How can I change the way InkCanvas draws? - wpf

Question

I've searched for examples for this, but the ones I've ran across seem to focus on simpler stuff like setting the InkCanvas DefaultDrawingAttributes such as Width, Height, Color etc. Doesn't seem like there's a lot of material for this.
For example, if I hold down the mouse button I can see it drawing lines. What if I want to draw ellipses instead of lines, or draw ellipses around sampled points between the start and end of the line?
I know I can get new points with the StrokeCollected event, but beyond that I have no idea where to go. This guy seemed like he got msdn's code working, but I couldn't do it. I only know how to build the interface using XAML, and there doesn't seem to be a sample either.
edit
Created a StrokeCollection class variable called thisIsNotNice, initialized in the constructor and did this:
private void InkCanvas_StrokeCollected(object sender, InkCanvasStrokeCollectedEventArgs e)
{
myInkCanvas.Strokes = thisIsNotNice;
foreach (StylusPoint p in e.Stroke.StylusPoints)
{
StylusPointCollection spc = new StylusPointCollection();
spc.Add(p);
Stroke s = new Stroke(spc);
s.DrawingAttributes.Height = 3;
s.DrawingAttributes.Width = 3;
thisIsNotNice.Add(s);
}
e.Handled = true;
}
But it doesn't work as it should. The ellipses are drawn, but the lines drawn by the mouse are still there. Also, for some reason, the first time it works as it should, drawing just the ellipses, but afterward it draws both the ellipses and the lines. But, if I do this instead:
private void InkCanvas_StrokeCollected(object sender, InkCanvasStrokeCollectedEventArgs e)
{
myInkCanvas.Strokes = new System.Windows.Ink.StrokeCollection();
e.Handled = true;
}
The lines aren't kept on the screen. So, I don't understand why they aren't being erased in the above code.
If I do this:
private void InkCanvas_StrokeCollected(object sender, InkCanvasStrokeCollectedEventArgs e)
{
foreach (Stroke s in myInkCanvas.Strokes)
System.Diagnostics.Trace.WriteLine(s);
e.Handled = true;
}
I can also see that the canvas contains the line strokes.
While erasing the strokes after they have been added to the collection is far from ideal, it at least does what I want. I could set up the line color to be the same of the background, but then I wouldn't be able to retrieve just the ellipses. I could copy them to a separate collection too, but that's just awful.

Answer 1

It sounds like you want to customize the way strokes appear on your inkCanvas. There are two separate things to consider here:
1) The way they look as the ink flows off the pen, before it is lifted (the DynamicRenderer, who runs on another thread to ensure that ink is always fast, is responsible for this. It sounds like you're happy with your solution to this already.
2) The way the eventual stroke sitting on the canvas looks. To customize this you might try subclassing Stroke, overriding:
protected override void DrawCore(DrawingContext drawingContext, DrawingAttributes drawingAttributes);
Each time you get a strokeCollected (and here's the same horrible thing you were worried about but there you go), you remove the incoming stroke from the canvas and replace it with your custom implementation, stealing the stroke data from the incoming one.
Your implementation of DrawCore would look something like (pseudocode):
foreach(sp in this.StylusPoints)
drawingContext.DrawEllipse(RADIUS, sp.X, sp.Y)
And so as not to get the lines that normally happen you would not call base.DrawCore(context,attributes) at any point.