mirror of https://github.com/SixLabors/ImageSharp
Jason Nelson
8 years ago
3 changed files with 90 additions and 62 deletions
@ -1,40 +1,94 @@ |
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// Copyright (c) Six Labors and contributors.
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// Copyright (c) Six Labors and contributors.
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// Licensed under the Apache License, Version 2.0.
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// Licensed under the Apache License, Version 2.0.
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using System; |
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using System.Buffers.Binary; |
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namespace SixLabors.ImageSharp.Formats.Gif |
namespace SixLabors.ImageSharp.Formats.Gif |
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{ |
{ |
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/// <summary>
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/// <summary>
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/// The Graphic Control Extension contains parameters used when
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/// The Graphic Control Extension contains parameters used when
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/// processing a graphic rendering block.
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/// processing a graphic rendering block.
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/// </summary>
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/// </summary>
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internal sealed class GifGraphicsControlExtension |
internal readonly struct GifGraphicsControlExtension |
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{ |
{ |
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public const int Size = 8; |
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public GifGraphicsControlExtension( |
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DisposalMethod disposalMethod, |
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bool transparencyFlag, |
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ushort delayTime, |
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byte transparencyIndex) |
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{ |
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this.DisposalMethod = disposalMethod; |
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this.TransparencyFlag = transparencyFlag; |
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this.DelayTime = delayTime; |
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this.TransparencyIndex = transparencyIndex; |
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} |
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/// <summary>
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/// <summary>
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/// Gets or sets the disposal method which indicates the way in which the
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/// Gets the disposal method which indicates the way in which the
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/// graphic is to be treated after being displayed.
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/// graphic is to be treated after being displayed.
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/// </summary>
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/// </summary>
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public DisposalMethod DisposalMethod { get; set; } |
public DisposalMethod DisposalMethod { get; } |
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/// <summary>
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/// <summary>
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/// Gets or sets a value indicating whether transparency flag is to be set.
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/// Gets a value indicating whether transparency flag is to be set.
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/// This indicates whether a transparency index is given in the Transparent Index field.
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/// This indicates whether a transparency index is given in the Transparent Index field.
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/// (This field is the least significant bit of the byte.)
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/// (This field is the least significant bit of the byte.)
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/// </summary>
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/// </summary>
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public bool TransparencyFlag { get; set; } |
public bool TransparencyFlag { get; } |
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/// <summary>
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/// Gets or sets the transparency index.
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/// The Transparency Index is such that when encountered, the corresponding pixel
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/// of the display device is not modified and processing goes on to the next pixel.
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/// </summary>
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public byte TransparencyIndex { get; set; } |
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/// <summary>
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/// <summary>
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/// Gets or sets the delay time.
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/// Gets the delay time.
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/// If not 0, this field specifies the number of hundredths (1/100) of a second to
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/// If not 0, this field specifies the number of hundredths (1/100) of a second to
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/// wait before continuing with the processing of the Data Stream.
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/// wait before continuing with the processing of the Data Stream.
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/// The clock starts ticking immediately after the graphic is rendered.
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/// The clock starts ticking immediately after the graphic is rendered.
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/// </summary>
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/// </summary>
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public int DelayTime { get; set; } |
public ushort DelayTime { get; } |
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/// <summary>
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/// Gets the transparency index.
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/// The Transparency Index is such that when encountered, the corresponding pixel
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/// of the display device is not modified and processing goes on to the next pixel.
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/// </summary>
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public byte TransparencyIndex { get; } |
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public byte PackField() |
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{ |
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PackedField field = default; |
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field.SetBits(3, 3, (int)this.DisposalMethod); // 1-3 : Reserved, 4-6 : Disposal
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// TODO: Allow this as an option.
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field.SetBit(6, false); // 7 : User input - 0 = none
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field.SetBit(7, this.TransparencyFlag); // 8: Has transparent.
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return field.Byte; |
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} |
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public void WriteTo(Span<byte> buffer) |
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{ |
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buffer[0] = GifConstants.ExtensionIntroducer; |
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buffer[1] = GifConstants.GraphicControlLabel; |
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buffer[2] = 4; // Block Size
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buffer[3] = this.PackField(); // Packed Field
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BinaryPrimitives.WriteUInt16LittleEndian(buffer.Slice(4, 2), this.DelayTime); // Delay Time
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buffer[6] = this.TransparencyIndex; |
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buffer[7] = GifConstants.Terminator; |
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} |
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public static GifGraphicsControlExtension Parse(ReadOnlySpan<byte> buffer) |
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{ |
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// We've already read the Extension Introducer introducer & Graphic Control Label
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// Start from the block size (0)
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byte packed = buffer[1]; |
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return new GifGraphicsControlExtension( |
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disposalMethod: (DisposalMethod)((packed & 0x1C) >> 2), |
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delayTime: BinaryPrimitives.ReadUInt16LittleEndian(buffer.Slice(2, 2)), |
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transparencyIndex: buffer[4], |
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transparencyFlag: (packed & 0x01) == 1); |
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} |
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} |
} |
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} |
} |
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