Merge pull request #19322 from TolyaTalamanov:at/python-callbacks

[G-API] Introduce cv.gin/cv.descr_of for python

* Implement cv.gin/cv.descr_of

* Fix macos build

* Fix gcomputation tests

* Add test

* Add using to a void exceeded length for windows build

* Add using to a void exceeded length for windows build

* Fix comments to review

* Fix comments to review

* Update from latest master

* Avoid graph compilation to obtain in/out info

* Fix indentation

* Fix comments to review

* Avoid using default in switches

* Post output meta for giebackend

modules/gapi/misc/python/test/test_gapi_streaming.py

@@ -19,7 +19,7 @@ class test_gapi_streaming(NewOpenCVTests):
         g_in = cv.GMat()
         g_out = cv.gapi.medianBlur(g_in, 3)
         c = cv.GComputation(g_in, g_out)
-        ccomp = c.compileStreaming(cv.descr_of(cv.gin(in_mat)))
+        ccomp = c.compileStreaming(cv.descr_of(in_mat))
         ccomp.setSource(cv.gin(in_mat))
         ccomp.start()
 
@@ -191,7 +191,9 @@ class test_gapi_streaming(NewOpenCVTests):
                 # NB: OpenCV & G-API have different output shapes:
                 # OpenCV - (num_points, 1, 2)
                 # G-API  - (num_points, 2)
-                self.assertEqual(0.0, cv.norm(e.flatten(), a.flatten(), cv.NORM_INF))
+                self.assertEqual(0.0, cv.norm(e.flatten(),
+                                              np.array(a, np.float32).flatten(),
+                                              cv.NORM_INF))
 
             proc_num_frames += 1
             if proc_num_frames == max_num_frames: