Merge pull request opencv#25582 from fengyuentau:dnn/dump_pbtxt

Current net exporter `dump` and `dumpToFile` exports the network structure (and its params) to a .dot file which works with `graphviz`. This is hard to use and not friendly to new user. What's worse, the produced picture is not looking pretty.
dnn: better net exporter that works with netron opencv#25582

This PR introduces new exporter `dumpToPbtxt` and uses this new exporter by default with environment variable `OPENCV_DNN_NETWORK_DUMP`. It mimics the string output of a onnx model but modified with dnn-specific changes, see below for an example.

![image](https://github.com/opencv/opencv/assets/17219438/0644bed1-da71-4019-8466-88390698e4df)

## Usage

Call `cv::dnn::Net::dumpToPbtxt`:

```cpp
TEST(DumpNet, dumpToPbtxt) {
    std::string path = "/path/to/model.onnx";
    auto net = readNet(path);

    Mat input(std::vector<int>{1, 3, 640, 480}, CV_32F);
    net.setInput(input);

    net.dumpToPbtxt("yunet.pbtxt");
}
```

Set `export OPENCV_DNN_NETWORK_DUMP=1`

```cpp
TEST(DumpNet, env) {
    std::string path = "/path/to/model.onnx";
    auto net = readNet(path);

    Mat input(std::vector<int>{1, 3, 640, 480}, CV_32F);
    net.setInput(input);

    net.forward();
}
```

---

Note:
- `pbtxt` is registered as one of the ONNX model suffix in netron. So you can see `module: ai.onnx` and such in the model.
- We can get the string output of an ONNX model with the following script

```python
import onnx
net = onnx.load("/path/to/model.onnx")
net_str = str(net)
file = open("/path/to/model.pbtxt", "w")
file.write(net_str)
file.close()
```

### 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
- [x] The PR is proposed to the proper branch
- [ ] 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

Author: fengyuentau

apps/model-diagnostics/model_diagnostics.cpp

@@ -32,12 +32,36 @@ static std::string checkFileExists(const std::string& fileName)
          "Please, specify a full path to the file.");
 }
 
+static std::vector<int> parseShape(const std::string &shape_str) {
+    std::stringstream ss(shape_str);
+    std::string item;
+    std::vector<std::string> items;
+
+    while (std::getline(ss, item, ',')) {
+        items.push_back(item);
+    }
+
+    std::vector<int> shape;
+    for (size_t i = 0; i < items.size(); i++) {
+        shape.push_back(std::stoi(items[i]));
+    }
+    return shape;
+}
+
 std::string diagnosticKeys =
         "{ model m     | | Path to the model file. }"
         "{ config c    | | Path to the model configuration file. }"
-        "{ framework f | | [Optional] Name of the model framework. }";
-
-
+        "{ framework f | | [Optional] Name of the model framework. }"
+        "{ input0_name | | [Optional] Name of input0. Use with input0_shape}"
+        "{ input0_shape | | [Optional] Shape of input0. Use with input0_name}"
+        "{ input1_name | | [Optional] Name of input1. Use with input1_shape}"
+        "{ input1_shape | | [Optional] Shape of input1. Use with input1_name}"
+        "{ input2_name | | [Optional] Name of input2. Use with input2_shape}"
+        "{ input2_shape | | [Optional] Shape of input2. Use with input2_name}"
+        "{ input3_name | | [Optional] Name of input3. Use with input3_shape}"
+        "{ input3_shape | | [Optional] Shape of input3. Use with input3_name}"
+        "{ input4_name | | [Optional] Name of input4. Use with input4_shape}"
+        "{ input4_shape | | [Optional] Shape of input4. Use with input4_name}";
 
 int main( int argc, const char** argv )
 {
@@ -55,6 +79,17 @@ int main( int argc, const char** argv )
     std::string config = checkFileExists(argParser.get<std::string>("config"));
     std::string frameworkId = argParser.get<std::string>("framework");
 
+    std::string input0_name = argParser.get<std::string>("input0_name");
+    std::string input0_shape = argParser.get<std::string>("input0_shape");
+    std::string input1_name = argParser.get<std::string>("input1_name");
+    std::string input1_shape = argParser.get<std::string>("input1_shape");
+    std::string input2_name = argParser.get<std::string>("input2_name");
+    std::string input2_shape = argParser.get<std::string>("input2_shape");
+    std::string input3_name = argParser.get<std::string>("input3_name");
+    std::string input3_shape = argParser.get<std::string>("input3_shape");
+    std::string input4_name = argParser.get<std::string>("input4_name");
+    std::string input4_shape = argParser.get<std::string>("input4_shape");
+
     CV_Assert(!model.empty());
 
     enableModelDiagnostics(true);
@@ -63,5 +98,50 @@ int main( int argc, const char** argv )
 
     Net ocvNet = readNet(model, config, frameworkId);
 
+    std::vector<std::string> input_names;
+    std::vector<std::vector<int>> input_shapes;
+    if (!input0_name.empty() || !input0_shape.empty()) {
+        CV_CheckFalse(input0_name.empty(), "input0_name cannot be empty");
+        CV_CheckFalse(input0_shape.empty(), "input0_shape cannot be empty");
+        input_names.push_back(input0_name);
+        input_shapes.push_back(parseShape(input0_shape));
+    }
+    if (!input1_name.empty() || !input1_shape.empty()) {
+        CV_CheckFalse(input1_name.empty(), "input1_name cannot be empty");
+        CV_CheckFalse(input1_shape.empty(), "input1_shape cannot be empty");
+        input_names.push_back(input1_name);
+        input_shapes.push_back(parseShape(input1_shape));
+    }
+    if (!input2_name.empty() || !input2_shape.empty()) {
+        CV_CheckFalse(input2_name.empty(), "input2_name cannot be empty");
+        CV_CheckFalse(input2_shape.empty(), "input2_shape cannot be empty");
+        input_names.push_back(input2_name);
+        input_shapes.push_back(parseShape(input2_shape));
+    }
+    if (!input3_name.empty() || !input3_shape.empty()) {
+        CV_CheckFalse(input3_name.empty(), "input3_name cannot be empty");
+        CV_CheckFalse(input3_shape.empty(), "input3_shape cannot be empty");
+        input_names.push_back(input3_name);
+        input_shapes.push_back(parseShape(input3_shape));
+    }
+    if (!input4_name.empty() || !input4_shape.empty()) {
+        CV_CheckFalse(input4_name.empty(), "input4_name cannot be empty");
+        CV_CheckFalse(input4_shape.empty(), "input4_shape cannot be empty");
+        input_names.push_back(input4_name);
+        input_shapes.push_back(parseShape(input4_shape));
+    }
+
+    if (!input_names.empty() && !input_shapes.empty() && input_names.size() == input_shapes.size()) {
+        ocvNet.setInputsNames(input_names);
+        for (size_t i = 0; i < input_names.size(); i++) {
+            Mat input(input_shapes[i], CV_32F);
+            ocvNet.setInput(input, input_names[i]);
+        }
+
+        size_t dot_index = model.rfind('.');
+        std::string graph_filename = model.substr(0, dot_index) + ".pbtxt";
+        ocvNet.dumpToPbtxt(graph_filename);
+    }
+
     return 0;
 }

modules/dnn/include/opencv2/dnn/dnn.hpp

@@ -518,6 +518,14 @@ CV__DNN_INLINE_NS_BEGIN
          *  @see dump()
          */
         CV_WRAP void dumpToFile(CV_WRAP_FILE_PATH const String& path);
+        /** @brief Dump net structure, hyperparameters, backend, target and fusion to pbtxt file
+         *  @param path   path to output file with .pbtxt extension
+         *
+         *  Use Netron (https://netron.app) to open the target file to visualize the model.
+         *  Call method after setInput(). To see correct backend, target and fusion run after forward().
+        */
+        CV_WRAP void dumpToPbtxt(CV_WRAP_FILE_PATH const String& path);
+
         /** @brief Adds new layer to the net.
          *  @param name   unique name of the adding layer.
          *  @param type   typename of the adding layer (type must be registered in LayerRegister).

modules/dnn/src/net.cpp

@@ -216,6 +216,16 @@ void Net::dumpToFile(const String& path)
     file.close();
 }
 
+void Net::dumpToPbtxt(const String& path)
+{
+    CV_TRACE_FUNCTION();
+    CV_Assert(impl);
+    CV_Assert(!empty());
+    std::ofstream file(path.c_str());
+    file << impl->dumpToPbtxt(true);
+    file.close();
+}
+
 Ptr<Layer> Net::getLayer(int layerId) const
 {
     CV_Assert(impl);