Fix: Godot CharacterBody2D move_and_slide Ghost Collision

Here is how to fix Godot 4 CharacterBody2D bodies that snag on otherwise flat ground. The character runs smoothly across a TileMap floor until it suddenly stops dead at a perfectly flat seam between two tiles. Or it bounces a few pixels into the air every time it crosses a tile boundary on a slope. Both problems share the same root cause: rectangular colliders meeting a stack of independent tile collision shapes.

The Symptom

Movement looks correct in the Scene view but the running character occasionally hitches, stops, or pops upward when crossing TileMap seams. Smooth ground feels lumpy. On slopes, the character may briefly leave the ground at every tile boundary, breaking is_on_floor() checks and triggering false “in air” animation states.

What Causes This

Rectangular collider on the character. A RectangleShape2D has sharp corners. When moving over a tile-tile seam, the leading bottom corner can catch the rising edge of the next tile’s collision shape (even if visually they line up perfectly).

Independent per-tile collisions. TileMap collisions are built per cell. Adjacent floor tiles each contribute their own shape; numerical precision makes the seam slightly imperfect.

safe_margin too small. The default of 0.08 px is fine for most cases but tiny on tilemaps with subpixel-precise placement. Raising it gives the engine more slack to resolve seams correctly.

floor_snap_length disabled. Without it, the character physically leaves the ground for one frame at every minor bump, breaking continuous floor contact.

The Fix

Step 1: Use a CapsuleShape2D. Replace the RectangleShape2D on the CollisionShape2D with a Capsule. Set the capsule’s radius to half the character width and height to roughly the character height. Rounded bottom edges roll over tile seams instead of catching them.

Step 2: Tune CharacterBody2D properties.

extends CharacterBody2D

const SPEED := 200.0

func _ready():
    floor_snap_length = 8.0     # Glue to floor across small gaps
    floor_max_angle = deg_to_rad(50)
    safe_margin = 0.1           # Default 0.08 -> 0.1
    slide_on_ceiling = true
    max_slides = 4              # Default already 4, set explicitly

func _physics_process(delta: float):
    var dir = Input.get_axis("left", "right")
    velocity.x = dir * SPEED
    velocity.y += 980.0 * delta
    move_and_slide()

Step 3: Merge TileMap collisions where possible. Open the TileSet, select your floor tiles, and ensure the Physics layer collision polygons are identical and span the full tile. Where you have long stretches of identical floor, consider replacing TileMap collisions with a single StaticBody2D that has one wide CollisionShape2D — no seams, no problem.

Step 4: Use floor_constant_speed. When walking up gentle slopes, the default behavior reduces horizontal speed by the cosine of the slope angle. Setting floor_constant_speed = true keeps horizontal movement constant regardless of slope, which feels better and avoids small per-frame velocity changes that interact badly with seams.

Step 5: Verify with the collision debugger. Run the project, enable Debug → Visible Collision Shapes. Move slowly across a problem seam. If you see the character collider catching on a corner, you have visual confirmation. Adjusting capsule radius, safe_margin, or merging tile collisions should resolve it.

When You Cannot Use a Capsule

Some games need a rectangular hitbox for gameplay reasons (pixel-art platformer with strict bounds). In that case, use a separate CollisionShape2D for movement (capsule) and another for gameplay (rectangle), with the rectangle on a different collision layer that only the gameplay queries use.

# Movement collider (capsule, layer 1)
$MovementShape.shape = CapsuleShape2D.new()

# Hitbox (rectangle, layer 2 only)
$HitArea.collision_layer = 2
$HitArea.collision_mask = 2

Understanding the issue

This bug class falls into a pattern that's worth understanding beyond the specific case. In Godot Engine, the underlying behavior is shaped by how the engine layers its abstractions - the public API you call, the runtime systems that respond, and the platform-specific implementations underneath. A bug at any layer can produce symptoms that look like they originate at a different layer. Triaging effectively means recognizing which layer the symptom belongs to, even when the gameplay code is what's visible.

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

For shipping games, the safest verification is a staged rollout. Apply the fix to 1% of players for 24 hours; watch the affected metric; expand if green. Skipping the staged rollout means the verification is the entire player base, which is too high a stakes for most fixes.

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

There's almost always a less obvious case where the same problem applies. The reported case is the one a player hit; the related cases hide because they're rarer or affect fewer players. After fixing the reported case, search the codebase for the pattern - one fix often unlocks several.

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

In shipping builds, this issue may interact with other production-only behavior. Stripping, encryption, asset bundling, and platform-specific code paths can each modify the symptoms. When players report a related issue, capture build SHA, platform, and any feature flags - those three fields cover most of the production-only variations.

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

Before applying any fix, gather enough context to be confident you're addressing the actual cause and not a similar-looking symptom. The cheapest diagnostic step is reproducing the bug deterministically - if you can't get the same failure twice in a row, your fix attempts will be hard to evaluate. Lock down the reproduction first.

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

The tooling around this bug class matters as much as the fix itself. Good logging, accessible profilers, and clear error messages turn 30-minute investigations into 5-minute ones. If your project doesn't have visibility into this code path, the first fix should add the visibility - the second fix uses it.

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

Document the fix and its rationale in the commit message or attached engineering doc. Future engineers will encounter related issues; the rationale tells them whether your fix is reusable or specific to the case at hand. Without rationale, the fix gets reverted or copied incorrectly.

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.

“Capsule colliders roll over seams. Rectangles catch them. Choose your weapon.”

Related Issues

For floor snap problems specifically, see CharacterBody2D Floor Snap. For collision shape disable issues, see CollisionShape Disabled Not Re-Enabling.

Round the bottom. Raise the margin. Snap to floor. The seams disappear.