[SOLVED] How to add python script to c++ code

[Yannie]

Hello All,

I’m learning to write scene in C++, and would like to use the python keyboard control script in it, any example code to show how to do this?

I tried to define a PythonScriptController pointer, but when I ran the code, it always show an error:

Unhandled exception at 0x000000001E08BF77 (python27.dll) in test.exe: 0xC0000005: Access violation reading location 0xFFFFFFFFFFFFFFFF.

Thank you!

[Hugo]

Hi Yannie,

To use Python scripts in a simulation written in C++, indeed, you need to do is to instantiate the C++ class PythonScriptController. Your C++ application must therefore have a dependency on the SofaPython plugin (explicit in CMakeList.txt).
HTH,

Hugo

[Yannie]

Thanks Hugo for the reply.

I did add sofaPython plugin. But it always gives the above error. It looks the the pythonscriptcontroller instance can’t read in the .py file.

Here is my code:

const char* filename = “keyboardControl.py”;
sofa::component::controller::PythonScriptController::SPtr pyContr = sofa::core::objectmodel::New<sofa::component::controller::PythonScriptController>();
pyContr->m_filename.setValue(filename);

I suppose the class can parse the .py file automatically once it read in?

[Hugo]

Hey Yannie,

the error shows that you are using an un-initialized data. But your code looks ok. I would have written :

#include "PythonScriptController.h"

...

int main(int argc, char** argv)
{

...

sofa::simulation::Node::SPtr groot = sofa::simulation::getSimulation()->createNewGraph("root");
groot->setGravity( Coord3(0,-10,0) );

...

std::string filename = "keyboardControl.py";
std::string classname = "yourclassname";
sofa::component::controller::PythonScriptController::SPtr pyContr = sofa::core::objectmodel::New<sofa::component::controller::PythonScriptController>();
pyContr->m_filename.setValue(filename);
pyContr->m_classname.setValue(classname);
groot->addObject(pyContr);
}

and your CMakeLists.txt should look like:

cmake_minimum_required(VERSION 3.1)
project(mytest)

find_package(SofaSimulation)
find_package(SofaPython)

add_executable(${PROJECT_NAME} test.cpp)
target_link_libraries(${PROJECT_NAME} SofaPython SofaSimulation)

HTH,

Hugo

[Yannie]

Thanks Hugo!
I’ve play around a bit, it still has this problem, I’m able to locate where the error come but not sure how to solve it. So the code run into the python error at this line:

sofa::simulation::getSimulation()->init(groot.get());

And I can trace it to PythonScriptController::script_initGraph(Node *node), it gave the exception at here.

Does it has something to do with the m_classname? I assume it should be the classname in Python script. Then I tried to just type some simple code in python, like

def createScene(node):

    def hello():
        print 'hello !'

But still, no luck.
Any thoughts? Thanks!

[Hugo]

Hi Yannie

Could you please post the complete Python script ? Python scripts are sensitive to tabulations. Seeing the entire script would help,

Thank you !

[Yannie]

The script I posted above is the whole script. For this script, I didn’t add m_classname as there is no class name in it.

I also tried the PythonScriptController_Placeholders.py in the sofaPython examples folder and set the m_classname to ExampleController, same problem!

Thanks!

[Hugo]

Hi Yannie,

You tried PythonScriptController_Placeholders.py in your C++ scene and it did not work ?
In your C++ scene, you instantiated a PythonScripController with the data filename set to PythonScriptController_Placeholders.py and the data classname set to the string ExampleController ?

Have you tried to specify in you C++ scene, a RequiredPlugin with the data pluginName set to SofaPython ?

HTH

Hugo

[Yannie]

Thanks Hugo,

Well, I debugged for some time and found that the PythonScripController.cpp constructor doesn’t call loadscript(), so I write add a new constructor and rebuilt sofaPython and it worked. I seems that the PythonScripController was written for use cases that read scene files instead of constructor the object in code, because it does work if I just load the .scn file for runsofa. I could be wrong as I don’t know the platform well enough. Does it work for you if you just assign filename and classname?

Additional question. So I tried the keyboardcontrol.py again, but my object doesn’t move and the error is mechanicalState.free_position index out range. And I print out free_position, it is empty, when and where this free_position is initiated?

Thanks again!
Yannie

[Hugo]

Dear Yannie,

Your question has been discussed at the weekly dev meeting (you can follow the agenda and report by subscribing to the sofa-dev mailing list).
Here is the answer I got:

• a question on the forum about SofaPython in a C++ scene: the best is to initialize the python environment using the PluginManager (sofa::helper::system::PluginManager). Thus, you are able to directly load the python environment
• about the initialization of free_position (in the MultiVector of the MechanicalState), it is created when a FreeAnimationLoop is created if I remember properly. Otherwise, it won’t be allocated.

HTH
Best,

Hugo

[Yannie]

Thanks Hugo!

I did use the PluginManager to load the SofaPython as well as adding RequiredPlugin node, not sure why it didn’t call loadscript with that setting.

Thanks, the FreeMotionAnimationLoop does help, now I can move object around!

Best,
Yannie

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