imagedescriptor.cs

gif图像处理 包括对多帧gif动画的缩放

#region Copyright & License
/*-------------------------New BSD License ------------------
 Copyright (c) 2008, jillzhang
All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

* Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

* Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

* Neither the name of jillzhang nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
 */
#endregion

using System;
using System.Collections.Generic;
using System.Text;
using System.IO;

namespace Jillzhang.GifUtility
{
    #region 类ImageDescriptor
    /// <summary>
    /// 图象标识符(Image Descriptor)一个GIF文件内可以包含多幅图象，
    /// 一幅图象结束之后紧接着下是一幅图象的标识符，图象标识符以0x2C(',')
    /// 字符开始，定义紧接着它的图象的性质，包括图象相对于逻辑屏幕边界的偏移量、
    /// 图象大小以及有无局部颜色列表和颜色列表大小，由10个字节组成
    /// </summary>
    internal class ImageDescriptor
    {
        #region 结构字段      

        /// <summary>
        /// X方向偏移量
        /// </summary>
        internal short XOffSet;

        /// <summary>
        /// X方向偏移量
        /// </summary>
        internal short YOffSet;

        /// <summary>
        /// 图象宽度
        /// </summary>
        internal short Width;

        /// <summary>
        /// 图象高度
        /// </summary>
        internal short Height;     

        /// <summary>
        /// packed
        /// </summary>
        internal byte Packed;

        /// <summary>
        /// 局部颜色列表标志(Local Color Table Flag)
        /// 置位时标识紧接在图象标识符之后有一个局部颜色列表，供紧跟在它之后的一幅图象使用；
        /// 值否时使用全局颜色列表，忽略pixel值。
        /// </summary>
        internal bool LctFlag;    

        /// <summary>
        /// 交织标志(Interlace Flag)，置位时图象数据使用连续方式排列，否则使用顺序排列。
        /// </summary>
        internal bool InterlaceFlag;

        /// <summary>
        ///  分类标志(Sort Flag)，如果置位表示紧跟着的局部颜色列表分类排列.
        /// </summary>
        internal bool SortFlag;

        /// <summary>
        ///  pixel - 局部颜色列表大小(Size of Local Color Table)，pixel+1就为颜色列表的位数
        /// </summary>
        internal int LctSize;
        #endregion     

        #region 方法函数
        internal byte[] GetBuffer()
        {
            List<byte> list = new List<byte>();
            list.Add(GifExtensions.ImageDescriptorLabel);
            list.AddRange(BitConverter.GetBytes(XOffSet));
            list.AddRange(BitConverter.GetBytes(YOffSet));
            list.AddRange(BitConverter.GetBytes(Width));
            list.AddRange(BitConverter.GetBytes(Height));
            byte packed = 0;
            int m = 0;
            if (LctFlag)
            {
                m = 1;
            }
            int i = 0;
            if (InterlaceFlag)
            {
                i = 1;
            }
            int s = 0;
            if (SortFlag)
            {
                s = 1;
            }
            byte pixel = (byte)(Math.Log(LctSize,2) - 1);
            packed = (byte)(pixel | (s << 5) | (i << 6) | (m << 7));
            list.Add(packed);          
            return list.ToArray();
        }
        #endregion
    }
    #endregion
}