Quick answer: Higher Layer values render on top. Inspect every CanvasLayer in the scene; another one may have a higher layer number than yours. Use conventions (HUD=10, Modal=50, Debug=100) with gaps for insertion.

Here is how to fix Godot CanvasLayer not rendering above UI. You have a game with a HUD on CanvasLayer 1 and a modal popup that should appear over everything — you put it on CanvasLayer 2. The modal shows up underneath the HUD. You raise the modal to layer 5. Still below. You raise to layer 50. Still below. Some other CanvasLayer in your tree has a higher layer number than you realized, and Godot is sorting correctly — your assumption was wrong.

The Symptom

A CanvasLayer with a specific Layer value renders below another CanvasLayer that should be below it. Changing the Layer number does not help until you find a very high number, which suggests some hidden high-layer CanvasLayer is blocking.

Variants: popup renders above HUD but below Pause menu dimmer. Tooltips render behind buttons they annotate. Debug overlay renders under every menu.

What Causes This

Hidden high-layer CanvasLayer. Autoload singletons often contain CanvasLayers for global UI (debug HUDs, screen fade effects, analytics toasts). If one of these is on layer 100 and you thought nothing was above layer 10, your popup at layer 20 is under it.

Parent CanvasLayer overriding. Nested CanvasLayers do not stack; each one starts a new layer at the absolute value. A CanvasLayer inside another CanvasLayer renders at its own Layer value, not relative to the parent.

z_index confused with Layer. Control nodes have z_index for ordering within a CanvasLayer. Setting z_index to 100 on a Control does not override CanvasLayer ordering — it only reorders that Control within its own CanvasLayer.

Viewport node changing order. A SubViewport with its own renderer can produce content that composites in unexpected order with CanvasLayers.

The Fix

Step 1: Audit every CanvasLayer in the scene. In the Scene dock, search for “CanvasLayer” (filter by node type). Check every instance’s Layer property. Include autoloads:

# Print all CanvasLayers and their layer values at runtime
func _ready():
    for node in get_tree().get_nodes_in_group("canvas_layers"):
        print(node.get_path(), " layer=", node.layer)

    # Or find them all:
    _print_canvas_layers(get_tree().root)

func _print_canvas_layers(node: Node):
    if node is CanvasLayer:
        print(node.get_path(), " layer=", node.layer)
    for child in node.get_children():
        _print_canvas_layers(child)

Run this. Output lists every CanvasLayer. Now you know what the actual ordering is.

Step 2: Adopt a layer convention. Document layer numbers across your project:

Gaps let you insert a layer later (e.g. layer 75 for a tooltip above popups but below the overlay fade) without renumbering. Document in CLAUDE.md / README so team members do not pick random numbers.

Step 3: Use Popup nodes for modals. Godot 4 has built-in Popup and AcceptDialog nodes that handle z-ordering automatically via the Window system. Instead of a custom CanvasLayer popup, use:

func show_confirm_dialog():
    var dialog = ConfirmationDialog.new()
    dialog.dialog_text = "Are you sure?"
    dialog.confirmed.connect(_on_confirmed)
    add_child(dialog)
    dialog.popup_centered()

Popup nodes render above all non-popup UI by design. No layer math needed.

Step 4: Diagnose Control ordering within a layer. For ordering within a CanvasLayer (e.g. which Control in a Panel renders on top):

  1. Higher-numbered children in the scene tree render on top
  2. z_index property overrides tree order
  3. Move a Control up/down in the tree to reorder visually

Tooltip Z-Ordering

Tooltips deserve their own high-layer CanvasLayer. A hovered button at layer 10 spawns a tooltip at layer 90. This means tooltips always appear above panels. Combined with mouse_filter = IGNORE so the tooltip does not block clicks on the button.

Performance Note

Each CanvasLayer is a draw batch boundary — Godot flushes the current batch before rendering the next layer. Hundreds of CanvasLayers cost performance. Use layers semantically (HUD, Menu, Tooltip, Debug), not as a per-element z-sort tool.

Understanding the issue

UI is where most player-visible bugs live because UI is what players actually look at. A subtle data bug invisible elsewhere becomes glaring when it produces a wrong label or a stuck button.

The specific bug described above is the kind that surfaces during integration rather than unit testing. It depends on a combination of factors: the asset configuration, the runtime state, the platform's specific behavior. In isolation, each piece looks correct; in combination, the bug emerges. This is why thorough integration testing - playing the actual game in realistic conditions - catches things that automated tests miss.

Why this happens

This bug class disproportionately affects late-stage development. The work to surface it is interactive testing in realistic conditions, which only really happens after the gameplay is in place and assets are populated. Catching it early requires deliberate testing of conditions that look unimportant.

At the engine level, the behavior comes from a deliberate design decision in Godot. The engine team chose a particular trade-off - usually performance versus convenience, or generality versus specificity - and that trade-off has consequences when you push against it. Understanding the trade-off is what turns 'this bug is mysterious' into 'this bug is the expected consequence of this design'.

Verifying the fix

After applying the fix, the verification step has three parts: confirm the original repro is resolved, confirm no obvious regressions in adjacent functionality, and (for shipping titles) deploy to a small player cohort first and watch the crash and report rates. Each step catches something the others miss.

Reproducibility is the prerequisite for verification. If you can't reliably reproduce the bug pre-fix, you can't reliably verify it post-fix. Spend time getting a clean reproduction before you write any fix code. The fix is fast once you understand the reproduction; the reproduction is the slow part.

Variations to watch for

Related bug classes often share the same root cause. If you find yourself fixing this issue, look for cousins: similar symptoms in adjacent systems, the same data flow but a different value, or the same fix pattern in another module. The catalog of 'we've seen this before' becomes valuable institutional knowledge.

Adjacent bugs often share a root cause. After fixing the case you've found, spend an hour searching the codebase for similar patterns. What's the same call with different arguments? The same data flow with a different entity type? The same lifecycle issue in a sibling system? Each match is a candidate for the same fix, or a related fix that prevents future bugs of the same class.

In production

Live games surface this bug class at scale. What's a rare edge case in development becomes a daily occurrence once you have a few thousand concurrent players. The class isn't 'this player has a unique setup'; it's 'one in N thousand sessions will trigger this exact combination'.

When triaging a similar issue in production, prioritize gathering data over hypothesizing causes. A player report describes a symptom; what you need is a build SHA, a session timestamp, and ideally a screen recording or session replay. With those, the bug becomes tractable. Without them, you're guessing at hypothetical reproductions that may not match what the player actually hit.

Performance considerations

Performance implications matter when this bug class scales with player count or asset count. A bug that fires once per session is annoying; a bug that fires once per frame compounds. After fixing, profile the affected code path under realistic load. The fix that's correct for one entity may be too slow for ten thousand.

Diagnostic approach

The diagnostic tools available depend on your engine and platform. Use the engine's native profilers and debug overlays before reaching for external tools. The native tools have context that external tools lack - they know which subsystem owns the code, which assets are loaded, and what state the engine is in.

For Godot-specific diagnostics, the editor's profiler is the canonical starting point. Capture a representative frame with the symptom present; compare against a frame without the symptom; the diff often points directly at the cause. If the symptom is non-deterministic, capture multiple frames and look for the pattern - the cause is usually a state transition or a specific input value rather than a continuous effect.

Tooling and ecosystem

Modern engine versions ship better tooling for this kind of issue than older versions. If you're on an older release, the diagnostic step may take significantly longer because the tools you'd want don't exist yet. Sometimes the right answer is upgrading rather than fighting through limited tooling.

Within Godot, the relevant diagnostic surfaces include the standard frame debugger, memory profiler, and engine-specific debug overlays. Each one shows a different facet of what's happening. The frame debugger reveals draw call ordering and state transitions; the memory profiler shows allocation patterns; the debug overlay reveals per-system state. Bugs that resist one tool usually surrender to another - the trick is knowing which tool to reach for first.

Edge cases and pitfalls

Platform-specific edge cases are worth enumerating explicitly. iOS handles backgrounding differently than Android; Windows handles focus changes differently than macOS. A fix that works on the development platform may not work on every target. Test on each shipping platform deliberately.

When writing a regression test for this fix, focus on the boundary conditions that surfaced the original bug. Tests that exercise the happy path catch obvious regressions; tests that exercise the boundary catch the subtler regressions that look like new bugs but are really the original returning. The latter are the tests that earn their keep over the long life of the project.

Team communication

When this bug class affects multiple teams (often the case for cross-system issues), early communication prevents duplicate work. The team that owns the symptom may not own the cause. A 15-minute conversation at the start of triage often saves hours of independent investigation.

If this fix touches a system several engineers work in, a short writeup in the team's engineering channel helps. Not a full design doc - a paragraph explaining what was wrong, what's fixed, and what to watch for. Future engineers encountering similar symptoms will search for the fix; making it findable is a small investment that pays back later.

“Layer numbers are a global contract. Pick them intentionally, document them, and inspect the whole scene when order feels wrong.”

Related Issues

For SubViewport issues, see Godot SubViewport Texture Blank. For signal issues affecting UI, Godot Await Signal Never Completing covers related patterns.

Audit layers at runtime. Pick a convention with gaps. Popup nodes for modals.