C++ whiteboard

Question

How do you create a whiteboard application using C++.

Answer 1

Hello,

Do you want to write an app like draw with mouse?
If so, we can use a Canvas and use PointerMoved event and PointerPressed event to add mouse points to a line and add this line to canvas' children. There is the xaml file

        <Canvas x:Name="Scenario1OutputRoot" Background="White" Height="300" Width="500" PointerMoved="Scenario1OutputRoot_PointerMoved" PointerPressed="Scenario1OutputRoot_PointerPressed" PointerReleased="Scenario1OutputRoot_PointerReleased"/>

Here the cpp file

	// MainPage.xaml.h
	const int SUPPORTEDCONTACTS = 5;
    const double STROKETHICKNESS = 5;
	public ref class MainPage sealed
	{
	private:

        int numActiveContacts;
		Platform::Collections::Map<int, Windows::Foundation::Point>^ contacts;




// ManiPage.xaml.cpp
double Distance(Point currentContact, Point previousContact)
{
	return std::sqrt(std::pow(currentContact.X - previousContact.X, 2) + std::pow(currentContact.Y - previousContact.Y, 2));
}
void Drawpath::MainPage::Scenario1OutputRoot_PointerMoved(Platform::Object^ sender, Windows::UI::Xaml::Input::PointerRoutedEventArgs^ e)
{
	Windows::UI::Input::PointerPoint^ pt = e->GetCurrentPoint(Scenario1OutputRoot);
	int ptrId = pt->PointerId;

	if (contacts->HasKey(ptrId) )
	{
		Point currentContact = pt->Position;
		Point previousContact = contacts->Lookup(ptrId);
		if (Distance(currentContact, previousContact) > 4)
		{
			Windows::UI::Xaml::Shapes::Line^ l = ref new Windows::UI::Xaml::Shapes::Line();

			l->X1 = previousContact.X;
			l->Y1 = previousContact.Y;
			l->X2 = currentContact.X;
			l->Y2 = currentContact.Y;
			l->StrokeThickness = STROKETHICKNESS;
			l->Stroke = ref new SolidColorBrush(Windows::UI::Colors::Red);
			l->StrokeEndLineCap = PenLineCap::Round;


			contacts->Insert(ptrId,currentContact);
			Scenario1OutputRoot->Children->Append(l);
		}
	}

	e->Handled = true;
}


void Drawpath::MainPage::Scenario1OutputRoot_PointerPressed(Platform::Object^ sender, Windows::UI::Xaml::Input::PointerRoutedEventArgs^ e)
{
	if (numActiveContacts >= SUPPORTEDCONTACTS)
	{
		// cannot support more contacts
		return;
	}
	Windows::UI::Input::PointerPoint^ pt = e->GetCurrentPoint(Scenario1OutputRoot);
	contacts->Insert(pt->PointerId, pt->Position);
	e->Handled= true;
	++numActiveContacts;
}


void Drawpath::MainPage::Scenario1OutputRoot_PointerReleased(Platform::Object^ sender, Windows::UI::Xaml::Input::PointerRoutedEventArgs^ e)
{
	int ptrId = e->GetCurrentPoint((FrameworkElement^)sender)->PointerId;

	if (contacts->HasKey(ptrId))
	{

		contacts->Remove(ptrId);
		--numActiveContacts;
	}
	e->Handled = true;
}

Best regards,
Jesse

---

Jesse Jiang [MSFT]
MSDN Community Support | Feedback to us