{"id":109558,"date":"2024-03-21T07:00:00","date_gmt":"2024-03-21T14:00:00","guid":{"rendered":"https:\/\/devblogs.microsoft.com\/oldnewthing\/?p=109558"},"modified":"2024-03-21T08:45:36","modified_gmt":"2024-03-21T15:45:36","slug":"20240321-00","status":"publish","type":"post","link":"https:\/\/devblogs.microsoft.com\/oldnewthing\/20240321-00\/?p=109558","title":{"rendered":"Using the Display­Information<\/CODE> class from a desktop Win32 application, part 2"},"content":{"rendered":"

Last time, we tried to create a Display\u00adInformation<\/code> from an HWND<\/code><\/a>, but it failed with the message “A DispatcherQueue is required for DisplayInformation created from an HWND.”<\/p>\n

So I guess we need to make sure the thread has a Dispatcher\u00adQueue<\/code>.<\/p>\n

#include <DispatcherQueue.h><\/span>\r\n#include <windows.graphics.display.interop.h>\r\n#include <winrt\/Windows.Graphics.Display.h>\r\n#include <winrt\/Windows.Foundation.h><\/span>\r\n#include <winrt\/Windows.System.h>    <\/span>\r\n\r\nnamespace winrt\r\n{\r\n    using namespace winrt::Windows::Graphics::Display;\r\n    using namespace winrt::Windows::System;<\/span>\r\n}\r\n\r\nnamespace ABI                            <\/span>\r\n{                                        <\/span>\r\n    using namespace ABI::Windows::System;<\/span>\r\n}                                        <\/span>\r\nwinrt::DispatcherQueueController g_controller{ nullptr };<\/span>\r\nwinrt::DisplayInformation g_info{ nullptr };\r\n\r\nOnCreate(HWND hwnd, LPCREATESTRUCT lpcs) noexcept\r\n{\r\n    DispatcherQueueOptions options{                              <\/span>\r\n        sizeof(options), DQTYPE_THREAD_CURRENT, DQTAT_COM_NONE };<\/span>\r\n    winrt::check_hresult(                                        <\/span>\r\n        CreateDispatcherQueueController(options,                 <\/span>\r\n            reinterpret_cast<ABI::IDispatcherQueueController**>( <\/span>\r\n                controller.put())));                             <\/span>\r\n\r\n    g_info = wil::capture_interop<winrt::DisplayInformation>\r\n        (&IDisplayInformationStaticsInterop::GetForWindow, hwnd);\r\n\r\n    return TRUE;\r\n}\r\ncatch (...)\r\n{\r\n    return FALSE;\r\n}\r\n\r\nwinrt::fire_and_forget<\/span>\r\nOnDestroy(HWND hwnd)\r\n{\r\n    g_info = nullptr;\r\n    co_await g_controller.ShutdownQueueAsync();<\/span>\r\n    PostQuitMessage(0);\r\n}\r\n<\/pre>\n
Hooray, this code now successfully creates a Dispatcher\u00adQueue\u00adController<\/code> that manages a Dispatcher\u00adQueue<\/code>\u00a0on the current thread, and that removes the obstacle that was preventing Get\u00adFor\u00adWindow<\/code> from succeeding.<\/p>\n
Now we can hook up the event and start reading the orientation.<\/p>\n
OnCreate(HWND hwnd, LPCREATESTRUCT lpcs) noexcept\r\n{\r\n    DispatcherQueueOptions options{\r\n        sizeof(options), DQTYPE_THREAD_CURRENT, DQTAT_COM_NONE };\r\n    winrt::check_hresult(\r\n        CreateDispatcherQueueController(options,\r\n            reinterpret_cast<ABI::IDispatcherQueueController**>(\r\n                controller.put())));\r\n\r\n    g_info.OrientationChanged([hwnd](auto&&, auto&&)              <\/span>\r\n        {                                                         <\/span>\r\n            InvalidateRect(hwnd, nullptr, TRUE);                  <\/span>\r\n        });                                                       <\/span>\r\n\r\n    g_info = wil::capture_interop<winrt::DisplayInformation>\r\n        (&IDisplayInformationStaticsInterop::GetForWindow, hwnd);\r\n\r\n    return TRUE;\r\n}\r\ncatch (...)\r\n{\r\n    return FALSE;\r\n}\r\n\r\nvoid\r\nPaintContent(HWND hwnd, PAINTSTRUCT* pps) noexcept<\/span>\r\n{\r\n    PCWSTR message;                                   <\/span>\r\n    switch (g_info.CurrentOrientation()) {            <\/span>\r\n    case winrt::DisplayOrientations::Landscape:       <\/span>\r\n        message = L\"Landscape\"; break;                <\/span>\r\n    case winrt::DisplayOrientations::Portrait:        <\/span>\r\n        message = L\"Portrait\"; break;                 <\/span>\r\n    case winrt::DisplayOrientations::LandscapeFlipped:<\/span>\r\n        message = L\"LandscapeFlipped\"; break;         <\/span>\r\n    case winrt::DisplayOrientations::PortraitFlipped: <\/span>\r\n        message = L\"PortraitFlipped\"; break;          <\/span>\r\n    default:                                          <\/span>\r\n        message = L\"Unknown\"; break;                  <\/span>\r\n    }                                                 <\/span>\r\n    TextOut(pps->hdc, 0, 0, message,                  <\/span>\r\n        static_cast<int>(wcslen(message)));           <\/span>\r\n}<\/pre>\n
After creating the Display\u00adInformation<\/code>, we register for the orientation change event and force a repaint when that happens.<\/p>\n
Our paint handler simply prints the current orientation of the monitor that the window is on.<\/p>\n
I won’t bother demonstrating it here, but you can also use Get\u00adFor\u00adMonitor<\/code> to get a Display\u00adInformation<\/code> for a specific monitor.<\/p>\n
\u00a0<\/pre>\n","protected":false},"excerpt":{"rendered":"
Completing the prerequisites.<\/p>\n","protected":false},"author":1069,"featured_media":111744,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[1],"tags":[25],"class_list":["post-109558","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-oldnewthing","tag-code"],"acf":[],"blog_post_summary":"
Completing the prerequisites.<\/p>\n","_links":{"self":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts\/109558","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/users\/1069"}],"replies":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/comments?post=109558"}],"version-history":[{"count":0,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts\/109558\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/media\/111744"}],"wp:attachment":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/media?parent=109558"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/categories?post=109558"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/tags?post=109558"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
We use Create\u00adDispatcher\u00adQueue\u00adController<\/code> to attach a dispatcher queue to our existing message pump. There is a bit of a hassle with the second parameter because we are mixing the C++\/WinRT and Win32 ABI versions of the IDispatcher\u00adQueue\u00adController<\/code> interfaces. (Previous discussion<\/a>.) And since we created the dispatcher queue controller, we also have to  shut down the dispatcher queue when we’re done<\/a>, which we take care of in OnDestroy()<\/code>.<\/p>\n