godot/platform/javascript/javascript_main.cpp

/*************************************************************************/
/*  javascript_main.cpp                                                  */
/*************************************************************************/
/*                       This file is part of:                           */
/*                           GODOT ENGINE                                */
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/* Copyright (c) 2014-2022 Godot Engine contributors (cf. AUTHORS.md).   */
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#include "core/config/engine.h"
#include "core/io/resource_loader.h"
#include "main/main.h"
#include "platform/javascript/display_server_javascript.h"
#include "platform/javascript/os_javascript.h"

#include <emscripten/emscripten.h>
#include <stdlib.h>

#include "godot_js.h"

static OS_JavaScript *os = nullptr;
static uint64_t target_ticks = 0;

void exit_callback() {
	emscripten_cancel_main_loop(); // After this, we can exit!
	Main::cleanup();
	int exit_code = OS_JavaScript::get_singleton()->get_exit_code();
	memdelete(os);
	os = nullptr;
	emscripten_force_exit(exit_code); // No matter that we call cancel_main_loop, regular "exit" will not work, forcing.
}

void cleanup_after_sync() {
	emscripten_set_main_loop(exit_callback, -1, false);
}

void main_loop_callback() {
	uint64_t current_ticks = os->get_ticks_usec();

	bool force_draw = DisplayServerJavaScript::get_singleton()->check_size_force_redraw();
	if (force_draw) {
		Main::force_redraw();
	} else if (current_ticks < target_ticks) {
		return; // Skip frame.
	}

	int target_fps = Engine::get_singleton()->get_target_fps();
	if (target_fps > 0) {
		if (current_ticks - target_ticks > 1000000) {
			// When the window loses focus, we stop getting updates and accumulate delay.
			// For this reason, if the difference is too big, we reset target ticks to the current ticks.
			target_ticks = current_ticks;
		}
		target_ticks += (uint64_t)(1000000 / target_fps);
	}
	if (os->main_loop_iterate()) {
		emscripten_cancel_main_loop(); // Cancel current loop and wait for cleanup_after_sync.
		godot_js_os_finish_async(cleanup_after_sync);
	}
}

/// When calling main, it is assumed FS is setup and synced.
extern EMSCRIPTEN_KEEPALIVE int godot_js_main(int argc, char *argv[]) {
	os = new OS_JavaScript();

	// We must override main when testing is enabled
	TEST_MAIN_OVERRIDE

	Main::setup(argv[0], argc - 1, &argv[1]);

	// Ease up compatibility.
	ResourceLoader::set_abort_on_missing_resources(false);

	Main::start();
	os->get_main_loop()->initialize();
#ifdef TOOLS_ENABLED
	if (Engine::get_singleton()->is_project_manager_hint() && FileAccess::exists("/tmp/preload.zip")) {
		PackedStringArray ps;
		ps.push_back("/tmp/preload.zip");
		os->get_main_loop()->emit_signal(SNAME("files_dropped"), ps, -1);
	}
#endif
	emscripten_set_main_loop(main_loop_callback, -1, false);
	// Immediately run the first iteration.
	// We are inside an animation frame, we want to immediately draw on the newly setup canvas.
	main_loop_callback();

	return 0;
}