C# wpf Bitmap转换成WriteableBitmap（BitmapSource）的方法

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前言

在wpf中我们有时候需要截屏或者获取鼠标标时通常拿到的是Bitmap，如果要作显示，则需要将Bitmap转成wpf控件兼容的图像对象，比如转成BitmapSource在网上已经可以查到实现方法，这里提供一种将Bitmap转成WriteableBitmap的方法。

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一、WriteableBitmap是什么？

WriteableBitmap是一个wpf对象，在命名空间System.Windows.Media.Imaging中，是BitmapSource的子类。如下图所示：

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二、如何实现

1.创建WriteableBitmap

创建一个与Bitmap大小相同，像素格式兼容的WriteableBitmap。
示例如下：

WriteableBitmap wb = new WriteableBitmap(bitmap.Width, bitmap.Height, 0, 0, System.Windows.Media.PixelFormats.Bgra32, null);

2.写入数据

调用Bitmap的LockBits获取其内部的图像数据，通过WritePixels的方式写入WriteableBitmap，这样即完成了转换。
示例如下：

var data = bitmap.LockBits(new System.Drawing.Rectangle(new System.Drawing.Point(0, 0), bitmap.Size), System.Drawing.Imaging.ImageLockMode.ReadOnly, src.PixelFormat);
wb.WritePixels(new Int32Rect(srcRect.X, srcRect.Y, srcRect.Width, srcRect.Height), data.Scan0, data.Height * data.Stride, data.Stride, destinationX, destinationY);
bitmap.UnlockBits(data);

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三、完整代码

//将Bitmap 转换成WriteableBitmap 
public static WriteableBitmap BitmapToWriteableBitmap(System.Drawing.Bitmap src)
{
    var wb = CreateCompatibleWriteableBitmap(src);
    System.Drawing.Imaging.PixelFormat format = src.PixelFormat;
    if (wb == null)
    {
        wb = new WriteableBitmap(src.Width, src.Height, 0, 0, System.Windows.Media.PixelFormats.Bgra32, null);
        format = System.Drawing.Imaging.PixelFormat.Format32bppArgb;
    }
    BitmapCopyToWriteableBitmap(src, wb, new System.Drawing.Rectangle(0, 0, src.Width, src.Height), 0, 0, format);
    return wb;
}
//创建尺寸和格式与Bitmap兼容的WriteableBitmap
public static WriteableBitmap CreateCompatibleWriteableBitmap(System.Drawing.Bitmap src)
{
    System.Windows.Media.PixelFormat format;            
    switch (src.PixelFormat)
    {
        case System.Drawing.Imaging.PixelFormat.Format16bppRgb555:
            format = System.Windows.Media.PixelFormats.Bgr555;
            break;
        case System.Drawing.Imaging.PixelFormat.Format16bppRgb565:
            format = System.Windows.Media.PixelFormats.Bgr565;
            break;
        case System.Drawing.Imaging.PixelFormat.Format24bppRgb:
            format = System.Windows.Media.PixelFormats.Bgr24;
            break;
        case System.Drawing.Imaging.PixelFormat.Format32bppRgb:
            format = System.Windows.Media.PixelFormats.Bgr32;
            break;           
        case System.Drawing.Imaging.PixelFormat.Format32bppPArgb:
            format = System.Windows.Media.PixelFormats.Pbgra32;
            break;            
        case System.Drawing.Imaging.PixelFormat.Format32bppArgb:
            format = System.Windows.Media.PixelFormats.Bgra32;
            break;
        default:
            return null;
    }
    return new WriteableBitmap(src.Width, src.Height, 0, 0, format, null);
}
//将Bitmap数据写入WriteableBitmap中
public static void BitmapCopyToWriteableBitmap(System.Drawing.Bitmap src, WriteableBitmap dst, System.Drawing.Rectangle srcRect, int destinationX, int destinationY, System.Drawing.Imaging.PixelFormat srcPixelFormat)
{
    var data = src.LockBits(new System.Drawing.Rectangle(new System.Drawing.Point(0, 0), src.Size), System.Drawing.Imaging.ImageLockMode.ReadOnly, srcPixelFormat);
    dst.WritePixels(new Int32Rect(srcRect.X, srcRect.Y, srcRect.Width, srcRect.Height), data.Scan0, data.Height * data.Stride, data.Stride, destinationX, destinationY);
    src.UnlockBits(data);
}

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四、使用示例

1.直接转换

//创建一个Bitmap对象
var bitmap = new System.Drawing.Bitmap(width, height, System.Drawing.Imaging.PixelFormat.Format32bppArgb);
//绘制Bitmap
//略
//绘制Bitmap--end
//将Bitmap转换为WriteableBitmap
var wb=BitmapToWriteableBitmap(bitmap);

2.复用写入

//创建一个Bitmap对象
var bitmap = new System.Drawing.Bitmap(width, height, System.Drawing.Imaging.PixelFormat.Format32bppArgb);
//创建格式兼容的WriteableBitmap
var wb = CreateCompatibleWriteableBitmap(bitmap);
System.Drawing.Imaging.PixelFormat format = bitmap .PixelFormat;
if (wb == null)
//格式不兼容则强制使用bgr32
{
    wb = new WriteableBitmap(bitmap .Width, bitmap .Height, 0, 0, System.Windows.Media.PixelFormats.Bgra32, null);
    format = System.Drawing.Imaging.PixelFormat.Format32bppArgb;
}
while (true)
{
    //绘制Bitmap
    //略
    //绘制Bitmap--end
    //将Bitmap数据写入WriteableBitmap
    BitmapCopyToWriteableBitmap(bitmap, wb, new System.Drawing.Rectangle(0, 0, bitmap.Width, bitmap.Height), 0, 0, format);
}

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总结

以上就是今天要讲的内容，本质上就是对图像数据的直接拷贝，刚好Bitmap有获取内部数据的接口，而WriteableBitmap也刚好有写入数据的接口。这种方法避免了新的句柄产生，不会出现内存泄漏。而且直接的数据拷贝，不需要编解码，性能是非常好的。