static void Preview(HttpContext context, PreviewImageMode mode)
{
int width, height;
string url, filepath;
Ready(context, out width, out height, out filepath);
var rootPath = context.Server.MapPath("~/");
string thumbnailPath = context.Server.MapPath(ThumbnailLocation) + filepath.Substring(rootPath.Length, filepath.Length - rootPath.Length);
thumbnailPath = thumbnailPath + "_" + width + "_" + height + "_" + Enum.GetName(modeType, mode) + ".jpg";
if (File.Exists(thumbnailPath))
{
OutputImage(context, thumbnailPath);
}
else
{
using (var bitmap = LoadFile(filepath))
{
using (var newImage = GenerateThumbnail(bitmap, mode, width, height))
{
OutputImage(context, newImage);
SaveFile(thumbnailPath, newImage);
}
}
}
}
/// <summary>
/// 生成缩略图核心逻辑
/// </summary>
/// <param name="oldImage">源图片</param>
/// <param name="mode">缩放模式</param>
/// <param name="newWidth">宽度</param>
/// <param name="newHeight">高度</param>
/// <returns></returns>
public static Bitmap GenerateThumbnail(Bitmap oldImage, PreviewImageMode mode, int newWidth, int newHeight)
{
if (newWidth <= 0 || newHeight <= 0)
{
throw new ArgumentOutOfRangeException("newWidth 或 newHeight不能小于0");
}
int oldWidth = oldImage.Width, oldHeight = oldImage.Height;
Bitmap newImage = new Bitmap(newWidth, newHeight);
var interpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
switch (mode)
{
case PreviewImageMode.Cut: //裁剪
if (oldWidth * newHeight > oldHeight * newWidth)
{
oldWidth = oldHeight * newWidth / newHeight;
}
else if (oldWidth * newHeight < oldHeight * newWidth)
{
oldHeight = oldWidth * newHeight / newWidth;
}
using (Graphics g = Graphics.FromImage(newImage))
{
g.InterpolationMode = interpolationMode;
g.DrawImage(oldImage, new Rectangle(0, 0, newImage.Width, newImage.Height), new Rectangle((oldImage.Width - oldWidth) / 2, (oldImage.Height - oldHeight) / 2, oldWidth, oldHeight), GraphicsUnit.Pixel);
}
break;
case PreviewImageMode.LeaveWhite: //留白
int w = newWidth, h = newHeight;
if (oldWidth * newHeight > oldHeight * newWidth)
{
h = oldHeight * newWidth / oldWidth;
}
else if (oldWidth * newHeight < oldHeight * newWidth)
{
w = oldWidth * newHeight / oldHeight;
}
using (Graphics g = Graphics.FromImage(newImage))
{
g.InterpolationMode = interpolationMode;
g.FillRectangle(new SolidBrush(LeaveWhiteColor), new Rectangle(0, 0, newImage.Width, newImage.Height));
g.DrawImage(oldImage, new Rectangle((newImage.Width - w) / 2, (newImage.Height - h) / 2, w, h),
new Rectangle(0, 0, oldImage.Width, oldImage.Height),
GraphicsUnit.Pixel);
}
break;
default:
using (Graphics g = Graphics.FromImage(newImage))
{
g.InterpolationMode = interpolationMode;
g.DrawImage(oldImage, new Rectangle(0, 0, newWidth, newHeight));
}
break;
}
return(newImage);
}