What is the process for accessing external variables from Cheerp/js?

Question

What is the process for accessing external variables from Cheerp/js?

Cheerp is a tool that transpiles C++ code to js/wasm. Screeps is an interactive programming game.

How can I access the Game.time variable in my C++ code after it has been transpiled for Screeps?

#include <cheerp/client.h>
#include <iostream>
using namespace std;

namespace client {
    class Game : public Object {
    public:
        static volatile double time;
    };  

    extern volatile Game &Game;
}

void webMain() {
    cout << __TIME__ << ": The current time is: " << client::Game.time << endl;
}

I have experimented with:

extern, volatile, and static keywords
references and pointers
both client and cheerp namespaces
Inheriting from Node/Object
Different data types such as int32_t, double, and float

However, I keep encountering issues like:

NaN
0
1
fatal errors related to data types in the compiled code

What is the correct approach to interact with JavaScript objects and variables from C++ code? The documentation provided by cheerp is very limited...

Note: It seems that cheerp is not generating the correct JavaScript output. There are inconsistencies in how the Game object is handled, leading to attempts to index Game.d as an array rather than Game.time.

javascript c++llvm screeps cheerp

Answer 1

Answer №1

It is recommended that classes declared within the client namespace do not contain any member fields.

In order to access properties of external JavaScript objects, you must include methods starting with get_ and set_, which are used for reading and writing to the property respectively:

#include <cheerp/client.h>
#include <iostream>
using namespace std;

namespace client {
    class Game : public Object {
    public:
        double get_time();
    };  

    extern Game &Game;
}

void webMain() {
    cout << __TIME__ << ": The current time is: " << client::Game.get_time() << endl;
}

Additionally, there is no need to utilize the `volatile` keyword in this context.

Answer 2

It is recommended that classes declared within the client namespace do not contain any member fields.

In order to access properties of external JavaScript objects, you must include methods starting with get_ and set_, which are used for reading and writing to the property respectively:

#include <cheerp/client.h>
#include <iostream>
using namespace std;

namespace client {
    class Game : public Object {
    public:
        double get_time();
    };  

    extern Game &Game;
}

void webMain() {
    cout << __TIME__ << ": The current time is: " << client::Game.get_time() << endl;
}

Additionally, there is no need to utilize the `volatile` keyword in this context.

What is the process for accessing external variables from Cheerp/js?

Answer №1

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