Debugging & Profiling

Expert guidance for finding and fixing bugs efficiently with Godot's debugging tools.

NEVER Do

• NEVER use print() without descriptive context — print(value) is useless. Use print("Player health:", health) with labels.
• NEVER leave debug prints in release builds — Wrap in if OS.is_debug_build() or use custom DEBUG const. Prints slow down release.
• NEVER ignore push_warning() messages — Warnings indicate potential bugs (null refs, deprecated APIs). Fix them before they become errors.
• NEVER use assert() for runtime validation in release — Asserts are disabled in release builds. Use if not condition: push_error() for runtime checks.
• NEVER profile in debug mode — Debug builds are 5-10x slower. Always profile with release exports or --release flag.

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Available Scripts

MANDATORY: Read the appropriate script before implementing the corresponding pattern.

performance_plotter.gd

Custom Performance monitors for gameplay metrics (projectile/enemy count). Includes automated error state capture with stack traces and memory stats.

debug_overlay.gd

In-game debug UI with real-time FPS, memory, orphan nodes, and custom metrics.

Do NOT Load debug_overlay.gd in release builds - wrap usage in if OS.is_debug_build().

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Print Debugging

# Basic print
print("Value: ", some_value)

# Formatted print
print("Player at %s with health %d" % [position, health])

# Print with caller info
print_debug("Debug info here")

# Warning (non-fatal)
push_warning("This might be a problem")

# Error (non-fatal)
push_error("Something went wrong!")

# Assert (fatal in debug)
assert(health > 0, "Health cannot be negative!")

Breakpoints

Set Breakpoint:

• Click line number gutter in script editor
• Or use breakpoint keyword:

func suspicious_function() -> void:
    breakpoint  # Execution stops here
    var result := calculate_something()

Debugger Panel

Debug → Debugger (Ctrl+Shift+D)

Tabs:

• Stack Trace: Call stack when paused
• Variables: Inspect local/member variables
• Breakpoints: Manage all breakpoints
• Errors: Runtime errors and warnings

Remote Debug

Debug running game:

1. Run project (F5)
2. Debug → Remote Debug → Select running instance
3. Inspect live game state

Common Debugging Patterns

Null Reference

# ❌ Crash: null reference
$NonExistentNode.do_thing()

# ✅ Safe: check first
var node := get_node_or_null("MaybeExists")
if node:
    node.do_thing()

Track State Changes

var _health: int = 100

var health: int:
    get:
        return _health
    set(value):
        print("Health changed: %d → %d" % [_health, value])
        print_stack()  # Show who changed it
        _health = value

Visualize Raycasts

func _draw() -> void:
    if Engine.is_editor_hint():
        draw_line(Vector2.ZERO, ray_direction * ray_length, Color.RED, 2.0)

Debug Draw in 3D

# Use DebugDraw addon or create debug meshes
func debug_draw_sphere(pos: Vector3, radius: float) -> void:
    var mesh := SphereMesh.new()
    mesh.radius = radius
    var instance := MeshInstance3D.new()
    instance.mesh = mesh
    instance.global_position = pos
    add_child(instance)

Error Handling

# Handle file errors
func load_save() -> Dictionary:
    if not FileAccess.file_exists(SAVE_PATH):
        push_warning("No save file found")
        return {}
    
    var file := FileAccess.open(SAVE_PATH, FileAccess.READ)
    if file == null:
        push_error("Failed to open save: %s" % FileAccess.get_open_error())
        return {}
    
    var json := JSON.new()
    var error := json.parse(file.get_as_text())
    if error != OK:
        push_error("JSON parse error: %s" % json.get_error_message())
        return {}
    
    return json.data

Profiler

Debug → Profiler (F3)

Time Profiler

• Shows function execution times
• Identify slow functions
• Target: < 16.67ms per frame (60 FPS)

Monitor

• FPS, physics, memory
• Object count
• Draw calls

Common Performance Issues

Issue: Low FPS

# Check in _process
func _process(delta: float) -> void:
    print(Engine.get_frames_per_second())  # Monitor FPS

Issue: Memory Leaks

# Check with print
func _exit_tree() -> void:
    print("Node freed: ", name)

# Use groups to track
add_to_group("tracked")
print("Active objects: ", get_tree().get_nodes_in_group("tracked").size())

Issue: Orphaned Nodes

# Check for orphans
func check_orphans() -> void:
    print("Orphan nodes: ", Performance.get_monitor(Performance.OBJECT_ORPHAN_NODE_COUNT))

Debug Console

# Runtime debug console
var console_visible := false

func _input(event: InputEvent) -> void:
    if event is InputEventKey and event.keycode == KEY_QUOTELEFT:
        console_visible = not console_visible
        $DebugConsole.visible = console_visible

Best Practices

1. Use Debug Flags

const DEBUG := true

func debug_log(message: String) -> void:
    if DEBUG:
        print("[DEBUG] ", message)

2. Conditional Breakpoints

# Only break on specific condition
if player.health <= 0:
    breakpoint

3. Scene Tree Inspector

Debug → Remote Debug → Inspect scene tree
See live node hierarchy

Reference

• Godot Docs: Debugger

Related

• Master Skill: godot-master