WinRT glue for video I/O

Overview

// enums

enum
{
    cv::@105::OPEN_CAMERA          = 300,
    cv::@105::CLOSE_CAMERA,
    cv::@105::UPDATE_IMAGE_ELEMENT,
    cv::@105::SHOW_TRACKBAR,
};

// global functions

void
cv::winrt_imshow();

void
cv::winrt_onVisibilityChanged(bool visible);

void
cv::winrt_setFrameContainer(::Windows::UI::Xaml::Controls::Image^ image);

template <typename ... Args>
void
cv::winrt_startMessageLoop(
    std::function<void(Args...)>&& callback,
    Args... args
    );

template <typename ... Args>
void
cv::winrt_startMessageLoop(
    void  callback Args...,
    Args... args
    );

template void
cv::winrt_startMessageLoop(void  callback void);

Detailed Documentation

Global Functions

void
cv::winrt_imshow()

Must be called to update attached image source. Code sample is available for winrt_startMessageLoop().

void
cv::winrt_onVisibilityChanged(bool visible)

Must be called from WinRT specific callback to handle image grabber state. Here is how the class can be used:

MainPage::MainPage()
{
    // ...
    Window::Current->VisibilityChanged += ref new Windows::UI::Xaml::WindowVisibilityChangedEventHandler(this, &Application::MainPage::OnVisibilityChanged);
    // ...
}

void Application::MainPage::OnVisibilityChanged(Platform::Object ^sender,
    Windows::UI::Core::VisibilityChangedEventArgs ^e)
{
    cv::winrt_onVisibilityChanged(e->Visible);
}

void
cv::winrt_setFrameContainer(::Windows::UI::Xaml::Controls::Image^ image)

Must be called to assign WinRT control holding image you’re working with. Code sample is available for winrt_startMessageLoop().

template void
cv::winrt_startMessageLoop(void  callback void)

Starts (1) frame-grabbing loop and (2) message loop

1. Function passed as an argument must implement common OCV reading frames pattern (see cv::VideoCapture documentation) AND call cv::winrt_imgshow().

2. Message processing loop required to overcome WinRT container and type conversion restrictions. OCV provides default implementation Here is how the class can be used:

   void cvMain()
   {
       Mat frame;
       VideoCapture cam;
       cam.open(0);
   
       while (1)
       {
           cam >> frame;
   
           // don't reprocess the same frame again
           if (!cam.grab()) continue;
   
           // your processing logic goes here
   
           // obligatory step to get XAML image component updated
           winrt_imshow();
       }
   }
   
   MainPage::MainPage()
   {
       InitializeComponent();
   
       cv::winrt_setFrameContainer(cvImage);
       cv::winrt_startMessageLoop(cvMain);
   }