public virtual void Encode(IRgb24BitmapBase bitmap, Stream stream)
{
if (bitmap == null)
{
throw new ArgumentNullException(nameof(bitmap));
}
if (stream == null)
{
throw new ArgumentNullException(nameof(stream));
}
WriteHeader(stream);
var context = new GifEncodingContext(bitmap, stream);
context.Data = bitmap.GetPixels();
context.Colors = context.Data.Distinct().ToArray();
WriteLogicalScreenDescriptor(context);
// Global color map
WriteColorTable(context);
WriteImageDescriptor(context);
// Local color table: empty
WriteImageData(context);
// Trailer
stream.WriteByte(0x3B);
}
protected void WriteApplicationExtensionBlock(GifEncodingContext context)
{
context.Stream.WriteByte(0x21);
context.Stream.WriteByte(0xFF);
context.Stream.WriteByte(0x0B);
// "NETSCAPE2.0"
context.Stream.WriteByte(0x4E);
context.Stream.WriteByte(0x45);
context.Stream.WriteByte(0x54);
context.Stream.WriteByte(0x53);
context.Stream.WriteByte(0x43);
context.Stream.WriteByte(0x41);
context.Stream.WriteByte(0x50);
context.Stream.WriteByte(0x45);
context.Stream.WriteByte(0x32);
context.Stream.WriteByte(0x2E);
context.Stream.WriteByte(0x30);
context.Stream.WriteByte(0x03);
context.Stream.WriteByte(0x01);
// Loop forever
context.Stream.WriteByte(0x00);
context.Stream.WriteByte(0x00);
context.Stream.WriteByte(0x00);
}
protected void WriteImageData(GifEncodingContext context)
{
int lzwMinCodeSize = context.ColorTableSize + 1;
lzwMinCodeSize = lzwMinCodeSize < 2 ? 2 : lzwMinCodeSize;
// LZW minimum code size
context.Stream.WriteByte((byte)lzwMinCodeSize);
byte[] raster = GetLzwRaster(context.Colors, context.Data, lzwMinCodeSize);
int offset = 0;
while (raster.Length - offset > 255)
{
// Number of bytes in sub-block
context.Stream.WriteByte(255);
// Sub-block
context.Stream.Write(raster, offset, 255);
offset += 255;
}
context.Stream.WriteByte((byte)(raster.Length - offset));
context.Stream.Write(raster, offset, raster.Length - offset);
// Block terminator
context.Stream.WriteByte(0x00);
}
protected void WriteGraphicsControlExtension(GifEncodingContext context)
{
// Extension introducer
context.Stream.WriteByte(0x21);
// Graphic control label
context.Stream.WriteByte(0xF9);
// Block size
context.Stream.WriteByte(0x04);
// Packed field
// Reserved
// Disposal method: 1
// User input flag
// Transparent color flag
context.Stream.WriteByte(0x04);
// Delay time
context.Stream.WriteByte(0x0A);
context.Stream.WriteByte(0x00);
// Transparent color index
context.Stream.WriteByte(0x00);
// Block terminator
context.Stream.WriteByte(0x00);
}
public override void Encode(IRgb24BitmapBase bitmap, Stream stream)
{
if (bitmap == null)
{
throw new ArgumentNullException(nameof(bitmap));
}
if (stream == null)
{
throw new ArgumentNullException(nameof(stream));
}
WriteHeader(stream);
var context = new GifEncodingContext(bitmap, stream);
var bmp = bitmap as IRgb24Bitmap;
if (bmp != null && bmp.FrameCount > 1)
{
context.Colors = Enumerable.Range(0, bmp.FrameCount)
.Select(i => bmp.GetFrame(i).GetPixels())
.SelectMany(l => l)
.Distinct()
.ToArray();
WriteLogicalScreenDescriptor(context);
WriteColorTable(context);
WriteApplicationExtensionBlock(context);
WriteGraphicsControlExtension(context);
for (var i = 0; i < bmp.FrameCount; i++)
{
var frame = bmp.GetFrame(i);
var fContext = new GifEncodingContext(frame, stream);
fContext.Data = frame.GetPixels();
fContext.Colors = context.Colors;
WriteImageDescriptor(fContext);
WriteImageData(fContext);
}
}
else
{
context.Data = bitmap.GetPixels();
context.Colors = context.Data.Distinct().ToArray();
WriteLogicalScreenDescriptor(context);
WriteColorTable(context);
WriteImageDescriptor(context);
WriteImageData(context);
}
// Trailer
stream.WriteByte(0x3B);
}
protected void WriteColorTable(GifEncodingContext context)
{
int colorCount = 1 << (context.ColorTableSize + 1);
int count = 0;
foreach (var color in context.Colors)
{
// RGB24
WriteInt24(context.Stream, color);
count += 1;
}
while (count < colorCount)
{
context.Stream.WriteByte(0);
context.Stream.WriteByte(0);
context.Stream.WriteByte(0);
count += 1;
}
}
protected void WriteImageDescriptor(GifEncodingContext context)
{
// Image separator
context.Stream.WriteByte(0x2C);
// Image left position
WriteInt16(context.Stream, 0);
// Image top position
WriteInt16(context.Stream, 0);
// Image width
WriteInt16(context.Stream, context.Bitmap.Width, true);
// Image height
WriteInt16(context.Stream, context.Bitmap.Height, true);
// Packed field
// Local color table flag
// Interlace flag
// Sort flag
// Reserved
// Size of local color table
context.Stream.WriteByte(0);
}
protected void WriteLogicalScreenDescriptor(GifEncodingContext context)
{
// Canvas width
WriteInt16(context.Stream, context.Bitmap.Width, true);
// Canvas height
WriteInt16(context.Stream, context.Bitmap.Height, true);
context.ColorTableSize = GetGlobalColorTableSize(context.Colors.Length);
// Packed field
// Global color table flag: 1
// Color resolution: 111 (8 bits/pixel)
// Sort flag: 0
// Size of global color table: 2^(N+1)
context.Stream.WriteByte((byte)(0b1_111_0_000 | context.ColorTableSize & 0b111));
// Background color index
context.Stream.WriteByte(0x00);
// Pixel aspect ratio
context.Stream.WriteByte(0x00);
}
