Does Set Tile update collision in Construct 3?

Yes — the Tilemap’s Set Tile action invalidates the collision mesh for that tile and rebuilds it. If your collision still feels wrong after Set Tile, the issue is probably elsewhere: the colliding object using cached collision data, or the tilemap’s collision polygons being defined incorrectly in the tileset editor.

Why does my object still pass through a tile I removed?

Most likely the colliding object is moved by behavior (Solid, Platform) that resolves collisions on its own update. Place the Set Tile action before any movement check in the event order. If the object was in the middle of a tile when it was removed, it may now be inside the new empty tile but with momentum carrying it through — this is correct behavior.

How do I set tile collision polygons?

In the Tilemap project file’s Tileset editor, click a tile and use the Collision Polygon tool. Draw the shape that should be solid for that tile. Each tile can have its own polygon, allowing slopes and irregular shapes. The default is a full bounding box.

Fix: Construct 3 Tilemap Collision Mesh Not Updating

Quick answer: Tilemap.Set Tile already updates collision — if it still feels wrong, audit per-tile collision polygons in the tileset editor and check event order so Set Tile runs before movement resolution.

You destroy a destructible tile in mid-air. The player should fall through the now-empty space — instead, they stand on what looks like nothing. The visual updates instantly but the collision behaves as if the tile is still there.

How Tilemap Collision Updates

Construct 3’s Tilemap plugin maintains an internal collision mesh derived from each tile’s collision polygon. When you call the Set Tile action, the engine:

Updates the tile id at the target cell.
Invalidates the collision shape for that cell.
Recomputes the shape from the new tile’s polygon on next collision query.

Set Tile is intentionally cheap; the recomputation is lazy. By the next physics step, the new layout should be authoritative.

If Collision Still Looks Wrong

Cause 1: Event order

If your event sheet does:

1. Every tick: Player Platform Behavior simulates control
2. On condition X: Tilemap Set Tile (cell, -1)

The platform behavior already resolved collisions for this frame using the old tile layout. The Set Tile happens, but the player’s position for this frame is already determined. Next frame, collision is correct, but for one tick the player stands on an empty cell.

Move the Set Tile action above the movement-resolving events — or trigger it from input handling before behavior updates.

Cause 2: Per-tile collision polygon

Open the tilemap’s tileset. For each tile, the Inspector shows a Collision Polygon. If a tile shows the default rectangle but should be empty, the tile is solid even though the art is just a decoration. Click the tile and:

To make it pass-through, set the polygon to empty (delete all points).
For a slope, draw a triangle.
For a one-way platform, draw only the top edge.

Cause 3: Behavior caching

The Platform behavior caches the platform it’s standing on between frames for stability. After destroying the tile under the player, the behavior may need one frame to notice. This is by design and usually invisible; if it bothers you, manually call Player.Platform.SetVectorY(1) after destroying the tile to nudge it off the cached platform.

Verifying

Open Project Properties → Show debug info and run the layout. The debug overlay draws collision polygons on tilemap cells. Watch the polygons disappear as you Set Tile to -1 (empty). If a polygon stays visible after the tile is gone, the action isn’t reaching the tilemap (wrong instance reference, or the call was conditional and didn’t fire).

For Procedural Tilemaps

When generating tilemap data at runtime (e.g., from a noise function):

// Pseudo-code in event flow
For each X, Y in level bounds
    Tilemap Set tile (X, Y) to tile_for_height(X, Y)

Each Set Tile invalidates that cell’s collision. For very large tilemaps generated in a single tick, you can hit a perceptible frame hitch — spread the generation across multiple ticks using a counter and yielding back to the engine.

Understanding the issue

Tilemaps are dense data structures. A single tile change touches several other systems: rendering, collision, possibly navigation. Bugs at the intersection often look like 'I changed one tile, why did three other things break'.

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

The triage path for this kind of bug is long. The symptom appears in gameplay, but the cause is in a different system. The reporter describes the gameplay effect; the engineer has to translate that into a hypothesis about the underlying cause. Misdirection is common.

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

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

If this issue manifests under high load (many actors, many particles, many network connections), profile the post-fix code path with realistic counts. The original cost was a bug; the new cost is real work, and real work has a budget.

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

Third-party plugins often provide better diagnostics for their own behavior than the engine does. If the affected code is in a plugin, check the plugin's documentation for debug modes, verbose logging, or inspector tools - these can save hours of investigation when they exist.

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.

“Set Tile updates collision. The bug is almost always in event order or per-tile polygon definitions.”

Enable “Show debug info” while developing — you can see collision polygons live, which makes most tilemap bugs obvious.