Godot Mouse Signals Not Updating When Static: A Fix

Hey there, fellow game devs! Ever run into a head-scratcher where your Godot game's mouse interactions just weren't behaving as expected? Specifically, have you noticed that the mouse_entered and mouse_exited signals on Control nodes don't always fire when the mouse is perfectly still? Yeah, it's a bit of a quirk, but thankfully, there's a way around it. Let's dive into this issue, understand why it happens, and explore a straightforward solution to keep your UI interactions snappy and responsive, even when the player is playing the waiting game.

Understanding the Core Issue: Static Mouse, Dynamic Controls

The heart of the problem lies in how Godot handles input and collision detection, particularly when the mouse isn't moving. The bug specifically affects scenarios where a Control node is moving (or its size or position is changing), while the mouse cursor itself is stationary. Normally, you'd expect mouse_entered to trigger when the mouse cursor enters the bounds of a Control node, and mouse_exited to fire when it leaves. However, due to how the engine's collision system works, these signals aren't always immediately updated when the mouse is static and the Control node is the one in motion.

Basically, Godot's system, for optimization reasons, might not constantly check the mouse position against every moving Control node if the mouse itself isn't moving. It's a bit like the engine is saying, "Hey, if the mouse isn't moving, there's no need to constantly recalculate these collisions." This approach can save on processing power, but it leads to the behavior you've observed.

Reproducing the Issue

To really see this in action, imagine a simple scenario: you've got a Control node (like a button or label) that's smoothly moving across the screen. You place your mouse cursor over this Control node. According to your game's logic, the Control node's color should change when the mouse is over it. If the Control node then moves out from under the cursor, you'd expect the color to revert back. However, if the mouse is still, the mouse_exited signal might not trigger until the mouse itself moves again. This is precisely the problem we're tackling!

To clarify, the issue is that the signals don't update when the Control node's position changes and the mouse stays put. The signals do update as expected when the mouse is moving or if the Control node's position doesn't change.

Code Example and Explanation

Here’s a simplified example, mirroring the code provided in the problem description, demonstrating the issue:

extends Control

var mouse_over = false
var time_passed = 0.
@onready var label = %Label

func _ready():
    mouse_entered.connect(_on_mouse_entered)
    mouse_exited.connect(_on_mouse_exited)

func _process(delta):
    time_passed += delta
    position.x = sin(time_passed) * 100. + 500.
    label.text = "mouse over" if mouse_over else "mouse not over"
    label.modulate = Color.GREEN if mouse_over else Color.RED

func _on_mouse_entered():
    print_debug("Mouse entered control node")
    mouse_over = true

func _on_mouse_exited():
    print_debug("Mouse exited control node")
    mouse_over = false

In this code:

• The Control node's position.x is updated in _process(), causing it to move horizontally across the screen.
• _on_mouse_entered() and _on_mouse_exited() are connected to the respective signals. They change the mouse_over flag and update the text and color of a label.
• The bug appears because the signals don't always fire immediately when the mouse is still.

This simple setup illustrates the problem perfectly. The visual feedback (label text and color) won't always update immediately when the moving Control node's bounds change relative to the stationary mouse cursor.

The Fix: Force the Check

The simplest and most effective solution involves a little bit of force. We can make sure that Godot re-evaluates the mouse position relative to our Control nodes more frequently. The core strategy is to detect when a Control node's position, size, or any relevant properties change and then manually trigger the checks that would normally be done by the engine. Here are the core strategies to tackle this:

1. _process()-Based Approach

This is perhaps the most straightforward way, using _process() to regularly check for mouse-over conditions.

extends Control

var mouse_over = false
@onready var label = %Label

func _ready():
    set_process_input(true)

func _process(delta):
    var is_over = get_global_rect().has_point(get_global_mouse_position())

    if is_over != mouse_over:
        mouse_over = is_over
        if mouse_over:
            _on_mouse_entered()
        else:
            _on_mouse_exited()

    label.text = "mouse over" if mouse_over else "mouse not over"
    label.modulate = Color.GREEN if mouse_over else Color.RED

func _on_mouse_entered():
    print_debug("Mouse entered control node")
    mouse_over = true

func _on_mouse_exited():
    print_debug("Mouse exited control node")
    mouse_over = false

In this version:

• _process() checks every frame if the mouse is over the control using get_global_rect().has_point(get_global_mouse_position()). This method ensures that the mouse position is checked against the control's current global position.
• The function compares the new state with the previous state (mouse_over). If it has changed, it manually calls the mouse enter/exit functions. Thus, this code bypasses the issue where signals aren't triggered when the mouse is static.

2. Using _input()

Another approach is to utilize the _input() function, which captures all input events. This allows you to check the mouse position on every input event.

extends Control

var mouse_over = false
@onready var label = %Label

func _ready():
    set_process_input(true)

func _input(event):
    if event is InputEventMouseMotion:
        var is_over = get_global_rect().has_point(get_global_mouse_position())
        if is_over != mouse_over:
            mouse_over = is_over
            if mouse_over:
                _on_mouse_entered()
            else:
                _on_mouse_exited()
    label.text = "mouse over" if mouse_over else "mouse not over"
    label.modulate = Color.GREEN if mouse_over else Color.RED

func _on_mouse_entered():
    print_debug("Mouse entered control node")
    mouse_over = true

func _on_mouse_exited():
    print_debug("Mouse exited control node")
    mouse_over = false

Here, the _input() function does the heavy lifting:

• It first checks if the current event is an InputEventMouseMotion. This is important, as _input() receives all input events.
• If it's a mouse motion event, it performs the same get_global_rect().has_point() check to determine if the mouse is over the control.
• If the mouse-over state has changed, it updates the mouse_over flag and manually calls the appropriate signal-handling function.

3. Using body_entered and body_exited (for physics-based approach)

If your control nodes are part of a physics-based scene, you can use body_entered and body_exited signals to detect when a rigid body or other physics objects enter or exit the control node's area. This approach might be less relevant for UI controls, but it can be useful in other scenarios.

Implementation Details and Considerations

When implementing either of the proposed solutions, keep a few things in mind:

• Performance: If you're dealing with a large number of moving Control nodes, using _process() every frame can potentially impact performance. Consider optimizing the check by only enabling it when a specific condition is met, such as when the node's position is actually changing. The _input method can be more efficient, since it is only triggered when there is an input event.
• Efficiency: Try to cache values whenever possible. For example, if the Control node's global_rect is constant between frames, cache it in the _ready function.
• Node Hierarchy: Remember that the get_global_rect() method is dependent on the Control node's position within the scene's node hierarchy. If the node's position is affected by its parents, the result from get_global_rect() will include these parent transformations.
• Testing: Thoroughly test your solution under various conditions. Ensure that the mouse interactions behave as expected when the mouse is static, moving slowly, and moving quickly. Test on different hardware and operating systems to ensure consistent behavior.

Conclusion: Keeping Your UI Responsive

In essence, the key to solving the mouse_entered and mouse_exited issue in Godot when the mouse is static is to force the engine to continuously evaluate the mouse's position relative to your moving Control nodes. By using _process() or _input() and manually checking for mouse-over conditions, you can ensure that your UI elements respond immediately, regardless of whether the mouse is moving. This ensures a smooth and intuitive user experience for your players. So, go forth and build amazing games, and don't let those pesky static mouse interactions get in your way! Hope this helps, guys!