如何在 C#/WPF/WinForms 中将 WMF 渲染为 BitMap 时启用抗锯齿？

Question

为什么在执行此操作时线条等不会消除锯齿？

using (var myGraphics = Graphics.FromImage(bitmap))
{
myGraphics.CompositingQuality = CompositingQuality.HighQuality;
myGraphics.SmoothingMode = SmoothingMode.HighQuality;
myGraphics.TextRenderingHint = TextRenderingHint.AntiAliasGridFit;

myGraphics.Clear(backgroundColor);

myGraphics.EnumerateMetafile(m_metafile, new Point(0, 0), m_metafileDelegate);
}

委托函数如下所示：

private bool MetafileCallback(EmfPlusRecordType recordType, int flags, int dataSize, IntPtr data, PlayRecordCallback callbackData)
{
        byte[] dataArray = null;
        if (data != IntPtr.Zero)
        {
            // Copy the unmanaged record to a managed byte buffer 
            // that can be used by PlayRecord.
            dataArray = new byte[dataSize];
            Marshal.Copy(data, dataArray, 0, dataSize);
        }

        m_metafile.PlayRecord(recordType, flags, dataSize, dataArray);

        return true;
}

我是否需要覆盖特定类型的 PlayRecord 才能在此处获得抗锯齿功能？

WMF 来自 AutoCAD，如果有帮助的话。

Answer 1

这在使用 WMF 图元文件的 GDI+ 中是不可能的，但在 EMF Plus 中是可行的。您可以在源代码处转换为 EMF Plus，或者使用记录不完整的 GDI+ 方法（见下文）即时转换。

GDI（不是 GDI+）渲染 WMF 文件时不使用其下的 GDI+ Graphics 对象的任何合成，它只是直接 GDI 调用的枚举。 See this question for more, but all answers say about the same thing.

如果您可以将文件转换为 EMF Plus，这将使用 GDI+ 方法呈现内容，并使用包括抗锯齿在内的 GDI+ 合成。如果您已经在使用 WPF，您还可以考虑导出到 WPF 可以呈现抗锯齿的 XPS。

如果不能在源头转换，可以从C#调用GDI+方法，但不够优雅。您需要有权访问 System.Drawing 类:

使用的本机句柄

[DllImport("gdiplus.dll", SetLastError = true, ExactSpelling = true, CharSet = System.Runtime.InteropServices.CharSet.Unicode)]
internal static extern int GdipConvertToEmfPlus(HandleRef graphics,
                                                HandleRef metafile,
                                                out Boolean conversionSuccess,
                                                EmfType emfType,
                                                [MarshalAsAttribute(UnmanagedType.LPWStr)]
                                                String description,
                                                out IntPtr convertedMetafile);

您可以将其与类似于以下的代码一起使用：

using (var graphics = Graphics.FromImage(bmp))
using (var metafile = Metafile.FromFile(@"drawing.wmf"))
using (var imageAttr = new ImageAttributes())
{
    graphics.SmoothingMode = SmoothingMode.AntiAlias;
    graphics.CompositingQuality = CompositingQuality.HighQuality;
    graphics.TextRenderingHint = TextRenderingHint.AntiAliasGridFit;

    var metafileHandleField = typeof(Metafile).GetField("nativeImage", BindingFlags.Instance | BindingFlags.NonPublic);
    var imageAttributesHandleField = typeof(ImageAttributes).GetField("nativeImageAttributes", BindingFlags.Instance | BindingFlags.NonPublic);
    var graphicsHandleProperty = typeof(Graphics).GetProperty("NativeGraphics", BindingFlags.Instance | BindingFlags.NonPublic);
    var setNativeImage = typeof(Image).GetMethod("SetNativeImage", BindingFlags.Instance | BindingFlags.NonPublic);
    IntPtr mf = (IntPtr)metafileHandleField.GetValue(metafile);
    IntPtr ia = (IntPtr)imageAttributesHandleField.GetValue(imageAttr);
    IntPtr g = (IntPtr)graphicsHandleProperty.GetValue(graphics);

    Boolean isSuccess;
    IntPtr emfPlusHandle;
    var status = GdipConvertToEmfPlus(new HandleRef(graphics, g),
                                      new HandleRef(metafile, mf),
                                      out isSuccess,
                                      EmfType.EmfPlusOnly,
                                      "",
                                      out emfPlusHandle);
    if (status != 0)
    {
        throw new Exception("Can't convert");
    }

    using (var emfPlus = (Metafile)System.Runtime.Serialization.FormatterServices.GetSafeUninitializedObject(typeof(Metafile)))
    {
        setNativeImage.Invoke(emfPlus, new object[] { emfPlusHandle });

        // use EnumerateMetafile on emfPlus as per your example code or save it:
        emfPlus.Save(@"drawing.emf");
    }
}

Here's a working example for LinqPad。它将 WMF 文件 (drawing.wmf) 转换为 EMF Plus 图元文件，并将其显示在结果面板中。

Paint 中的 WMF 文件：

在 Paint 中转换的 EMF+ 文件：

为了完整起见，上述 GdipConvertToEmfPlus 方法是所谓的“flat API" of GDI+. Its original purpose was to serve only the GDI+ C++ classes. The C++ API which uses this method is called Metafile.ConvertToEmfPlus.

方法的一部分

如何在 C#/WPF/WinForms 中将 WMF 渲染为 BitMap 时启用抗锯齿？

How to enable anti-aliasing when rendering WMF to BitMap in C#/WPF/WinForms?

c#

system.drawing

wmf

metafile

.emf