Fix comments to review

modules/gapi/include/opencv2/gapi/infer/ie.hpp

@@ -89,13 +89,17 @@ struct ParamDesc {
     cv::optional<cv::gapi::wip::onevpl::Device> vpl_preproc_device;
     cv::optional<cv::gapi::wip::onevpl::Context> vpl_preproc_ctx;
 
-    using precision_t = int;
-    using precision_map_t = std::unordered_map<std::string, int>;
-    // NB: cv::util::monostate is default value that means precision wasn't specified.
-    using precision_variant_t = cv::util::variant<cv::util::monostate,
-                                                  precision_t,
-                                                  precision_map_t>;
-    precision_variant_t output_precision;
+    using PrecisionT = int;
+    using PrecisionMapT = std::unordered_map<std::string, PrecisionT>;
+    // NB: This parameter can contain:
+    // 1. cv::util::monostate - Don't specify precision, but use default from IR/Blob.
+    // 2. PrecisionT (CV_8U, CV_32F, ...) - Specifies precision for all output layers.
+    // 3. PrecisionMapT ({{"layer0", CV_32F}, {"layer1", CV_16F}} - Specifies precision for certain output layer.
+    // cv::util::monostate is default value that means precision wasn't specified.
+    using PrecisionVariantT = cv::util::variant<cv::util::monostate,
+                                                PrecisionT,
+                                                PrecisionMapT>;
+    PrecisionVariantT output_precision;
 
 };
 } // namespace detail
@@ -366,21 +370,23 @@ public:
 
     The function is used to set an output precision for model.
 
-    @param precision Precision in OpenCV format.
+    @param precision Precision in OpenCV format (CV_8U, CV_32F, ...)
+    will be applied to all output layers.
     @return reference to this parameter structure.
     */
-    Params<Net>& cfgOutputPrecision(detail::ParamDesc::precision_t precision) {
+    Params<Net>& cfgOutputPrecision(detail::ParamDesc::PrecisionT precision) {
         desc.output_precision = precision;
         return *this;
     }
 
     /** @overload
 
-    @param precision_map Map of pairs: name of corresponding output layer and its precision
+    @param precision_map Map of pairs: name of corresponding output layer
+    and its precision in OpenCV format (CV_8U, CV_32F, ...)
     @return reference to this parameter structure.
     */
     Params<Net>&
-    cfgOutputPrecision(detail::ParamDesc::precision_map_t precision_map) {
+    cfgOutputPrecision(detail::ParamDesc::PrecisionMapT precision_map) {
         desc.output_precision = precision_map;
         return *this;
     }
@@ -511,14 +517,14 @@ public:
     }
 
     /** @see ie::Params::cfgOutputPrecision */
-    Params& cfgOutputPrecision(detail::ParamDesc::precision_t precision) {
+    Params& cfgOutputPrecision(detail::ParamDesc::PrecisionT precision) {
         desc.output_precision = precision;
         return *this;
     }
 
     /** @overload */
     Params&
-    cfgOutputPrecision(detail::ParamDesc::precision_map_t precision_map) {
+    cfgOutputPrecision(detail::ParamDesc::PrecisionMapT precision_map) {
         desc.output_precision = precision_map;
         return *this;
     }

modules/gapi/src/backends/ie/giebackend.cpp

@@ -201,10 +201,10 @@ inline void copyFromIE(const IE::Blob::Ptr &blob, MatType &mat) {
     const auto ie_type = toCV(desc.getPrecision());
     if (ie_type != mat.type()) {
         std::stringstream ss;
-        ss << "Failed while copying blob from IE to OCV: "
-           << "Blobs have different data types.\n"
-           << "IE type: " << ie_type << "\n"
-           << "OCV type: " << mat.type() << std::endl;
+        ss << "Failed to copy blob from IE to OCV: "
+           << "Blobs have different data types "
+           << "(IE type: " << ie_type
+           << " vs OCV type: " << mat.type() << ")." << std::endl;
         throw std::logic_error(ss.str());
     }
     switch (blob->getTensorDesc().getPrecision()) {
@@ -1140,29 +1140,25 @@ static IE::PreProcessInfo configurePreProcInfo(const IE::InputInfo::CPtr& ii,
 }
 
 using namespace cv::gapi::ie::detail;
-static void configureOutputPrecision(const IE::OutputsDataMap             &outputs_info,
-                                     const ParamDesc::precision_variant_t &output_precision) {
-    switch (output_precision.index()) {
-        case ParamDesc::precision_variant_t::index_of<ParamDesc::precision_t>(): {
-            auto precision = toIE(cv::util::get<ParamDesc::precision_t>(output_precision));
-            for (auto it : outputs_info) {
-                it.second->setPrecision(precision);
-            }
-            break;
-        }
-        case ParamDesc::precision_variant_t::index_of<ParamDesc::precision_map_t>(): {
-            const auto& precision_map =
-                cv::util::get<ParamDesc::precision_map_t>(output_precision);
-            for (auto it : precision_map) {
-                outputs_info.at(it.first)->setPrecision(toIE(it.second));
+static void configureOutputPrecision(const IE::OutputsDataMap           &outputs_info,
+                                     const ParamDesc::PrecisionVariantT &output_precision) {
+    cv::util::visit(cv::util::overload_lambdas(
+            [&outputs_info](ParamDesc::PrecisionT cvdepth) {
+                auto precision = toIE(cvdepth);
+                for (auto it : outputs_info) {
+                    it.second->setPrecision(precision);
+                }
+            },
+            [&outputs_info](const ParamDesc::PrecisionMapT& precision_map) {
+                for (auto it : precision_map) {
+                    outputs_info.at(it.first)->setPrecision(toIE(it.second));
+                }
+            },
+            [&outputs_info](cv::util::monostate) {
+                // Do nothing.
             }
-            break;
-        }
-        case ParamDesc::precision_variant_t::index_of<cv::util::monostate>(): {
-            // Do nothing;
-            break;
-        }
-    }
+        ), output_precision
+    );
 }
 
 // NB: This is a callback used by async infer