Saving image in windows 8.1 using stream and bitmap encoder id

Question

Hi
var renderTargetBitmap = new RenderTargetBitmap();
await renderTargetBitmap.Render(myElementTree);
var pixels = await renderTargetBitmap.GetPixelsAsync();
var picker = new FileSavePicker();
// Picker setup
var file = await picker.PickSaveFileAsync();
// File validation
using (var stream = await file.OpenAsync(FileAccessMode.ReadWrite))
var encoder = await
BitmapEncoder.CreateAsync(BitmapEncoder.BmpEncoderId, stream);
encoder.SetPixelData(BitmapPixelFormat.Rgba8, 100, 0, 96, 96,
await renderTargetBitmap.GetPixelsAsync());
await encoder.FlushAsync();
I have already used the code snippet. Could you please tell me how to save UIElement tree by having the stream and bitmap encoder id as input?
Thanks
Satheesh

Answer 1

Here you go. Set up the file picker and call our CaptureElementToFile function. In this case it's passing the page to capture the whole screen:
FileSavePicker picker = new FileSavePicker();
picker.SuggestedStartLocation = PickerLocationId.PicturesLibrary;
picker.SuggestedFileName = "capture.bmp";
picker.FileTypeChoices.Add("Bitmap File",new List<string>() { ".bmp" });
StorageFile file = await picker.PickSaveFileAsync();
CaptureElementToFile(this, file);
And here's CaptureElementToFile. The BitmapEncoder needs to know information about the size and shape of the pixel buffer and it needs to have the pixels as an Array. If you want to encode to a different size you can include a BitmapTransform.
async void CaptureElementToFile(UIElement element, StorageFile file)
RenderTargetBitmap renderTargetBitmap = new RenderTargetBitmap();
await renderTargetBitmap.RenderAsync(element);
IBuffer pixelBuffer = await renderTargetBitmap.GetPixelsAsync();
DisplayInformation dispInfo = DisplayInformation.GetForCurrentView();
using (var stream = await file.OpenAsync(FileAccessMode.ReadWrite))
var encoder = await BitmapEncoder.CreateAsync(BitmapEncoder.BmpEncoderId, stream);
encoder.SetPixelData(BitmapPixelFormat.Rgba8, BitmapAlphaMode.Straight,
(uint)renderTargetBitmap.PixelWidth,
(uint)renderTargetBitmap.PixelHeight,
dispInfo.LogicalDpi,dispInfo.LogicalDpi,
pixelBuffer.ToArray());
await encoder.FlushAsync();
--Rob