Silverlight: How to copy region from WriteableBitmap / BitmapImage? - silverlight

Question

I have such code for Bitmap wrapper.
I need to create overload constructor which cut some rectangle from source image and put it inside _wbmp.
Smth similar to public Bitmap(string fileName, Rectangle area).
Please share some solution.
public Bitmap(string fileName)
{
Uri uri = new Uri(fileName, UriKind.RelativeOrAbsolute);
StreamResourceInfo sri = null;
sri = Application.GetResourceStream(uri);
// Create a new WriteableBitmap object and set it to the JPEG stream.
BitmapImage bitmap = new BitmapImage();
bitmap.CreateOptions = BitmapCreateOptions.None;
bitmap.SetSource(sri.Stream);
_wbmp = new WriteableBitmap(bitmap);
}
Thank you

Answer 1

The WritableBitmap object has a Render method that you can use to render a new bitmap after adding some transformation. In your case you could create and new WritableBitmap with the correct new size to set the button-right corner and then add temporary image with your source and translate it to the left to set the upper left corner. Something like this:
public static WriteableBitmap CropBitmap(string fileName, int newTop, int newRight, int newBottom, int newLeft)
{
Uri uri = new Uri(fileName, UriKind.RelativeOrAbsolute);
StreamResourceInfo sri = null;
sri = Application.GetResourceStream(uri);
// Create a new WriteableBitmap object and set it to the JPEG stream.
BitmapImage bitmapImage = new BitmapImage();
bitmapImage.CreateOptions = BitmapCreateOptions.None;
bitmapImage.SetSource(sri.Stream);
//calculate bounding box
int originalWidth = bitmapImage.PixelWidth;
int originalHeight = bitmapImage.PixelHeight;
int newSmallWidth = newRight - newLeft;
int newSmallHeight = newBottom - newTop;
//generate temporary control to render image
Image temporaryImage = new Image { Source = bitmapImage, Width = originalWidth, Height = originalHeight };
//create writeablebitmap
WriteableBitmap wb = new WriteableBitmap(newSmallWidth, newSmallHeight);
wb.Render(temporaryImage, new TranslateTransform { X = -newLeft, Y = -newTop });
wb.Invalidate();
return wb;
}