Take a Screenshot programmatically

Question

Hello,

i wonder if it is possible to take a Screenshot from any Device and save it into the Filesystem as Jpeg-StorageFile.

This is what i already have:

RenderTargetBitmap bitmap = new RenderTargetBitmap();
await bitmap.RenderAsync(MyOuterGrid);

IBuffer buffer = await bitmap.GetPixelsAsync();

This is what i have tried:

byte[] bytearray = buffer.ToArray();

Stream stream = buffer.AsStream();
IRandomAccessStream randomaccessstream = stream.AsRandomAccessStream();
randomaccessstream.Seek(0);
            
var encoderId = BitmapEncoder.JpegEncoderId;
var encoder = await BitmapEncoder.CreateAsync(encoderId, randomaccessstream);

//I don't get what this method does
encoder.SetPixelData(BitmapPixelFormat.Rgba8, BitmapAlphaMode.Straight, 10, 15, 64, 64, bytearray);

//Here it stops
await encoder.FlushAsync();

How can i encode the Bitmap to a Jpeg?

Answer 1

encoder.SetPixelData hands over the data the encoder is supposed to encode. In order to do that it needs to know the dimensions of the image (width, height). So right now you tell the encoder that you are providing an image 10 pixels wide and 15 pixels high with a pixel density of 64 dpi.

For correct usage this should read like this:

encoder.SetPixelData(BitmapPixelFormat.Rgba8, BitmapAlphaMode.Straight, (uint)bitmap.Width, (uint)bitmap.Height, 96, 96, bytearray);

Answer 2

Thanks for your explanation. I got it now. 

But it still does lock or freeze the screen at encoder.FlushAsync();

Answer 3

Have you checked the dimensions of the created RenderTargetBitmap? You're not setting the dimensions yourself so perhaps something's wrong there.

If I go by this sample you might also change the BitmapAlphaMode to Ignore: http://basquang.wordpress.com/2013/09/26/windows-store-8-1-save-visual-element-to-bitmap-image-file/

Edit: I now also noticed that you are using the buffer that you are reading the image from as the target for saving it to. This might also be a problem - especially given that this Buffer is still connected to the RenderTargetBitmap.

You might want to first test this with writing everything to a file and then with a newly created Buffer to avoid issues.

Answer 4

Oh ye. Now it works perfectly :) Thanks

Show Case App How-To Take Screenshots