Prevent double input events on gamepad when running through steam input

During GDC and general testing on Steam Deck units, we found that single
gamepads would often register inputs twice under certain circumstances.
This was caused by SteamInput creating a new virtual device, which Godot
registers as a second gamepad. This resulted in two gamepad devices
reporting the same button presses, often leading to buggy input response
on games with no multi-device logic and other-wise could cause intended
Steam rebindings to not work as intended (for example, swapping o and x
on a playstation pad if that feature isn't supported by the game.)

SDL gets around this by taking in a list of devices that are to be
ignored. When valve sees a controller that wants to be rebound via
SteamInput, they push a new VID/PID entry onto the environment
variable `SDL_GAMECONTROLLER_IGNORE_DEVICES` for the original gamepad
so that all game inputs can be read from the virtual gamepad instead.

This leverages the same logic as we are already using SDL gamepad
related HID mappings.

core/input/input.cpp

@@ -113,6 +113,7 @@ void Input::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("get_joy_axis", "device", "axis"), &Input::get_joy_axis);
 	ClassDB::bind_method(D_METHOD("get_joy_name", "device"), &Input::get_joy_name);
 	ClassDB::bind_method(D_METHOD("get_joy_guid", "device"), &Input::get_joy_guid);
+	ClassDB::bind_method(D_METHOD("should_ignore_device", "vendor_id", "product_id"), &Input::should_ignore_device);
 	ClassDB::bind_method(D_METHOD("get_connected_joypads"), &Input::get_connected_joypads);
 	ClassDB::bind_method(D_METHOD("get_joy_vibration_strength", "device"), &Input::get_joy_vibration_strength);
 	ClassDB::bind_method(D_METHOD("get_joy_vibration_duration", "device"), &Input::get_joy_vibration_duration);
@@ -1498,6 +1499,11 @@ String Input::get_joy_guid(int p_device) const {
 	return joy_names[p_device].uid;
 }
 
+bool Input::should_ignore_device(int p_vendor_id, int p_product_id) const {
+	uint32_t full_id = (((uint32_t)p_vendor_id) << 16) | ((uint16_t)p_product_id);
+	return ignored_device_ids.has(full_id);
+}
+
 TypedArray<int> Input::get_connected_joypads() {
 	TypedArray<int> ret;
 	HashMap<int, Joypad>::Iterator elem = joy_names.begin();
@@ -1542,6 +1548,27 @@ Input::Input() {
 		}
 	}
 
+	String env_ignore_devices = OS::get_singleton()->get_environment("SDL_GAMECONTROLLER_IGNORE_DEVICES");
+	if (!env_ignore_devices.is_empty()) {
+		Vector<String> entries = env_ignore_devices.split(",");
+		for (int i = 0; i < entries.size(); i++) {
+			Vector<String> vid_pid = entries[i].split("/");
+
+			if (vid_pid.size() < 2) {
+				continue;
+			}
+
+			print_verbose(vformat("Device Ignored -- Vendor: %s Product: %s", vid_pid[0], vid_pid[1]));
+			const uint16_t vid_unswapped = vid_pid[0].hex_to_int();
+			const uint16_t pid_unswapped = vid_pid[1].hex_to_int();
+			const uint16_t vid = BSWAP16(vid_unswapped);
+			const uint16_t pid = BSWAP16(pid_unswapped);
+
+			uint32_t full_id = (((uint32_t)vid) << 16) | ((uint16_t)pid);
+			ignored_device_ids.insert(full_id);
+		}
+	}
+
 	legacy_just_pressed_behavior = GLOBAL_DEF("input_devices/compatibility/legacy_just_pressed_behavior", false);
 	if (Engine::get_singleton()->is_editor_hint()) {
 		// Always use standard behavior in the editor.

core/input/input.h

@@ -154,6 +154,9 @@ private:
 	VelocityTrack mouse_velocity_track;
 	HashMap<int, VelocityTrack> touch_velocity_track;
 	HashMap<int, Joypad> joy_names;
+
+	HashSet<uint32_t> ignored_device_ids;
+
 	int fallback_mapping = -1;
 
 	CursorShape default_shape = CURSOR_ARROW;
@@ -328,6 +331,7 @@ public:
 
 	bool is_joy_known(int p_device);
 	String get_joy_guid(int p_device) const;
+	bool should_ignore_device(int p_vendor_id, int p_product_id) const;
 	void set_fallback_mapping(String p_guid);
 
 	void flush_buffered_events();

doc/classes/Input.xml

@@ -343,6 +343,15 @@
 				[b]Note:[/b] This value can be immediately overwritten by the hardware sensor value on Android and iOS.
 			</description>
 		</method>
+		<method name="should_ignore_device" qualifiers="const">
+			<return type="bool" />
+			<param index="0" name="vendor_id" type="int" />
+			<param index="1" name="product_id" type="int" />
+			<description>
+				Queries whether an input device should be ignored or not. Devices can be ignored by setting the environment variable [code]SDL_GAMECONTROLLER_IGNORE_DEVICES[/code]. Read the [url=https://wiki.libsdl.org/SDL2]SDL documentation[/url] for more information.
+				[b]Note:[/b] Some 3rd party tools can contribute to the list of ignored devices. For example, [i]SteamInput[/i] creates virtual devices from physical devices for remapping purposes. To avoid handling the same input device twice, the original device is added to the ignore list.
+			</description>
+		</method>
 		<method name="start_joy_vibration">
 			<return type="void" />
 			<param index="0" name="device" type="int" />

platform/linuxbsd/joypad_linux.cpp

@@ -391,6 +391,16 @@ void JoypadLinux::open_joypad(const char *p_path) {
 			return;
 		}
 
+		uint16_t vendor = BSWAP16(inpid.vendor);
+		uint16_t product = BSWAP16(inpid.product);
+		uint16_t version = BSWAP16(inpid.version);
+
+		if (input->should_ignore_device(vendor, product)) {
+			// This can be true in cases where Steam is passing information into the game to ignore
+			// original gamepads when using virtual rebindings (See SteamInput).
+			return;
+		}
+
 		MutexLock lock(joypads_mutex[joy_num]);
 		Joypad &joypad = joypads[joy_num];
 		joypad.reset();
@@ -399,10 +409,6 @@ void JoypadLinux::open_joypad(const char *p_path) {
 		setup_joypad_properties(joypad);
 		sprintf(uid, "%04x%04x", BSWAP16(inpid.bustype), 0);
 		if (inpid.vendor && inpid.product && inpid.version) {
-			uint16_t vendor = BSWAP16(inpid.vendor);
-			uint16_t product = BSWAP16(inpid.product);
-			uint16_t version = BSWAP16(inpid.version);
-
 			sprintf(uid + String(uid).length(), "%04x%04x%04x%04x%04x%04x", vendor, 0, product, 0, version, 0);
 			input->joy_connection_changed(joy_num, true, name, uid);
 		} else {