Shannon
118 lines
4.3 KiB
C#
118 lines
4.3 KiB
C#
using System;
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namespace Umbraco.Core.Media.Exif
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{
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/// <summary>
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/// Represents an entry in the image file directory.
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/// </summary>
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internal struct ImageFileDirectoryEntry
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{
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/// <summary>
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/// The tag that identifies the field.
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/// </summary>
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public ushort Tag;
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/// <summary>
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/// Field type identifier.
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/// </summary>
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public ushort Type;
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/// <summary>
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/// Count of Type.
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/// </summary>
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public uint Count;
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/// <summary>
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/// Field data.
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/// </summary>
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public byte[] Data;
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/// <summary>
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/// Initializes a new instance of the <see cref="ImageFileDirectoryEntry"/> struct.
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/// </summary>
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/// <param name="tag">The tag that identifies the field.</param>
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/// <param name="type">Field type identifier.</param>
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/// <param name="count">Count of Type.</param>
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/// <param name="data">Field data.</param>
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public ImageFileDirectoryEntry(ushort tag, ushort type, uint count, byte[] data)
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{
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Tag = tag;
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Type = type;
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Count = count;
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Data = data;
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}
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/// <summary>
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/// Returns a <see cref="ImageFileDirectoryEntry"/> initialized from the given byte data.
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/// </summary>
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/// <param name="data">The data.</param>
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/// <param name="offset">The offset into <paramref name="data"/>.</param>
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/// <param name="byteOrder">The byte order of <paramref name="data"/>.</param>
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/// <returns>A <see cref="ImageFileDirectoryEntry"/> initialized from the given byte data.</returns>
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public static ImageFileDirectoryEntry FromBytes(byte[] data, uint offset, BitConverterEx.ByteOrder byteOrder)
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{
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// Tag ID
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ushort tag = BitConverterEx.ToUInt16(data, offset, byteOrder, BitConverterEx.SystemByteOrder);
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// Tag Type
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ushort type = BitConverterEx.ToUInt16(data, offset + 2, byteOrder, BitConverterEx.SystemByteOrder);
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// Count of Type
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uint count = BitConverterEx.ToUInt32(data, offset + 4, byteOrder, BitConverterEx.SystemByteOrder);
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// Field value or offset to field data
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byte[] value = new byte[4];
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Array.Copy(data, offset + 8, value, 0, 4);
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// Calculate the bytes we need to read
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uint baselength = GetBaseLength(type);
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uint totallength = count * baselength;
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// If field value does not fit in 4 bytes
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// the value field is an offset to the actual
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// field value
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if (totallength > 4)
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{
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uint dataoffset = BitConverterEx.ToUInt32(value, 0, byteOrder, BitConverterEx.SystemByteOrder);
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value = new byte[totallength];
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Array.Copy(data, dataoffset, value, 0, totallength);
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}
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// Reverse array order if byte orders are different
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if (byteOrder != BitConverterEx.SystemByteOrder)
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{
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for (uint i = 0; i < count; i++)
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{
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byte[] val = new byte[baselength];
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Array.Copy(value, i * baselength, val, 0, baselength);
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Array.Reverse(val);
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Array.Copy(val, 0, value, i * baselength, baselength);
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}
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}
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return new ImageFileDirectoryEntry(tag, type, count, value);
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}
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/// <summary>
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/// Gets the base byte length for the given type.
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/// </summary>
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/// <param name="type">Type identifier.</param>
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private static uint GetBaseLength(ushort type)
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{
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if (type == 1 || type == 6) // BYTE and SBYTE
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return 1;
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else if (type == 2 || type == 7) // ASCII and UNDEFINED
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return 1;
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else if (type == 3 || type == 8) // SHORT and SSHORT
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return 2;
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else if (type == 4 || type == 9) // LONG and SLONG
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return 4;
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else if (type == 5 || type == 10) // RATIONAL (2xLONG) and SRATIONAL (2xSLONG)
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return 8;
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else if (type == 11) // FLOAT
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return 4;
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else if (type == 12) // DOUBLE
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return 8;
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throw new ArgumentException("Unknown type identifier.", "type");
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}
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}
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}
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