/// <summary>
/// 为图片添加图片水印
/// </summary>
/// <param name="parameters">添加图片水印相关参数体</param>
/// <param name="errorMsg">错误信息</param>
/// <returns>已加水印的图片数据流</returns>
public static MemoryStream DrawImage(ImageWatermarkParameters parameters, out string errorMsg)
{
errorMsg = string.Empty;
try
{
// 参数检查
if (!parameters.CheckAndSetDefault(out errorMsg))
throw new InvalidDataException(errorMsg);
// 为源图片添加图片水印
Bitmap finalImage = AddWatermarkImageForSourceImage(parameters, out errorMsg);
if (finalImage == null && !string.IsNullOrEmpty(errorMsg))
throw new InvalidDataException("生成水印图片失败：" + errorMsg);
// 获取Bitmap的MemoryStream
return GetMemoryStreamFromBitmap(finalImage, parameters.SourceImageFileExtensionName);
}
catch (Exception ex)
{
errorMsg = ex.Message.ToString();
return null;
}
}
/// <summary>
/// 获取源图片和水印图片的数据流
/// </summary>
/// <param name="parameters">参数实例</param>
/// <param name="sourceImageStream">源图片数据流</param>
/// <param name="waterImageStream">水印图片数据流</param>
/// <param name="errorMsg">错误信息</param>
/// <returns>是否获取成功</returns>
private static bool GetSourceAndWatermarkImageStream(ImageWatermarkParameters parameters,
out MemoryStream sourceImageStream, out MemoryStream waterImageStream, out string errorMsg)
{
errorMsg = string.Empty;
// 根据是否设置图片路径来判断如何获取图片数据流，分别获取源图片和水印图片的数据流。
string scErrMsg = string.Empty, wmErrMsg = string.Empty;
sourceImageStream = parameters.SourceImageStream == null ?
GetImageMemoryStream(parameters.SourceImagePath, out scErrMsg) : parameters.SourceImageStream;
waterImageStream = parameters.WatermarkImageStream == null ?
GetImageMemoryStream(parameters.WatermarkImagePath, out wmErrMsg) : parameters.WatermarkImageStream;
if (!string.IsNullOrEmpty(scErrMsg) || !string.IsNullOrEmpty(wmErrMsg))
{
errorMsg = "通过图片路径获取数据流失败：" + scErrMsg + "；" + wmErrMsg;
return false;
}
return true;
}
/// <summary>
/// 为源图片添加图片水印
/// </summary>
/// <param name="parameters">参数集合</param>
/// <param name="errMsg">错误消息</param>
/// <returns>添加完水印的位图对象</returns>
private static Bitmap AddWatermarkImageForSourceImage(ImageWatermarkParameters parameters, out string errMsg)
{
Image sourceImage = null;
Bitmap sourceBitmap = null;
Graphics sourceGraphics = null;
Image watermarkImage = null;
Graphics watermarkGraphics = null;
errMsg = string.Empty;
try
{
// 获取源图片和水印图片的数据流
MemoryStream sourceImageStream, waterImageStream = null;
if (GetSourceAndWatermarkImageStream(parameters, out sourceImageStream, out waterImageStream, out errMsg) == false)
throw new InvalidDataException(errMsg);
sourceImage = Image.FromStream(sourceImageStream as Stream);
// 实例化一个与源图大小一样、分辨率一致的位图对象，并将其载入Graphics对象中，以便后续编辑；
// 需要根据图像的像素格式来判断是否需要重新绘制该图像
sourceBitmap = (IsPixelFormatIndexed(sourceImage.PixelFormat)) ?
RedrawBitmapByImage(sourceImage) :
new Bitmap(sourceImage.Width, sourceImage.Height, sourceImage.PixelFormat);
sourceBitmap.SetResolution(sourceImage.HorizontalResolution, sourceImage.VerticalResolution);
sourceGraphics = Graphics.FromImage(sourceBitmap);
// SmoothingMode：指定是否将平滑处理（消除锯齿）应用于直线、曲线和已填充区域的边缘。
// 成员名称 说明
// AntiAlias 指定消除锯齿的呈现。
// Default 指定不消除锯齿。
// HighQuality 指定高质量、低速度呈现。
// HighSpeed 指定高速度、低质量呈现。
// Invalid 指定一个无效模式。
// None 指定不消除锯齿。
sourceGraphics.SmoothingMode = SmoothingMode.AntiAlias;
// 将源图像Image对象添加到绘图板中
sourceGraphics.DrawImage(sourceImage, new Rectangle(0, 0, sourceImage.Width, sourceImage.Height),
0, 0, sourceImage.Width, sourceImage.Height, GraphicsUnit.Pixel);
//
// 按照源图片的操作方式，需要创建水印图片的Image对象、位图对象，
// 只是需要根据输入参数来调整水印图片在源图片中的位置、显示效果等。
watermarkImage = new Bitmap(waterImageStream);
// 这里尤其注意，生成新位图的时候，载入的是已经添加了源图片作为背景的位图哦！
// 并将设定好分辨率的位图载入到新的Graphics实例中，以进一步绘制水印。
Bitmap watermarkBitmap = new Bitmap(sourceBitmap);
watermarkBitmap.SetResolution(sourceImage.HorizontalResolution, sourceImage.VerticalResolution);
watermarkGraphics = Graphics.FromImage(watermarkBitmap);
// 通过imageAttributes实例来设定水印图片的绘制效果，包括位置和现实效果等
ImageAttributes imageAttributes = GetImageAttributesInstance(parameters.Alpha);
// 获取水印图片的起始位置
int xPosOfWm, yPosOfWm = 0;
GetWatermarkImagePosition(parameters.WmPosition, sourceImage.Width, sourceImage.Height, watermarkImage.Width, watermarkImage.Height, out xPosOfWm, out yPosOfWm);
// 绘制水印图片
watermarkGraphics.DrawImage(watermarkImage, new Rectangle(xPosOfWm, yPosOfWm, watermarkImage.Width, watermarkImage.Height),
0, 0, watermarkImage.Width, watermarkImage.Height, GraphicsUnit.Pixel, imageAttributes);
return watermarkBitmap;
}
catch (Exception e)
{
errMsg = e.Message.ToString();
return null;
}
finally
{
// 释放
if (sourceImage != null)
sourceImage.Dispose();
if (sourceBitmap != null)
sourceBitmap.Dispose();
if (sourceGraphics != null)
sourceGraphics.Dispose();
if (watermarkImage != null)
watermarkImage.Dispose();
if (watermarkGraphics != null)
watermarkGraphics.Dispose();
}
}
