Fix: Construct 3 Sprite Mirror Flips Collision Box

Your player has a sword sticking out to the right with a collision polygon extending into the blade. The player turns left (Mirror); the sword visually points left as intended; but enemies on the player’s right side now take damage because the collision polygon also flipped and reaches into space behind the player.

Mirror Affects Both Visual and Collision

Mirror is a transform-level flip on the sprite. The same transform applies to the rendered image and to the collision polygon — they’re both expressed in the sprite’s local space and rendered through the same matrix. There’s no per-property control to mirror visual but not collision (or vice versa).

For most cases this is what you want: an asymmetric character with a tail on the right should have a collision shape that puts the tail on the left when mirrored. The bug pattern is specifically asymmetric attack hitboxes — where you intend the collision to follow your attack direction, but the same direction must come from explicit facing logic, not the visual mirror.

Fix 1: Symmetric Collision Polygon

If the character’s body collision should be the same regardless of facing direction:

1. Open the sprite in the Animation editor.
2. Edit the collision polygon to be symmetric about the vertical axis.
3. Save.

A common shape is an oval or hexagon centered on the origin. Mirroring this leaves it unchanged. Players and enemies use symmetric body hitboxes; only attack-specific hitboxes need facing-aware logic.

Fix 2: Separate Hitbox Sprite for Attacks

For melee attacks where the hitbox should reach a specific direction:

1. Create a new sprite HitboxSword with the desired collision polygon and invisible image.
2. Pin it to the player on attack start.
3. Position offset based on facing: HitboxSword.X = Player.X + 24 * (Player.Mirrored ? -1 : 1).
4. Destroy after the attack animation finishes.

The hitbox sprite isn’t mirrored — only its position offset changes with facing. Collision behaves as expected: hitbox is on the right when facing right, on the left when facing left.

This pattern also lets you have multiple hitboxes per attack (e.g., a swing arc), spawn them at specific animation frames via the Sprite’s “On frame changed” trigger, and tune their lifetime independently of the visual.

Fix 3: Facing Variable Instead of Mirror

Some teams use an instance variable facing (1 or -1) instead of Mirror. Visual flipping is done via Sprite.SetScale(facing, 1) or via two-direction sprites. Collision polygons must be drawn symmetric in the editor, but you have full control over hitbox positioning since the runtime never “mirrors” anything.

Diagnosing

Enable the debug overlay with the Inspector’s “Show debug info”. Press F12 in the runtime preview and select your sprite — the collision polygon is drawn over the sprite. Mirror the sprite (Set Mirrored On) and watch the polygon flip. That’s the moment to decide: symmetric polygon, separate hitbox, or facing-variable architecture.

Verifying

Build a test layout with the player facing both directions, swinging the sword at static targets on both sides. Targets should only take damage from the side the sword is pointing at. Stale-hit reports usually indicate a missing facing check or an over-large collision polygon.

Understanding the issue

This bug class falls into a pattern that's worth understanding beyond the specific case. In Construct 3, 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

Bugs of this class are particularly easy to ship past internal QA because they often depend on specific runtime conditions - hardware combinations, network states, or asset configurations that QA didn't reproduce. Players hit them in the wild, file reports that are hard to repro, and the bug accumulates negative reviews while engineering tries to recreate the failure mode.

At the engine level, the behavior comes from a deliberate design decision in Construct 3. 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

Verifying this fix in isolation is straightforward: reproduce the bug, apply the change, confirm the bug no longer reproduces. The harder verification is regression - did this fix introduce a new bug elsewhere? Run your standard regression suite, plus any tests that exercise the same code path with different inputs.

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

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

Diagnosing this class of bug benefits from a structured approach: confirm the symptom, isolate the variables, hypothesize the cause, and verify the hypothesis before writing fix code. Skipping the isolation step is the most common mistake; without it, fixes often address symptoms while the underlying cause continues to produce other variations.

For Construct 3-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 Construct 3, 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

Boundary conditions deserve specific testing attention. What happens when the input is zero, maximum, negative, or NaN? What happens at the start of a session vs hours in? What happens at the boundary between two systems handling the same data? These are where bugs hide and where regression tests are most valuable.

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.

“If the hitbox should reach a specific direction, the hitbox is its own sprite. Don’t fight the mirror; sidestep it.”

Hitbox-per-attack also makes balance changes easier — tune one hitbox without touching player art.