Merge pull request #12674 from dmatveev:gapi_upd270918

* Update G-API code base to 27-Sep-18

Changes mostly improve standalone build support

* G-API code base update 28-09-2018

* Windows/Documentation warnings should be fixed
* Fixed stability issues in Fluid backend
* Fixed precompiled headers issues in G-API source files

* G-API code base update 28-09-18 EOD

* Fixed several static analysis issues
* Fixed issues found when G-API is built in a standalone mode

modules/gapi/src/executor/gexecutor.cpp

@@ -5,11 +5,13 @@
 // Copyright (C) 2018 Intel Corporation
 
 
+#include "precomp.hpp"
+
 #include <iostream>
 
 #include <ade/util/zip_range.hpp>
 
-#include "opencv2/core/types.hpp"
+#include "opencv2/gapi/opencv_includes.hpp"
 #include "executor/gexecutor.hpp"
 
 cv::gimpl::GExecutor::GExecutor(std::unique_ptr<ade::Graph> &&g_model)
@@ -150,8 +152,21 @@ void cv::gimpl::GExecutor::run(cv::gimpl::GRuntimeArgs &&args)
             using cv::util::get;
             const auto desc = get<cv::GMatDesc>(d.meta);
             const auto type = CV_MAKETYPE(desc.depth, desc.chan);
+
+#if !defined(GAPI_STANDALONE)
+            // Building as part of OpenCV - follow OpenCV behavior
+            // if output buffer is not enough to hold the result, reallocate it
             auto& out_mat   = *get<cv::Mat*>(args.outObjs.at(index));
             out_mat.create(cv::gapi::own::to_ocv(desc.size), type);
+#else
+            // Building standalone - output buffer should always exist,
+            // and _exact_ match our inferred metadata
+            auto& out_mat   = *get<cv::gapi::own::Mat*>(args.outObjs.at(index));
+            GAPI_Assert(   out_mat.type() == type
+                        && out_mat.data   != nullptr
+                        && out_mat.rows   == desc.size.height
+                        && out_mat.cols   == desc.size.width)
+#endif // !defined(GAPI_STANDALONE)
         }
     }
     // Update storage with user-passed objects