Merge pull request #13176 from dmatveev:gapi_doxygen

G-API: Doxygen class reference

* G-API Doxygen documentation: covered cv::GComputation

* G-API Doxygen documentation: added sections on compile arguments

* G-API Doxygen documentation: restructuring & more text

* Added new sections (organized API reference into it);
* Documented GCompiled, compile args, backends, etc.

* G-API Doxygen documentation: documented GKernelPackage and added group for meta

modules/gapi/samples/api_ref_snippets.cpp

@@ -0,0 +1,82 @@
+#include <opencv2/videoio.hpp>
+#include <opencv2/highgui.hpp>
+#include <opencv2/gapi.hpp>
+#include <opencv2/gapi/core.hpp>
+#include <opencv2/gapi/imgproc.hpp>
+
+#include <opencv2/gapi/cpu/gcpukernel.hpp>
+
+#include <opencv2/gapi/fluid/core.hpp>
+#include <opencv2/gapi/fluid/imgproc.hpp>
+
+G_TYPED_KERNEL(IAdd, <cv::GMat(cv::GMat)>, "test.custom.add") {
+    static cv::GMatDesc outMeta(const cv::GMatDesc &in) { return in; }
+};
+G_TYPED_KERNEL(IFilter2D, <cv::GMat(cv::GMat)>, "test.custom.filter2d") {
+    static cv::GMatDesc outMeta(const cv::GMatDesc &in) { return in; }
+};
+G_TYPED_KERNEL(IRGB2YUV, <cv::GMat(cv::GMat)>, "test.custom.add") {
+    static cv::GMatDesc outMeta(const cv::GMatDesc &in) { return in; }
+};
+GAPI_OCV_KERNEL(CustomAdd,      IAdd)      { static void run(cv::Mat, cv::Mat &) {} };
+GAPI_OCV_KERNEL(CustomFilter2D, IFilter2D) { static void run(cv::Mat, cv::Mat &) {} };
+GAPI_OCV_KERNEL(CustomRGB2YUV,  IRGB2YUV)  { static void run(cv::Mat, cv::Mat &) {} };
+
+int main(int argc, char *argv[])
+{
+    if (argc < 3)
+        return -1;
+
+    cv::Mat input = cv::imread(argv[1]);
+    cv::Mat output;
+
+    {
+    //! [graph_def]
+    cv::GMat in;
+    cv::GMat gx = cv::gapi::Sobel(in, CV_32F, 1, 0);
+    cv::GMat gy = cv::gapi::Sobel(in, CV_32F, 0, 1);
+    cv::GMat g  = cv::gapi::sqrt(cv::gapi::mul(gx, gx) + cv::gapi::mul(gy, gy));
+    cv::GMat out = cv::gapi::convertTo(g, CV_8U);
+    //! [graph_def]
+
+    //! [graph_decl_apply]
+    //! [graph_cap_full]
+    cv::GComputation sobelEdge(cv::GIn(in), cv::GOut(out));
+    //! [graph_cap_full]
+    sobelEdge.apply(input, output);
+    //! [graph_decl_apply]
+
+    //! [apply_with_param]
+    cv::gapi::GKernelPackage kernels = cv::gapi::combine
+        (cv::gapi::core::fluid::kernels(),
+         cv::gapi::imgproc::fluid::kernels(),
+         cv::unite_policy::KEEP);
+    sobelEdge.apply(input, output, cv::compile_args(kernels));
+    //! [apply_with_param]
+
+    //! [graph_cap_sub]
+    cv::GComputation sobelEdgeSub(cv::GIn(gx, gy), cv::GOut(out));
+    //! [graph_cap_sub]
+    }
+    //! [graph_gen]
+    cv::GComputation sobelEdgeGen([](){
+            cv::GMat in;
+            cv::GMat gx = cv::gapi::Sobel(in, CV_32F, 1, 0);
+            cv::GMat gy = cv::gapi::Sobel(in, CV_32F, 0, 1);
+            cv::GMat g  = cv::gapi::sqrt(cv::gapi::mul(gx, gx) + cv::gapi::mul(gy, gy));
+            cv::GMat out = cv::gapi::convertTo(g, CV_8U);
+            return cv::GComputation(in, out);
+        });
+    //! [graph_gen]
+
+    cv::imwrite(argv[2], output);
+
+    //! [kernels_snippet]
+    cv::gapi::GKernelPackage pkg = cv::gapi::kernels
+        < CustomAdd
+        , CustomFilter2D
+        , CustomRGB2YUV
+        >();
+    //! [kernels_snippet]
+    return 0;
+}