Merge pull request #25354 from LaurentBerger:uiname

Add cv::currentUIFramework #25354

issue https://github.com/opencv/opencv/issues/25329

### Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

- [x] I agree to contribute to the project under Apache 2 License.
- [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
- [ ] The PR is proposed to the proper branch
- [x] There is a reference to the original bug report and related work
- [ ] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
      Patch to opencv_extra has the same branch name.
- [x] The feature is well documented and sample code can be built with the project CMake

modules/highgui/include/opencv2/highgui.hpp

@@ -285,6 +285,15 @@ The function destroyAllWindows destroys all of the opened HighGUI windows.
  */
 CV_EXPORTS_W void destroyAllWindows();
 
+
+/** @brief HighGUI backend used.
+
+The function returns HighGUI backend name used: could be COCOA, GTK2/3, QT, WAYLAND or WIN32.
+Returns empty string if there is no available UI backend.
+ */
+CV_EXPORTS_W const std::string currentUIFramework();
+
+
 CV_EXPORTS_W int startWindowThread();
 
 /** @brief Similar to #waitKey, but returns full key code.

modules/highgui/src/backend.hpp

@@ -106,6 +106,7 @@ public:
 
     virtual int waitKeyEx(int delay /*= 0*/) = 0;
     virtual int pollKey() = 0;
+    virtual const std::string getName() const = 0;
 };
 
 std::shared_ptr<UIBackend>& getCurrentUIBackend();

modules/highgui/src/window.cpp

@@ -1091,6 +1091,33 @@ void cv::imshow(const String& winname, const ogl::Texture2D& _tex)
 #endif
 }
 
+const std::string cv::currentUIFramework()
+{
+    CV_TRACE_FUNCTION();
+
+    // plugin and backend-compatible implementations
+    auto backend = getCurrentUIBackend();
+    if (backend)
+    {
+        return backend->getName();
+    }
+
+    // builtin backends
+#if defined(HAVE_WIN32UI)
+    CV_Assert(false); // backend-compatible
+#elif defined (HAVE_GTK)
+    CV_Assert(false); // backend-compatible
+#elif defined (HAVE_QT)
+    return std::string("QT");
+#elif defined (HAVE_COCOA)
+    return std::string("COCOA");
+#elif defined (HAVE_WAYLAND)
+    return std::string("WAYLAND");
+#else
+    return std::string();
+#endif
+}
+
 // Without OpenGL
 
 #ifndef HAVE_OPENGL

modules/highgui/src/window_gtk.cpp

@@ -2286,6 +2286,19 @@ public:
     {
         return cvWaitKey(1);  // TODO
     }
+
+    const std::string getName() const CV_OVERRIDE
+    {
+#if GTK_MAJOR_VERSION == 2
+        return "GTK2";
+#elif GTK_MAJOR_VERSION == 3
+        return "GTK3";
+#elif GTK_MAJOR_VERSION == 4
+        return "GTK4";
+#else
+#error "Unsupported GTK version"
+#endif
+    }
 };  // GTKBackendUI
 
 static

modules/highgui/src/window_w32.cpp

@@ -3004,6 +3004,11 @@ public:
     {
         return pollKey_W32();
     }
+
+    const std::string getName() const CV_OVERRIDE
+    {
+        return "WIN32";
+    }
 };  // Win32BackendUI
 
 static

modules/highgui/test/test_gui.cpp

@@ -205,4 +205,23 @@ TEST(Highgui_GUI, trackbar)
     EXPECT_NO_THROW(destroyAllWindows());
 }
 
+
+TEST(Highgui_GUI, currentUIFramework)
+{
+    auto framework = currentUIFramework();
+    std::cout << "UI framework: \"" << framework << "\"" << std::endl;
+#if (!defined(ENABLE_PLUGINS) \
+        && !defined HAVE_GTK \
+        && !defined HAVE_QT \
+        && !defined HAVE_WIN32UI \
+        && !defined HAVE_COCOA \
+        && !defined HAVE_WAYLAND \
+    )
+    EXPECT_TRUE(framework.empty());
+#elif !defined(ENABLE_PLUGINS)
+    EXPECT_GT(framework.size(), 0);  // builtin backends
+#endif
+}
+
+
 }} // namespace