Limit FPS in JS by skipping iterations.

2 files changed, 13 insertions, 0 deletions

diff --git a/platform/javascript/javascript_main.cpp b/platform/javascript/javascript_main.cpp
index a2d9031f4b..8b7bd2170f 100644
--- a/platform/javascript/javascript_main.cpp
+++ b/platform/javascript/javascript_main.cpp
@@ -36,6 +36,7 @@
 #include <emscripten/emscripten.h>
 
 static OS_JavaScript *os = nullptr;
+static uint64_t target_ticks = 0;
 
 void exit_callback() {
 	emscripten_cancel_main_loop(); // After this, we can exit!
@@ -47,9 +48,18 @@ void exit_callback() {
 }
 
 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) {
+		target_ticks += (uint64_t)(1000000 / target_fps);
 	}
 	if (os->main_loop_iterate()) {
 		emscripten_cancel_main_loop(); // Cancel current loop and wait for finalize_async.
diff --git a/platform/javascript/os_javascript.h b/platform/javascript/os_javascript.h
index f0f18b44f8..dddeef836c 100644
--- a/platform/javascript/os_javascript.h
+++ b/platform/javascript/os_javascript.h
@@ -83,6 +83,9 @@ public:
 	String get_executable_path() const;
 	virtual Error shell_open(String p_uri);
 	virtual String get_name() const;
+	// Override default OS implementation which would block the main thread with delay_usec.
+	// Implemented in javascript_main.cpp loop callback instead.
+	virtual void add_frame_delay(bool p_can_draw) {}
 	virtual bool can_draw() const;
 
 	virtual String get_cache_path() const;