What causes a mahjong tile not being flagged free when a side is open?

The free-tile check requires both the left and right neighbors to be empty instead of either one, so tiles with only one open side are incorrectly treated as blocked.

How do I catch this when it only happens for some players?

Capture it automatically from the player's device with the full stack trace, the device and OS, the build, and a breadcrumb trail of what they did. That turns a vague complaint into a specific, reproducible issue you can fix without owning the hardware it happens on.

How to Fix a Mahjong Tile Not Being Flagged Free When a Side Is Open

Quick answer: Mark a tile selectable when nothing covers it from the layer above AND at least one of its left or right horizontal neighbors is clear.

In mahjong solitaire a tile is free if it has no tile on top of it and is open on its left or right side. Requiring both sides open wrongly locks many playable tiles. Use OR for the horizontal sides.

How to fix it

1. Check the layer above first

A tile is blocked if any tile in the layer above overlaps its footprint. Compute overlap using the half-cell offsets mahjong layouts use, not exact cell equality.

2. Use OR for left and right

If nothing is on top, the tile is free when its left side is clear OR its right side is clear. Only when both horizontal sides are occupied is it blocked.

3. Recompute free state after each removal

Removing a pair can free previously blocked tiles. Re-evaluate the free set after every match so the player always sees current selectable tiles.

Catching the ones you can't reproduce

The hardest version of this to fix is the one you can't reproduce — it only happens on a player's hardware, OS, driver, or save state, under conditions that simply aren't present on your machine. A report that says “it crashed” or “it froze” gives you nothing to act on, so the bug survives release after release while quietly costing you players.

Automatic error capture closes that gap. Each failure arrives with its full stack trace, the device and OS, the build number, and a breadcrumb trail of what the player did right before it broke, so even a failure you have never seen becomes a specific, reproducible issue. Fold identical failures into one signature ranked by how many players each hits, and your worklist sorts itself worst-first instead of arriving as a stream of vague complaints.

This is where a tool like Bugnet earns its place. Its SDK captures every HTML5 error automatically with the full stack trace plus device, OS, memory, build, and game-state context, folds duplicates into one grouped issue with an occurrence count, and ties each to the build it first appeared on — so you fix the problem that hurts the most players first and confirm it is gone when its signature disappears from the next release.

Reproduce it once with full context and the fix writes itself. The hunt is the expensive part.