // class GifCodeHelper
// Decompress the bytes corresponding to a GIF image.
private static void Decompress
(Stream stream, byte[] buffer, Frame frame, bool interlaced)
{
int minCodeSize, code;
int clearCode, endCode;
int nextCode, oldCode;
GifCodeHelper helper;
ushort[] prefix = new ushort [4096];
byte[] suffix = new byte [4096];
ushort[] length = new ushort [4096];
int offset, x, y, width, height;
int stride, lineChange, temp;
byte[] data;
byte[] stringbuf = new byte [4096];
int stringLen, tempCode, pass;
byte lastSuffix;
// Read the minimum code size and validate it.
if(stream.Read(buffer, 0, 1) != 1)
{
throw new FormatException();
}
minCodeSize = buffer[0];
if(minCodeSize < 2)
{
minCodeSize = 2;
}
else if(minCodeSize > 11)
{
minCodeSize = 11;
}
// Create a code helper.
helper = new GifCodeHelper(stream, buffer, minCodeSize + 1);
// Set the clear and end codes.
clearCode = (1 << minCodeSize);
endCode = clearCode + 1;
nextCode = endCode;
// Initialize the table.
for(code = 0; code < clearCode; ++code)
{
prefix[code] = (ushort)49428;
suffix[code] = (byte)code;
length[code] = (ushort)1;
}
// Initialize the image output parameters.
x = 0;
y = 0;
width = frame.Width;
height = frame.Height;
data = frame.Data;
pass = 0;
lineChange = (interlaced ? 8 : 1);
stride = frame.Stride;
// Process the codes in the input stream.
code = clearCode;
for(;;)
{
oldCode = code;
if((code = helper.GetCode()) == -1)
{
// We've run out of data blocks.
break;
}
else if(code == clearCode)
{
// Clear the code table and restart.
helper.ResetCodeSize();
nextCode = endCode;
continue;
}
else if(code == endCode)
{
// End of the GIF input stream: skip remaining blocks.
SkipSubBlocks(stream, buffer);
break;
}
else
{
// Sanity check for out of range codes.
if(code > nextCode && nextCode != 0)
{
code = 0;
}
// Update the next code in the table.
prefix[nextCode] = (ushort)oldCode;
length[nextCode] = (ushort)(length[oldCode] + 1);
// Form the full string for this code.
stringLen = length[code];
tempCode = code;
do
{
lastSuffix = suffix[tempCode];
--stringLen;
stringbuf[stringLen] = lastSuffix;
tempCode = prefix[tempCode];
}
while(stringLen > 0);
suffix[nextCode] = lastSuffix;
stringLen = length[code];
if(code == nextCode)
{
stringbuf[stringLen - 1] = lastSuffix;
}
// Copy the string into the actual image.
offset = 0;
while(stringLen > 0)
{
temp = width - x;
if(temp > stringLen)
{
temp = stringLen;
}
Array.Copy(stringbuf, offset, data,
y * stride + x, temp);
x += temp;
offset += temp;
stringLen -= temp;
if(x >= width)
{
x = 0;
y += lineChange;
while(y >= height && interlaced)
{
// Move on to the next interlace pass.
++pass;
if(pass == 1)
{
y = 4;
lineChange = 8;
}
else if(pass == 2)
{
y = 2;
lineChange = 4;
}
else if(pass == 3)
{
y = 1;
lineChange = 2;
}
else
{
break;
}
}
if(y >= height)
{
// Shouldn't happen - just in case.
y = 0;
}
}
}
// Set the suffix for the next code.
suffix[nextCode] = (byte)lastSuffix;
// Move on to the next code.
if(nextCode != clearCode)
{
++nextCode;
if(nextCode == helper.codeMax)
{
helper.IncreaseCodeSize();
if(helper.codeSize > 12)
{
helper.ResetCodeSize();
nextCode = clearCode;
}
}
}
}
}
}
