@ -1,39 +1,56 @@
namespace ImageProcessor.Formats // <copyright file="GifDecoderCore.cs" company="James South">
// Copyright © James South and contributors.
// Licensed under the Apache License, Version 2.0.
// </copyright>
namespace ImageProcessor.Formats
{ {
using System ; using System ;
using System.IO ; using System.IO ;
/// <summary>
/// Performs the gif decoding operation.
/// </summary>
internal class GifDecoderCore internal class GifDecoderCore
{ {
/// <summary>
/// <summary>
/// The maximum comment length.
/// The image to decode the information to.
/// </summary>
private Image decodedImage ;
/// <summary>
/// The currently loaded stream.
/// </summary>
/// </summary>
private const int MaxCommentLength = 1 0 2 4 * 8 ;
private const byte ExtensionIntroducer = 0x21 ;
private const byte Terminator = 0 ;
private const byte ImageLabel = 0x2C ;
private const byte EndIntroducer = 0x3B ;
private const byte ApplicationExtensionLabel = 0xFF ;
private const byte CommentLabel = 0xFE ;
private const byte ImageDescriptorLabel = 0x2C ;
private const byte PlainTextLabel = 0x01 ;
private const byte GraphicControlLabel = 0xF9 ;
private Image image ;
private Stream currentStream ; private Stream currentStream ;
/// <summary>
/// The global color table.
/// </summary>
private byte [ ] globalColorTable ; private byte [ ] globalColorTable ;
private byte [ ] currentFrame ;
internal GifLogicalScreenDescriptor LogicalScreenDescriptor { get ; set ; } /// <summary>
/// The current frame.
/// </summary>
private byte [ ] currentFrame ;
internal GifGraphicsControlExtension GraphicsControlExtension { get ; set ; } /// <summary>
/// The logical screen descriptor.
/// </summary>
private GifLogicalScreenDescriptor logicalScreenDescriptor ;
internal byte Quality { get ; set ; } /// <summary>
/// The graphics control extension.
/// </summary>
private GifGraphicsControlExtension graphicsControlExtension ;
/// <summary>
/// Decodes the stream to the image.
/// </summary>
/// <param name="image">The image to decode to.</param>
/// <param name="stream">The stream containing image data. </param>
public void Decode ( Image image , Stream stream ) public void Decode ( Image image , Stream stream )
{ {
this . image = image ; this . decodedI mage= image ;
this . currentStream = stream ; this . currentStream = stream ;
@ -41,42 +58,42 @@
this . currentStream . Seek ( 6 , SeekOrigin . Current ) ; this . currentStream . Seek ( 6 , SeekOrigin . Current ) ;
this . ReadLogicalScreenDescriptor ( ) ; this . ReadLogicalScreenDescriptor ( ) ;
if ( this . L ogicalScreenDescriptor. GlobalColorTableFlag ) if ( this . l ogicalScreenDescriptor. GlobalColorTableFlag )
{ {
this . globalColorTable = new byte [ this . L ogicalScreenDescriptor. GlobalColorTableSize * 3 ] ; this . globalColorTable = new byte [ this . l ogicalScreenDescriptor. GlobalColorTableSize * 3 ] ;
// Read the global color table from the stream
// Read the global color table from the stream
stream . Read ( this . globalColorTable , 0 , this . globalColorTable . Length ) ; stream . Read ( this . globalColorTable , 0 , this . globalColorTable . Length ) ;
} }
// Loop though the respective gif parts and read the data.
int nextFlag = stream . ReadByte ( ) ; int nextFlag = stream . ReadByte ( ) ;
while ( nextFlag ! = Terminator ) while ( nextFlag ! = GifConstants . Terminator )
{ {
if ( nextFlag = = ImageLabel ) if ( nextFlag = = GifConstants . ImageLabel )
{ {
this . ReadFrame ( ) ; this . ReadFrame ( ) ;
} }
else if ( nextFlag = = ExtensionIntroducer ) else if ( nextFlag = = GifConstants . ExtensionIntroducer )
{ {
int label = stream . ReadByte ( ) ; int label = stream . ReadByte ( ) ;
switch ( label ) switch ( label )
{ {
case GraphicControlLabel : case GifConstants . G raphicControlLabel :
this . ReadGraphicalControlExtension ( ) ; this . ReadGraphicalControlExtension ( ) ;
break ; break ;
case CommentLabel : case GifConstants . CommentLabel :
this . ReadComments ( ) ; this . ReadComments ( ) ;
break ; break ;
case ApplicationExtensionLabel : case GifConstants . ApplicationExtensionLabel :
// TODO: Read Application extension
this . Skip ( 1 2 ) ; // No need to read.
this . Skip ( 1 2 ) ;
break ; break ;
case PlainTextLabel : case GifConstants . PlainTextLabel :
this . Skip ( 1 3 ) ; this . Skip ( 1 3 ) ; // Not supported by any known decoder.
break ; break ;
} }
} }
else if ( nextFlag = = EndIntroducer ) else if ( nextFlag = = GifConstants . EndIntroducer )
{ {
break ; break ;
} }
@ -85,6 +102,9 @@
} }
} }
/// <summary>
/// Reads the graphic control extension.
/// </summary>
private void ReadGraphicalControlExtension ( ) private void ReadGraphicalControlExtension ( )
{ {
byte [ ] buffer = new byte [ 6 ] ; byte [ ] buffer = new byte [ 6 ] ;
@ -93,7 +113,7 @@
byte packed = buffer [ 1 ] ; byte packed = buffer [ 1 ] ;
this . G raphicsControlExtension= new GifGraphicsControlExtension this . g raphicsControlExtension= new GifGraphicsControlExtension
{ {
DelayTime = BitConverter . ToInt16 ( buffer , 2 ) , DelayTime = BitConverter . ToInt16 ( buffer , 2 ) ,
TransparencyIndex = buffer [ 4 ] , TransparencyIndex = buffer [ 4 ] ,
@ -102,12 +122,10 @@
} ; } ;
} }
private void ReadApplicationBlockExtension ( ) /// <summary>
{ /// Reads the image descriptor
// TODO: Implement
/// </summary>
throw new NotImplementedException ( ) ; /// <returns><see cref="GifImageDescriptor"/></returns>
}
private GifImageDescriptor ReadImageDescriptor ( ) private GifImageDescriptor ReadImageDescriptor ( )
{ {
byte [ ] buffer = new byte [ 9 ] ; byte [ ] buffer = new byte [ 9 ] ;
@ -130,6 +148,9 @@
return imageDescriptor ; return imageDescriptor ;
} }
/// <summary>
/// Reads the logical screen descriptor.
/// </summary>
private void ReadLogicalScreenDescriptor ( ) private void ReadLogicalScreenDescriptor ( )
{ {
byte [ ] buffer = new byte [ 7 ] ; byte [ ] buffer = new byte [ 7 ] ;
@ -138,7 +159,7 @@
byte packed = buffer [ 4 ] ; byte packed = buffer [ 4 ] ;
this . L ogicalScreenDescriptor= new GifLogicalScreenDescriptor this . l ogicalScreenDescriptor= new GifLogicalScreenDescriptor
{ {
Width = BitConverter . ToInt16 ( buffer , 0 ) , Width = BitConverter . ToInt16 ( buffer , 0 ) ,
Height = BitConverter . ToInt16 ( buffer , 2 ) , Height = BitConverter . ToInt16 ( buffer , 2 ) ,
@ -148,19 +169,23 @@
GlobalColorTableSize = 2 < < ( packed & 0x07 ) GlobalColorTableSize = 2 < < ( packed & 0x07 )
} ; } ;
if ( this . L ogicalScreenDescriptor. GlobalColorTableSize > 2 5 5 * 4 ) if ( this . l ogicalScreenDescriptor. GlobalColorTableSize > 2 5 5 * 4 )
{ {
throw new ImageFormatException ( throw new ImageFormatException (
$"Invalid gif colormap size '{this.L ogicalScreenDescriptor.GlobalColorTableSize}'" ) ; $"Invalid gif colormap size '{this.l ogicalScreenDescriptor.GlobalColorTableSize}'" ) ;
} }
if ( this . L ogicalScreenDescriptor. Width > ImageBase . MaxWidth | | this . L ogicalScreenDescriptor. Height > ImageBase . MaxHeight ) if ( this . l ogicalScreenDescriptor. Width > ImageBase . MaxWidth | | this . l ogicalScreenDescriptor. Height > ImageBase . MaxHeight )
{ {
throw new ArgumentOutOfRangeException ( throw new ArgumentOutOfRangeException (
$"The input gif '{this.LogicalScreenDescriptor.Width}x{this.L ogicalScreenDescriptor.Height}' is bigger then the max allowed size '{ImageBase.MaxWidth}x{ImageBase.MaxHeight}'" ) ; $"The input gif '{this.logicalScreenDescriptor.Width}x{this.l ogicalScreenDescriptor.Height}' is bigger then the max allowed size '{ImageBase.MaxWidth}x{ImageBase.MaxHeight}'" ) ;
} }
} }
/// <summary>
/// Skips the designated number of bytes in the stream.
/// </summary>
/// <param name="length">The number of bytes to skip.</param>
private void Skip ( int length ) private void Skip ( int length )
{ {
this . currentStream . Seek ( length , SeekOrigin . Current ) ; this . currentStream . Seek ( length , SeekOrigin . Current ) ;
@ -173,25 +198,31 @@
} }
} }
/// <summary>
/// Reads the gif comments.
/// </summary>
private void ReadComments ( ) private void ReadComments ( )
{ {
int flag ; int flag ;
while ( ( flag = this . currentStream . ReadByte ( ) ) ! = 0 ) while ( ( flag = this . currentStream . ReadByte ( ) ) ! = 0 )
{ {
if ( flag > MaxCommentLength ) if ( flag > GifConstants . MaxCommentLength )
{ {
throw new ImageFormatException ( $"Gif comment length '{flag}' exceeds max '{MaxCommentLength}'" ) ; throw new ImageFormatException ( $"Gif comment length '{flag}' exceeds max '{GifConstants. MaxCommentLength}'" ) ;
} }
byte [ ] buffer = new byte [ flag ] ; byte [ ] buffer = new byte [ flag ] ;
this . currentStream . Read ( buffer , 0 , flag ) ; this . currentStream . Read ( buffer , 0 , flag ) ;
this . i mage. Properties . Add ( new ImageProperty ( "Comments" , BitConverter . ToString ( buffer ) ) ) ; this . decodedI mage. Properties . Add ( new ImageProperty ( "Comments" , BitConverter . ToString ( buffer ) ) ) ;
} }
} }
/// <summary>
/// Reads an individual gif frame.
/// </summary>
private void ReadFrame ( ) private void ReadFrame ( )
{ {
GifImageDescriptor imageDescriptor = this . ReadImageDescriptor ( ) ; GifImageDescriptor imageDescriptor = this . ReadImageDescriptor ( ) ;
@ -210,6 +241,11 @@
this . Skip ( 0 ) ; this . Skip ( 0 ) ;
} }
/// <summary>
/// Reads the frame indices marking the color to use for each pixel.
/// </summary>
/// <param name="imageDescriptor">The <see cref="GifImageDescriptor"/>.</param>
/// <returns>The <see cref="T:byte[]"/></returns>
private byte [ ] ReadFrameIndices ( GifImageDescriptor imageDescriptor ) private byte [ ] ReadFrameIndices ( GifImageDescriptor imageDescriptor )
{ {
int dataSize = this . currentStream . ReadByte ( ) ; int dataSize = this . currentStream . ReadByte ( ) ;
@ -220,6 +256,11 @@
return indices ; return indices ;
} }
/// <summary>
/// Reads the local color table from the current frame.
/// </summary>
/// <param name="imageDescriptor">The <see cref="GifImageDescriptor"/>.</param>
/// <returns>The <see cref="T:byte[]"/></returns>
private byte [ ] ReadFrameLocalColorTable ( GifImageDescriptor imageDescriptor ) private byte [ ] ReadFrameLocalColorTable ( GifImageDescriptor imageDescriptor )
{ {
byte [ ] localColorTable = null ; byte [ ] localColorTable = null ;
@ -234,10 +275,16 @@
return localColorTable ; return localColorTable ;
} }
/// <summary>
/// Reads the frames colors, mapping indices to colors.
/// </summary>
/// <param name="indices">The indexed pixels.</param>
/// <param name="colorTable">The color table containing the available colors.</param>
/// <param name="descriptor">The <see cref="GifImageDescriptor"/></param>
private void ReadFrameColors ( byte [ ] indices , byte [ ] colorTable , GifImageDescriptor descriptor ) private void ReadFrameColors ( byte [ ] indices , byte [ ] colorTable , GifImageDescriptor descriptor )
{ {
int imageWidth = this . LogicalScreenDescriptor . Width ; int imageWidth = this . l ogicalScreenDescriptor. Width ;
int imageHeight = this . LogicalScreenDescriptor . Height ; int imageHeight = this . l ogicalScreenDescriptor. Height ;
if ( this . currentFrame = = null ) if ( this . currentFrame = = null )
{ {
@ -246,51 +293,50 @@
byte [ ] lastFrame = null ; byte [ ] lastFrame = null ;
if ( this . G raphicsControlExtension! = null & & if ( this . g raphicsControlExtension! = null & &
this . G raphicsControlExtension. DisposalMethod = = DisposalMethod . RestoreToPrevious ) this . g raphicsControlExtension. DisposalMethod = = DisposalMethod . RestoreToPrevious )
{ {
lastFrame = new byte [ imageWidth * imageHeight * 4 ] ; lastFrame = new byte [ imageWidth * imageHeight * 4 ] ;
Array . Copy ( this . currentFrame , lastFrame , lastFrame . Length ) ; Array . Copy ( this . currentFrame , lastFrame , lastFrame . Length ) ;
} }
int offset = 0 , i = 0 , index = - 1 ; int offset , i = 0 ;
int interlacePass = 0 ; // The interlace pass
int iPass = 0 ; // the interlace pass
int interlaceIncrement = 8 ; // The interlacing line increment
int iInc = 8 ; // the interlacing line increment
int interlaceY = 0 ; // The current interlaced line
int iY = 0 ; // the current interlaced line
int writeY = 0 ; // the target y offset to write to
for ( int y = descriptor . Top ; y < descriptor . Top + descriptor . Height ; y + + ) for ( int y = descriptor . Top ; y < descriptor . Top + descriptor . Height ; y + + )
{ {
// Check if this image is interlaced.
// Check if this image is interlaced.
int writeY ; // the target y offset to write to
if ( descriptor . InterlaceFlag ) if ( descriptor . InterlaceFlag )
{ {
// If so then we read lines at predetermined offsets.
// If so then we read lines at predetermined offsets.
// When an entire image height worth of offset lines has been read we consider this a pass.
// When an entire image height worth of offset lines has been read we consider this a pass.
// With each pass the number of offset lines changes and the starting line changes.
// With each pass the number of offset lines changes and the starting line changes.
if ( iY > = descriptor . Height ) if ( interlace Y > = descriptor . Height )
{ {
iPass + + ; interlace Pass + + ;
switch ( iPass ) switch ( interlace Pass )
{ {
case 1 : case 1 :
iY = 4 ; interlace Y = 4 ;
break ; break ;
case 2 : case 2 :
iY = 2 ; interlace Y = 2 ;
iInc = 4 ; interlace Increment = 4 ;
break ; break ;
case 3 : case 3 :
iY = 1 ; interlace Y = 1 ;
iInc = 2 ; interlace Increment = 2 ;
break ; break ;
} }
} }
writeY = iY + descriptor . Top ; writeY = interlace Y + descriptor . Top ;
iY + = iInc ; interlace Y + = interlace Increment ;
} }
else else
{ {
@ -299,18 +345,18 @@
for ( int x = descriptor . Left ; x < descriptor . Left + descriptor . Width ; x + + ) for ( int x = descriptor . Left ; x < descriptor . Left + descriptor . Width ; x + + )
{ {
offset = ( writeY * imageWidth ) + x ; offset = ( ( writeY * imageWidth ) + x ) * 4 ;
int index = indices [ i ] ;
index = indices [ i ] ;
if ( this . G raphicsControlExtension= = null | | if ( this . g raphicsControlExtension= = null | |
this . G raphicsControlExtension. TransparencyFlag = = false | | this . g raphicsControlExtension. TransparencyFlag = = false | |
this . G raphicsControlExtension. TransparencyIndex ! = index ) this . g raphicsControlExtension. TransparencyIndex ! = index )
{ {
this . currentFrame [ offset * 4 + 0 ] = colorTable [ index * 3 + 2 ] ; int indexOffset = index * 3 ;
this . currentFrame [ offset * 4 + 1 ] = colorTable [ index * 3 + 1 ] ; this . currentFrame [ offset + 0 ] = colorTable [ indexOffset + 2 ] ;
this . currentFrame [ offset * 4 + 2 ] = colorTable [ index * 3 + 0 ] ; this . currentFrame [ offset + 1 ] = colorTable [ indexOffset + 1 ] ;
this . currentFrame [ offset * 4 + 3 ] = ( byte ) 2 5 5 ; this . currentFrame [ offset + 2 ] = colorTable [ indexOffset + 0 ] ;
this . currentFrame [ offset + 3 ] = 2 5 5 ;
} }
i + + ; i + + ;
@ -323,15 +369,15 @@
ImageBase currentImage ; ImageBase currentImage ;
if ( this . i mage. Pixels = = null ) if ( this . decodedI mage. Pixels = = null )
{ {
currentImage = this . i mage; currentImage = this . decodedI mage;
currentImage . SetPixels ( imageWidth , imageHeight , pixels ) ; currentImage . SetPixels ( imageWidth , imageHeight , pixels ) ;
currentImage . Quality = colorTable . Length / 3 ; currentImage . Quality = colorTable . Length / 3 ;
if ( this . G raphicsControlExtension! = null & & this . G raphicsControlExtension. DelayTime > 0 ) if ( this . g raphicsControlExtension! = null & & this . g raphicsControlExtension. DelayTime > 0 )
{ {
this . i mage. FrameDelay = this . G raphicsControlExtension. DelayTime ; this . decodedI mage. FrameDelay = this . g raphicsControlExtension. DelayTime ;
} }
} }
else else
@ -342,32 +388,32 @@
currentImage . SetPixels ( imageWidth , imageHeight , pixels ) ; currentImage . SetPixels ( imageWidth , imageHeight , pixels ) ;
currentImage . Quality = colorTable . Length / 3 ; currentImage . Quality = colorTable . Length / 3 ;
if ( this . G raphicsControlExtension! = null & & this . G raphicsControlExtension. DelayTime > 0 ) if ( this . g raphicsControlExtension! = null & & this . g raphicsControlExtension. DelayTime > 0 )
{ {
currentImage . FrameDelay = this . G raphicsControlExtension. DelayTime ; currentImage . FrameDelay = this . g raphicsControlExtension. DelayTime ;
} }
this . i mage. Frames . Add ( frame ) ; this . decodedI mage. Frames . Add ( frame ) ;
} }
if ( this . G raphicsControlExtension! = null ) if ( this . g raphicsControlExtension! = null )
{ {
if ( this . G raphicsControlExtension. DisposalMethod = = DisposalMethod . RestoreToBackground ) if ( this . g raphicsControlExtension. DisposalMethod = = DisposalMethod . RestoreToBackground )
{ {
for ( int y = descriptor . Top ; y < descriptor . Top + descriptor . Height ; y + + ) for ( int y = descriptor . Top ; y < descriptor . Top + descriptor . Height ; y + + )
{ {
for ( int x = descriptor . Left ; x < descriptor . Left + descriptor . Width ; x + + ) for ( int x = descriptor . Left ; x < descriptor . Left + descriptor . Width ; x + + )
{ {
offset = ( y * imageWidth ) + x ; offset = ( ( y * imageWidth ) + x ) * 4 ;
this . currentFrame [ offset * 4 + 0 ] = 0 ; this . currentFrame [ offset + 0 ] = 0 ;
this . currentFrame [ offset * 4 + 1 ] = 0 ; this . currentFrame [ offset + 1 ] = 0 ;
this . currentFrame [ offset * 4 + 2 ] = 0 ; this . currentFrame [ offset + 2 ] = 0 ;
this . currentFrame [ offset * 4 + 3 ] = 0 ; this . currentFrame [ offset + 3 ] = 0 ;
} }
} }
} }
else if ( this . G raphicsControlExtension. DisposalMethod = = DisposalMethod . RestoreToPrevious ) else if ( this . g raphicsControlExtension. DisposalMethod = = DisposalMethod . RestoreToPrevious )
{ {
this . currentFrame = lastFrame ; this . currentFrame = lastFrame ;
} }
James Jackson-South
11 years ago