/// <summary>
/// 为图片添加文字水印
/// </summary>
/// <param name="parameters">文字水印过程需要的参数体</param>
/// <param name="errorMsg">异常信息</param>
/// <returns>已加水印的图片数据流</returns>
public static MemoryStream DrawText(TextWatermarkParameters parameters, out string errorMsg)
{
errorMsg = string.Empty;
try
{
// 参数检查
if (!parameters.CheckAndSetDefault(out errorMsg))
throw new InvalidDataException(errorMsg);
// 为源图片添加文字水印
Bitmap finalImage = AddWatermarkTextForSourceImage(parameters, out errorMsg);
if (finalImage == null && !string.IsNullOrEmpty(errorMsg))
throw new InvalidDataException("生成水印图片失败：" + errorMsg);
return GetMemoryStreamFromBitmap(finalImage, parameters.SourceImageFileExtensionName);
}
catch (Exception ex)
{
errorMsg = ex.Message.ToString();
return null;
}
}
/// <summary>
/// 为图片添加文字水印
/// </summary>
/// <param name="parameters">文字水印相关参数体</param>
/// <param name="errMsg">错误信息</param>
/// <returns>添加完水印的位图对象</returns>
private static Bitmap AddWatermarkTextForSourceImage(TextWatermarkParameters parameters, out string errMsg)
{
Image srcImage = null;
Graphics srcGraphics = null;
errMsg = string.Empty;
try
{
//
// 获取源图片数据流
MemoryStream scMs = parameters.SourceImageStream == null ?
GetImageMemoryStream(parameters.SourceImagePath, out errMsg) : parameters.SourceImageStream;
if (scMs == null && !string.IsNullOrEmpty(errMsg))
throw new InvalidDataException("获取图片数据流失败！");
//
//
srcImage = Image.FromStream(scMs as Stream);
// 新建位图并设定分辨率，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
Bitmap srcBitmap = (IsPixelFormatIndexed(srcImage.PixelFormat)) ?
RedrawBitmapByImage(srcImage) :
new Bitmap(srcImage.Width, srcImage.Height, srcImage.PixelFormat);
srcBitmap.SetResolution(srcImage.HorizontalResolution, srcImage.VerticalResolution);
// 封装一个GDI+绘图图面，并设置图形品质
srcGraphics = Graphics.FromImage(srcBitmap);
srcGraphics.SmoothingMode = SmoothingMode.AntiAlias;
// 向源图片绘制到位图中
srcGraphics.DrawImage(srcImage, new Rectangle(0, 0, srcImage.Width, srcImage.Height), 0, 0, srcImage.Width, srcImage.Height, GraphicsUnit.Pixel);
//
// 矩形的宽度和高度，SizeF有三个属性，分别为Height高，width宽，IsEmpty是否为空
SizeF crSize = srcGraphics.MeasureString(parameters.WatermarkText, parameters.WmTextFont);
// 获取水印文字的起始位置
float xPosOfWm, yPosOfWm = 0;
GetWatermarkTextPosition(parameters.WmPosition, srcImage.Width, srcImage.Height, crSize.Width, crSize.Height, out xPosOfWm, out yPosOfWm);
//
// 文本样式
StringFormat vmTextFormat = GetStringFormat();
// 阴影画刷
SolidBrush shadowBrush = GetShadowBrush();
// 文字画刷
SolidBrush semiTransBrush = GetTextBrush(parameters.Alpha);
// 第一步，绘制阴影
srcGraphics.DrawString(parameters.WatermarkText, parameters.WmTextFont, shadowBrush,
new PointF(xPosOfWm + parameters.TextShadowWidth, yPosOfWm + parameters.TextShadowWidth), vmTextFormat);
// 第二步，绘制文字
srcGraphics.DrawString(parameters.WatermarkText, parameters.WmTextFont, semiTransBrush, new PointF(xPosOfWm, yPosOfWm), vmTextFormat);
return srcBitmap;
}
catch (Exception e)
{
errMsg = e.Message.ToString();
return null;
}
finally
{ // 释放资源
if (srcImage != null)
srcImage.Dispose();
if (srcGraphics != null)
srcGraphics.Dispose();
}
}
