Best way to obtain a visual From a canvas?

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I have an InkCanvas where strokes are collected.

StrokeCollection selectedStrokes = ic.GetSelectedStrokes();

to get the selected strokes and the bounds of just those selected strokes.

what is the best method to capture just the visual of those strokes --not the entire canvas--and their bounding rect so as to directly convert them into a bitmap?

Any help or suggestions are appreciated.

The closest I can find is:

C#

Matrix m =
PresentationSource.FromVisual(canvas).CompositionTarget.TransformToDevice;

But this does not give me just the rectangle surrounding the strokes; infact, nothing showed up at all. (It failed).

I am in WPF C# .net 4.0

Edit: I'm trying to avoid using the strokes as an UI element, and stay strictly with the visual.

I also tried:
RectangleGeometry myRectangleGeometry = new RectangleGeometry();
myRectangleGeometry.Rect = inkBounds;

InkCanvas.Clip = myRectangleGeometry;

Which also fails.

Even doing RenderTargetBitmap.Render(InkCanvas) fails!

The articles mentioned only seem to work for UI elements -- is there a way to use strictly what is visually painted on the screen? (I am totally lost at this point).

Posted 26-May-14 18:34pm

awaynemd

Updated 26-May-14 21:51pm

v3

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Sergey Alexandrovich Kryukov 27-May-14 0:51am

"Capture"?! Don't you see that you already have the Visual? :-)
You only need to render it on a bitmap to get a raster image of it.
—SA

awaynemd 27-May-14 1:12am

I only want a small part of the canvas to be rendered as a bitmap?

awaynemd 27-May-14 1:15am

Sorry...need to add, I would like to avoid using UI element and stay strictly with the visual. (Unless I have no choice).

awaynemd 27-May-14 3:39am

bmp.Render(canvas) did not work.

2 solutions

Solution 1

You don't really need to "capture" the Visual, because System.Windows.Controls.InkCanvas is already System.Windows.Media.Visual:
http://msdn.microsoft.com/en-us/library/system.windows.controls.inkcanvas.aspx[^] :-).

If you need the whole canvas area, it's apparently canvas.ActualWidth and canvas.ActualHeight; and the bitmap could be obtained from any UI element using the class System.Windows.Media.Imaging.RenderTargetBitmap designed exactly for this purpose:
http://msdn.microsoft.com/en-us/library/system.windows.media.imaging.rendertargetbitmap%28v=vs.110%29.aspx[^].

In the page referenced above you can see some sample. Instead of drawingVisual shown in the code sample, render your canvas: bmp.Render(canvas).

—SA

Posted 26-May-14 18:48pm

Sergey Alexandrovich Kryukov

Updated 26-May-14 18:50pm

v3

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awaynemd · Accepted Answer · 2014-05-26T23:13:00

Got it! The trick is to have the InkCanvas draw its strokes onto a new visual. Then use the new visual as the source to the RenderTargetBitmap:

Rect recBounds = inkBounds;

DrawingVisual dv = new DrawingVisual();
DrawingContext dc = dv.RenderOpen();
dc.PushTransform(new TranslateTransform(-recBounds.X, -recBounds.Y));

dContext.DrawRectangle(Brushes.Transparent, null, recBounds);
InkCanvas.Strokes.Draw(dc);
dc.Close();

RenderTargetBitmap rtb =
new RenderTargetBitmap((int)recBounds.Width,
(int)recBounds.Height,
96, 96, PixelFormats.Default);
rtb.Render(dv);