Question

I am trying to write some code that will allow the user to draw on the touch screen.

When using either GestureService or ManipulationStarted/Delta, there’s a “pause” that occurs when the user starts moving their finger – only when the finger is far enough from the point in which it started, only then do you start getting ManipulationDelta events (and like I said, same deal is true for GestureService).

What can I do to avoid this threshold? It really does not work well with drawing code.

Answer 1

Just blogged about it as I have come across similar questions on AppHub Forum.
https://invokeit.wordpress.com/2012/04/27/high-performance-touch-interface-wpdev-wp7dev/

Manipulation Delta and Gesture services are high level touch interfaces. If you want performance, consider using low level interfaces: Touch and an event called TouchReported. I tend to use them mostly (for drawing / position detection) in many of my projects

The event you want to plug in to detech touch is

Touch.FrameReported += Touch_FrameReported;

You can do this in Loaded event. Here’s the implementation of the Touch_FrameReported handler. WorkArea is Canvas in this. I have also used this in conjugation with WritableBitmap

private void Touch_FrameReported(object sender, TouchFrameEventArgs e)
{
    try
    {
        // Determine if finger / mouse is down
        point = e.GetPrimaryTouchPoint(this.workArea);

        if (point.Position.X < 0 || point.Position.Y < 0)
            return;

        if (point.Position.X > this.workArea.Width || point.Position.Y > this.workArea.Height)
            return;

        if (this.lbLetter.SelectedIndex == -1)
            return;

        switch (point.Action)
        {
            case TouchAction.Down:
                draw = true;
                old_point = point;
                goto default;

            case TouchAction.Up:
                draw = false;
                break;

            default:
                Draw();
                break;
        }
    }
    catch
    {
        MessageBox.Show("Application encountered error processing last request.");
    }
}

This works lot better than high level interfaces.