How to Implement Line of Sight

Line of sight—whether one position can see another—is a fundamental query underpinning AI perception, stealth, fog of war, and many other mechanics. Understanding how to compute it efficiently and use it well is essential for any game where what characters can and can't see matters.

Raycasting answers the visibility question

The core of line of sight is determining whether the straight path between two points is unobstructed: can an enemy at A see the player at B, or does a wall block the view? The standard technique is raycasting—conceptually shooting a ray from one point toward the other and checking whether it hits any obstacle before reaching the destination. If nothing blocks it, there's line of sight; if something intervenes, there isn't. This simple query is remarkably powerful, answering the visibility question that so many mechanics depend on, and most engines provide raycasting against the collision world, making line-of-sight checks straightforward to implement. The result—a clear yes or no on whether two points can see each other—is the building block for perception and visibility systems throughout a game.

Line of sight underpins AI perception, stealth, and visibility mechanics, but it needs thoughtful use. For AI, line of sight is the basis of perception—an enemy can react to the player only if it has line of sight, which makes stealth possible (break line of sight to hide) and makes AI feel fair (enemies see what they realistically could). For stealth specifically, line of sight combined with facing and range determines whether the player is detected, the core mechanic of sneaking. For fog of war and visibility, line of sight determines what the player can see, revealing and hiding the world based on what's in view. Using line of sight well means more than the raw query, though: AI perception usually combines line of sight with field of view (enemies don't see behind them) and range (they don't see infinitely far), and performance matters since checking line of sight for many agents every frame adds up, so you check it judiciously rather than constantly. Built on raycasting and used thoughtfully—combined with facing and range, computed efficiently—line of sight provides the visibility foundation that perception, stealth, and fog-of-war mechanics all rest on, which is why it's one of the most fundamental queries in game programming.

Let real players be the judge

It's remarkable how differently real players behave from how you imagine they will. The tutorial you think is obvious confuses them; the feature you agonised over goes unnoticed; the thing you almost cut becomes their favourite. None of that is visible from inside your own head, which is why watching real people play is the single highest-leverage thing most developers under-do.

Watch without intervening, resist the urge to explain, and pay attention to what players do as much as what they say. Their confusion and their choices are data, and acting on that data is what turns a game that works for you into one that works for everyone.

Polish where players actually look

Polish is not evenly valuable. Players form an impression in the first minutes and spend most of their time in the core loop, so effort spent there returns far more than effort spread thin across content few people reach. The opening, the moment-to-moment feel, and the things every player touches are where polish converts directly into how good the game feels.

Be deliberate about it. Make the first impression strong and the core interactions satisfying before widening out, because a great core with less content almost always beats a sprawling game that never feels good to play.

Scope is a decision, not an accident

Almost every overscoped game got that way one reasonable addition at a time, with no single decision ever feeling like the mistake. The finish line recedes a little with each new feature, and because the project always feels nearly done, the developer rarely notices how far the goal has drifted until they're exhausted and the game still isn't out.

Treat scope as something you actively decide rather than something that happens to you. Write down what the finished game contains, make every addition a conscious trade against that, and keep most new ideas in a backlog where they belong — because a small game you finish beats a large one you abandon.

Measure before you optimise

Intuition about what's slow, what's confusing, or what's driving players away is usually wrong, and acting on it wastes effort on problems that don't matter while the real ones persist. The developers who improve their games efficiently are the ones who measure first — profiling performance, watching real sessions, capturing actual errors — and let the data set their priorities.

It's slower than trusting your gut, but it's the only approach that reliably improves the game instead of just changing it. Find the biggest real problem, fix that, and measure again, rather than optimising guesses.

The first impression is most of the battle

More players leave in the opening minutes than at any other point, which makes the first few minutes the highest-leverage stretch of the whole game — and also the part the developer can least see clearly, having played it a thousand times. What feels obvious to you is often confusing to someone seeing it fresh, and that gap quietly costs you players before they ever reach the good part.

Get the player into the interesting part fast, let them feel competent quickly, and watch first-time players go through the opening without helping them. Nobody quits a game they're enjoying, so making the early minutes land is most of the battle for retention.

Line of sight checks whether anything blocks the path between two points, usually by raycasting. It underpins AI, stealth, and fog of war.