/// <summary>
/// 从输入的Image对象，用指定的预置生成缩略图。
/// </summary>
/// <param name="Input">要生成缩略图的Image对象。</param>
/// <param name="Preset">有关缩略图生成过程参数的预置。</param>
/// <param name="OutputStream">生成的缩略图输出到的流。</param>
/// <returns>返回一个用指定编码器保存的图像的流。</returns>
public static void RenderThumbnail(Image Input, ThumbnailPreset Preset, Stream OutputStream)
{
Rectangle CopyRectangle;
Size RanderContainerSize;
Rectangle RenderRectangle;
CalculateSize(Input.Size, Preset.ThumbnailSize, Preset.ThumbnailResizeMode, out CopyRectangle, out RanderContainerSize, out RenderRectangle);
using (Bitmap outbmp = new Bitmap(RanderContainerSize.Width, RanderContainerSize.Height))
{
using (Graphics g = Graphics.FromImage(outbmp))
{
//渲染背景色
g.DrawRectangle(new Pen(Preset.BackgroundColor), new Rectangle(new Point(0, 0), RanderContainerSize));
//渲染缩略图
g.DrawImage(Input, RenderRectangle, CopyRectangle, GraphicsUnit.Pixel);
//还应根据预置渲染水印图案。
}
//创建输出流。
ImageCodecInfo Encoder = GetEncoder(Preset.OutputFormat);
if (Encoder == null)
{
throw new InvalidOperationException("操作无效。无法找到对应格式的编码器。");
}
EncoderParameters encodeParams = new EncoderParameters(Preset.EncoderParams.Count);
for (int i = 0; i < Preset.EncoderParams.Count; i++)
{
encodeParams.Param[i] = Preset.EncoderParams[i];
}
outbmp.Save(OutputStream, Encoder, encodeParams);
}
}
/// <summary>
/// 从输入的流用指定的预置生成缩略图。
/// </summary>
/// <param name="Input">要生成缩略图的图像的流。</param>
/// <param name="Preset">有关缩略图生成过程参数的预置。</param>
/// <param name="OutputStream"></param>
/// <returns>返回一个用指定编码器保存的图像的流。</returns>
/// <exception cref="ArgumentException">流没有包含有效的图像。</exception>
public static void RenderThumbnail(Stream Input, ThumbnailPreset Preset, Stream OutputStream)
{
Image img = Image.FromStream(Input, true, true);
RenderThumbnail(img, Preset, OutputStream);
}