如何将图片合并成WriteableBitmap？

Question

我有这样的位图：

var map = new WriteableBitmap(800,800,800,800, PixelFormats.Bgr32,null);

然后我有一个50x50PNG图片，我想合并到这个位图(包括透明度)的位置偏移顶部100左150 (从左上角的位图)。

var img = new BitmapImage(new Uri(@"D:\test.png", UriKind.Absolute));

我尝试过类似map.WritePixels(img);之类的东西，但这只会引发一个错误。如何将此图像合并到位图中？

Answer 1

只需将颜色值复制到缓冲区，然后将其复制回WriteableBitmap

public void Chubs_BitBltMerge(ref WriteableBitmap dest, int nXDest, int nYDest, ref BitmapImage src)
{
    // copy the source image into a byte buffer
    int src_stride = src.PixelWidth * (src.Format.BitsPerPixel >> 3);
    byte[] src_buffer = new byte[src_stride * src.PixelHeight];
    src.CopyPixels(src_buffer, src_stride, 0);

    // copy the dest image into a byte buffer
    int dest_stride = src.PixelWidth * (dest.Format.BitsPerPixel >> 3);           
    byte[] dest_buffer = new byte[(src.PixelWidth * src.PixelHeight) << 2];
    dest.CopyPixels(new Int32Rect(nXDest, nYDest, src.PixelWidth, src.PixelHeight), dest_buffer, dest_stride, 0);

    // do merge (could be made faster through parallelization)
    for (int i = 0; i < src_buffer.Length; i = i + 4)
    {
        float src_alpha = ((float)src_buffer[i + 3] / 255);
        dest_buffer[i + 0] = (byte)((src_buffer[i + 0] * src_alpha) + dest_buffer[i + 0] * (1.0 - src_alpha));
        dest_buffer[i + 1] = (byte)((src_buffer[i + 1] * src_alpha) + dest_buffer[i + 1] * (1.0 - src_alpha));
        dest_buffer[i + 2] = (byte)((src_buffer[i + 2] * src_alpha) + dest_buffer[i + 2] * (1.0 - src_alpha));
    }

    // copy dest buffer back to the dest WriteableBitmap
    dest.WritePixels(new Int32Rect(nXDest, nYDest, src.PixelWidth, src.PixelHeight), dest_buffer, dest_stride, 0);
}

public MainWindow()
{
    InitializeComponent();

    BitmapImage texture = new BitmapImage(new Uri("50x50.png", UriKind.Relative));

    Image background = new Image();
    background.Source = new BitmapImage(new Uri("backdrop.png", UriKind.Relative));
    WriteableBitmap wb = new WriteableBitmap((BitmapSource)background.Source);

    // bit the 50x50 onto the backdrop
    Chubs_BitBltMerge(ref wb, 150, 100, ref texture);

    // set the result to an Image in XAML to see the result
    //this.myImage.Source = wb;
    //this.myImage.Width = wb.PixelWidth;
    //this.myImage.Height = wb.PixelHeight;

}

​

​

Answer 2

在计算alpha通道的值时，请确保正在对浮点值进行除法，例如，使用255.0而不是255个，否则当alpha = 255时只得到src_alpha =1，否则只得到src_alpha =0时。虽然变化很小，但在半透明的情况下影响很大。所以我的解决方案是这样的：

    public void Chubs_BitBltMerge(ref WriteableBitmap dest, int nXDest, int nYDest, ref BitmapImage src)
    {
        // copy the source image into a byte buffer
        int src_stride = src.PixelWidth * (src.Format.BitsPerPixel >> 3);
        byte[] src_buffer = new byte[src_stride * src.PixelHeight];
        src.CopyPixels(src_buffer, src_stride, 0);

       // copy the dest image into a byte buffer
       int dest_stride = src.PixelWidth * (dest.Format.BitsPerPixel >> 3);           
       byte[] dest_buffer = new byte[(src.PixelWidth * src.PixelHeight) << 2];
       dest.CopyPixels(new Int32Rect(nXDest, nYDest, src.PixelWidth, src.PixelHeight), dest_buffer, dest_stride, 0);

       // do merge (could be made faster through parallelization)
       for (int i = 0; i < src_buffer.Length; i = i + 4)
       {
           float src_alpha = (float)(src_buffer[i + 3] / 255.0);
           dest_buffer[i + 0] = (byte)((src_buffer[i + 0] * src_alpha) + dest_buffer[i + 0] * (1.0 - src_alpha));
           dest_buffer[i + 1] = (byte)((src_buffer[i + 1] * src_alpha) + dest_buffer[i + 1] * (1.0 - src_alpha));
           dest_buffer[i + 2] = (byte)((src_buffer[i + 2] * src_alpha) + dest_buffer[i + 2] * (1.0 - src_alpha));
       }

       // copy dest buffer back to the dest WriteableBitmap
       dest.WritePixels(new Int32Rect(nXDest, nYDest, src.PixelWidth, src.PixelHeight), dest_buffer, dest_stride, 0);
    }