Emscripten提示未用requestAnimationFrame，但已设0fps的问题排查

Hey there! Let's figure out why you're still seeing that annoying warning even after setting 0 for the frame rate in emscripten_set_main_loop_arg. Here are the most common fixes to check:

• Check for conflicting main loop calls
  If your code has any other main loop setup (like emscripten_set_main_loop without the _arg suffix, or manual setInterval/setTimeout calls in your JS glue code), Emscripten might detect those as non-requestAnimationFrame loops and trigger the warning. Make sure all your main loop logic is routed through emscripten_set_main_loop_arg with fps=0, and cancel any old loops first.

• Verify your parameter order
  Double-check you're passing the fps parameter correctly. The signature for emscripten_set_main_loop_arg is:

  void emscripten_set_main_loop_arg(em_arg_callback_func func, void *arg, int fps, int simulate_infinite_loop)
  

  It's easy to mix up the third (fps) and fourth (simulate_infinite_loop) parameters. If you accidentally passed 0 to the wrong argument, that would explain why the warning persists.

• Remove blocking code from your loop callback
  requestAnimationFrame relies on the browser's frame scheduling, which gets blocked if your loop callback has long-running synchronous code (like a tight while loop that doesn't yield). Even with fps=0, if your callback is hogging the main thread, Emscripten can't use requestAnimationFrame properly, so it falls back to a different loop mechanism and throws the warning. Keep your callback logic lean and avoid blocking operations.

• Cancel old loops before setting a new one
  If you're reinitializing the main loop anywhere in your code, make sure to call emscripten_cancel_main_loop() first. Leftover old loops can run in parallel with your new setup, causing Emscripten to detect non-requestAnimationFrame activity.

• Update your Emscripten version
  Some older Emscripten builds had bugs with emscripten_set_main_loop_arg and the fps=0 flag. Try updating to the latest stable version of Emscripten—this might resolve the issue if it's a known bug that's already been fixed.

Example of Correct Usage #

Here's a quick snippet showing the proper way to set up your main loop with emscripten_set_main_loop_arg:

#include <emscripten.h>

struct AppState {
    int frame_count = 0;
};

void update_loop(void* arg) {
    AppState* state = static_cast<AppState*>(arg);
    state->frame_count++;
    // Add your rendering/update logic here (keep it non-blocking!)
}

int main() {
    AppState app_state;
    
    // Cancel any existing main loops first
    emscripten_cancel_main_loop();
    
    // Set up the loop with fps=0 to use requestAnimationFrame
    emscripten_set_main_loop_arg(update_loop, &app_state, 0, 1);
    
    return 0;
}

内容的提问来源于stack exchange，提问作者FacelessTiger