Following on from that previous post I wanted to take a look at processing raw touch events.
In truth, I suspect that most application developers don’t want raw touch events and would rather work at the level of gestures and/or manipulations but being able to get access to the raw events at least means that you (or someone else) can build a higher level framework so I think it’s worth starting at the bottom of the stack.
Let’s take a look at just picking up some raw events across different frameworks.
Silverlight 4
In Silverlight 4, raw touch events are pretty much all you get in the framework and it’s surfaced in a very simple way. I wrote a little control that displays an arc (from Blend 4’s shapes) and spins it around and called it SpinnyControl and then I authored a UI consisting of only a Black Grid and wrote this tiny bit of code behind for it;
public partial class MainPage : UserControl
{
Dictionary<int, SpinnyControl> controls;
public MainPage()
{
InitializeComponent();
this.controls = new Dictionary<int, SpinnyControl>();
this.Loaded += OnLoaded;
}
void OnLoaded(object sender, RoutedEventArgs e)
{
Touch.FrameReported += OnTouchFrameReported;
}
void OnTouchFrameReported(object sender, TouchFrameEventArgs e)
{
TouchPointCollection points = e.GetTouchPoints(this.LayoutRoot);
foreach (var item in points.Where(p => p.Action == TouchAction.Down))
{
SpinnyControl control = new SpinnyControl()
{
HorizontalAlignment = HorizontalAlignment.Left,
VerticalAlignment = VerticalAlignment.Top
};
this.controls[item.TouchDevice.Id] = control;
this.LayoutRoot.Children.Add(control);
control.RenderTransform = new TranslateTransform()
{
X = item.Position.X - (control.Width / 2),
Y = item.Position.Y - (control.Height) / 2
};
}
foreach (var item in points.Where(p => p.Action == TouchAction.Up))
{
SpinnyControl control = this.controls[item.TouchDevice.Id];
this.LayoutRoot.Children.Remove(control);
}
foreach (var item in points.Where(p => p.Action == TouchAction.Move))
{
SpinnyControl control = this.controls[item.TouchDevice.Id];
((TranslateTransform)control.RenderTransform).X =
item.Position.X - (control.Width / 2);
((TranslateTransform)control.RenderTransform).Y =
item.Position.Y - (control.Height / 2);
}
}
}
and you can see that running here on my touch screen;
and you can try it yourself here if you’ve got a touch screen;
and here’s the source.
WPF
We can get the same raw touch events delivered in WPF so I made a blank WPF 4.0 application and left the UI as a single black Grid with event handlers added to it for the touch events because in WPF touch events are routed to controls whereas in Silverlight I just get the events delivered to the main window and it’s then up to me to figure out which controls that may or may not impact.
<Grid
x:Name="LayoutRoot"
Stylus.IsPressAndHoldEnabled="False"
Background="Black"
TouchDown="OnTouchDown"
TouchUp="OnTouchUp"
TouchMove="OnTouchMove">
</Grid>
There’s also something else pretty important on that Grid definition and that’s the Stylus.IsPressAndHoldEnabled=”False” because without that the OS will try and look for Press+Hold gestures rather than just allow the touch events through to the app.
I also copied over my SpinnyControl user control although, to be honest, I found it easier to re-create the animations quickly in Blend rather than try and remember the property syntax as I changed them from CompositeTransform to TransformGroup.
With that done, the code’s the same as it was but re-org’d to fit with WPF’s eventing scheme;
public partial class MainWindow : Window
{
Dictionary<int, SpinnyControl> controls;
public MainWindow()
{
InitializeComponent();
this.controls = new Dictionary<int, SpinnyControl>();
}
void OnTouchDown(object sender, TouchEventArgs e)
{
TouchPoint point = e.GetTouchPoint(this.LayoutRoot);
SpinnyControl control = new SpinnyControl()
{
HorizontalAlignment = HorizontalAlignment.Left,
VerticalAlignment = VerticalAlignment.Top
};
this.controls[e.TouchDevice.Id] = control;
this.LayoutRoot.Children.Add(control);
control.RenderTransform = new TranslateTransform()
{
X = point.Position.X - (control.Width / 2),
Y = point.Position.Y - (control.Height) / 2
};
e.Handled = true;
}
void OnTouchUp(object sender, TouchEventArgs e)
{
SpinnyControl control = this.controls[e.TouchDevice.Id];
this.LayoutRoot.Children.Remove(control);
e.Handled = true;
}
void OnTouchMove(object sender, TouchEventArgs e)
{
TouchPoint point = e.GetTouchPoint(this.LayoutRoot);
SpinnyControl control = this.controls[e.TouchDevice.Id];
((TranslateTransform)control.RenderTransform).X =
point.Position.X - (control.Width / 2);
((TranslateTransform)control.RenderTransform).Y =
point.Position.Y - (control.Height / 2);
e.Handled = true;
}
}
and you can find that code here and I even changed the colours for WPF 
Silverlight on Windows Phone
What about on the Windows Phone 7? Ideally, I’d just lift my Silverlight 4 code and drop it straight down onto the phone.
I hit a stumbling block because I’d gone and used a shape from the Microsoft.Expression.Drawing.dll and that’s not strictly available on the phone. So, I went back to Blend and converted it into a Path for the phone and used that instead.
Other than that the source code copied straight across from Silverlight on the desktop and just worked – in fact, it took me more time to figure out how the heck to print the screenshot of the device in action because it’s not-so-easy to do if you want to take the screenshot whilst the device actually has the focus (which it will do if you’ve got 2 fingers pressed to the screen 
).
So, all-in-all the raw touch capabilities are all there in a pretty consistent format on each framework and it’s easy enough to at least get going with it.
What about gestures?…
Mike Taulty 