main loop callbacks

module/pyjs/core.py

@@ -6,6 +6,8 @@
 import ast
 import pyjs_core
 from pyjs_core import JsValue, js_array, js_py_object
+import warnings
+import time
 
 def install_submodules():
     def _js_mod__getattr__(name: str) -> Any:
@@ -307,3 +309,49 @@ async def async_exec_eval(stmts, globals=None, locals=None):
     parsed_fn.body[0].body = parsed_stmts.body
     exec(compile(parsed_fn, filename="<ast>", mode="exec"), globals, locals)
     return await  eval(f'{fn_name}()', globals, locals)  # fmt: skip
+
+
+
+class _CallbackEntryPoint:
+    def __init__(self, py_callback):
+        self._py_callback = py_callback
+        self._last_time = time.time()
+    def __call__(self):
+        t =  time.time()
+        dt = t - self._last_time
+        self._last_time = t
+        self._py_callback(dt)
+
+_callback_entry_point = None
+
+
+def set_main_loop_callback(py_callback, fps=0):
+
+    global  _callback_entry_point
+    if _callback_entry_point is not None:
+        # show a warning if the callback is already set
+        warnings.warn(""" A main loop callback is already set. 
+            This will be replaced by the new callback,
+            use cancel_main_loop before setting a new callback to avoid this warning
+            """,
+            UserWarning)
+
+        cancel_main_loop()
+
+    _callback_entry_point = _CallbackEntryPoint(py_callback)
+
+    pyjs_core._set_main_loop_callback(
+        _callback_entry_point,
+        int(fps)
+    )
+
+
+def cancel_main_loop():
+    """Cancel the main loop callback."""
+    global _callback_entry_point
+    if _callback_entry_point is not None:
+        pyjs_core._cancel_main_loop()
+        pyjs_core._set_noop_main_loop()
+        _callback_entry_point = None
+    else:
+        warnings.warn("No main loop callback is set to cancel.", UserWarning)

src/export_pyjs_module.cpp

@@ -16,25 +16,98 @@ namespace py = pybind11;
 namespace em = emscripten;
 
 namespace pyjs
-{
+{   
+
+    // struct LoopContext
+    // {
+    //     py::object m_callback;
+    //     bool m_cancel_loop_on_error = true; // default to true
+    //     bool m_exit_loop = false;
+
+    //     LoopContext(py::object callback, bool cancel_loop_on_error)
+    //         : m_callback(std::move(callback)), m_cancel_loop_on_error(cancel_loop_on_error), m_exit_loop(false) {}
+    // };
+
+
+    void wrapped_callback(void* cb_ptr) {
+        // Reinterpret the void pointer back to a PyObject pointer
+        auto py_object = reinterpret_cast<PyObject*>(cb_ptr);
+        if(!py_object) {
+            std::cerr << "Error: callback pointer is null." << std::endl;
+        }
+        // We can use PyObject_CallObject to call the Python function
+        if (PyObject_CallNoArgs(py_object) == nullptr) {
+            // If the call fails, we can print the error
+            std::cerr << "Error calling Python callback:" << std::endl;
+            PyErr_Print();
+        }
+    };
+
+    void noop_callback() {
+        // This is a no-op callback, it does nothing
+
+        // we see a strange error when we run emscripten_cancel_main_loop
+        // **WITHOUT setting a new loop right away**
+        // so instead of just cancelling the loop, we need
+        // to cancel and right away set a new loop
+    }
+
+    void self_cancel_callback() {
+       emscripten_cancel_main_loop();
+    };
+
+
+    void export_main_loop_callbacks(py::module_& pyjs_module)
+    {
+
+
+
+        // // class for loop context
+        // py::class_<LoopContext>(pyjs_module, "LoopContext")
+        //     .def(py::init<py::object, bool>(), py::arg("callback"), py::arg("cancel_loop_on_error") = true)
+        //     .def_readwrite("exit_loop", &LoopContext::m_exit_loop)
+        // ;
+
+
+
+        // Export main loop callbacks
+        pyjs_module.def("_set_main_loop_callback", [](py::handle  callback, int fps) {
+
+            // get a PyObject * from the handle
+            auto py_object = callback.ptr();
+
+            // convert the PyObject to void*
+            void* callback_ptr = reinterpret_cast<void*>(py_object);
+
+
+            // use emscripten_set_main_loop_arg
+            emscripten_set_main_loop_arg(
+                wrapped_callback,
+                callback_ptr, // pass the callback pointer as argument
+                fps, // frames per second
+                false 
+            );
+        });
+
+        // explicit cancel main loop
+        pyjs_module.def("_cancel_main_loop", []() {
+            // This will cancel the main loop if it is currently running
+            emscripten_cancel_main_loop();
+        });
+
+        pyjs_module.def("_set_noop_main_loop", []() {
+            // This will set a no-op main loop
+            emscripten_set_main_loop(noop_callback, 1, false); // set a no-op loop to avoid errors
+        });
+
+    }
+
+
+
     void export_pyjs_module(py::module_& pyjs_module)
     {
         export_js_proxy(pyjs_module);
-        try
-        {
-            // pyjs_core_pseudo_init(pyjs_module);
-            // pyjs_extend_js_val_pseudo_init(pyjs_module);
-            // pyjs_error_handling_pseudo_init(pyjs_module);
-            // pyjs_convert_pseudo_init(pyjs_module);
-            // pyjs_convert_py_to_js_pseudo_init(pyjs_module);
-            // pyjs_webloop_pseudo_init(pyjs_module);
-            // pyjs_pyodide_polyfill_pseudo_init(pyjs_module);
-        }
-        catch (py::error_already_set& e)
-        {            
-            std::cout << "error: " << e.what() << "\n";
-            throw e;
-        }
+        export_main_loop_callbacks(pyjs_module);
 
     }
 }