WPF InkCanvas：使用DynamicRenderer绘制线条

Question

I'm writing basic graphic editor in WPF using InkCanvas. I've made some custom shapes (inherited from Stroke). When I draw line wen on InkCanvas, I take first and last point and make a line. That works fine, but now I don't like the default "pen stroke" so i decided to rewrite DynamicRenderer to render line in real time.

Problem is, that DynamicRenderer draws line from origin point to every point of stroke and i obviously don't want that, becouse it makes "fan" insted of line.

There is my custom code and I'm looking for solution to draw line from origin point to last point only, if it is possible.

class LineRenderer : DynamicRenderer
{
    private Point firstPoint;
    private Pen pen = new Pen(new SolidColorBrush(Colors.Gray),1);

    public LineRenderer()
    {
        firstPoint = new Point(double.PositiveInfinity, double.PositiveInfinity);
    }

    protected override void OnStylusDown(RawStylusInput rawStylusInput)
    {
        firstPoint = new Point(rawStylusInput.GetStylusPoints().First().ToPoint().X, rawStylusInput.GetStylusPoints().First().ToPoint().Y);
        base.OnStylusDown(rawStylusInput);
    }

    protected override void OnDraw(DrawingContext drawingContext,
                                   StylusPointCollection stylusPoints,
                                   Geometry geometry, Brush fillBrush)
    {
        drawingContext.DrawLine(pen, firstPoint, stylusPoints.First().ToPoint());
    }

    protected override void OnStylusUp(RawStylusInput rawStylusInput)
    {
        firstPoint = new Point(double.PositiveInfinity, double.PositiveInfinity);
        base.OnStylusUp(rawStylusInput);
    }
}

Answer 1

This is very much late. In order to avoid the "fan" while the stroke is being drawn, try this:

protected override void OnDraw(DrawingContext drawingContext,
                               StylusPointCollection stylusPoints,
                               Geometry geometry, Brush fillBrush)
        {
            if (!_isManipulating)
            {
                _isManipulating = true;
                StylusDevice currentStylus = Stylus.CurrentStylusDevice;
                this.Reset(currentStylus, stylusPoints);
            }
            _isManipulating = false;

            var pen = new Pen(brush, 2);
            drawingContext.DrawLine(pen, startPoint,stylusPoints.First().ToPoint());
       }


protected override void OnStylusDown(RawStylusInput rawStylusInput)
        {
            StylusPointCollection y = rawStylusInput.GetStylusPoints();
            startPoint = (Point)y.First();

            // Allocate memory to store the previous point to draw from.
            prevPoint = new Point(double.NegativeInfinity, double.NegativeInfinity);
            base.OnStylusDown(rawStylusInput);
        }

The trick here is to use DynamicRenderer.Reset , which:

Clears rendering on the current stroke and redraws it.

The redraw will reenter the OnDraw method, so _isManipulating provides a simple flag to stop looping.

Answer 2

what i think in your ondraw function your first point is fixed so it always take it as origin so you can try this for continous drawing.

protected override void OnDraw(DrawingContext drawingContext,
                               StylusPointCollection stylusPoints,
                               Geometry geometry, Brush fillBrush)
{
    drawingContext.DrawLine(pen, firstPoint, stylusPoints.First().ToPoint());
firstPoint = stylusPoints.First().ToPoint();
}

it will update your firstpoint if you get same point exception put a check on it ( or you can define anew point name as previous point and initially make it equal to first point and keep it updating in your ondraw method as i did with first point..

and if you want direct line from first point to last point you can called you on draw method after getting last point from onstylusup method ..hope this might help you..