Homing Boulders

In many games which show projectiles, a shortcut often taken by programmers who don't want to bother with complexities such as tracking and physics is to assume that every projectile attack will ultimately "hit" or "miss" its target and dictate this outcome ahead of time, usually with a die roll or Hit Scan trace. Nothing the target can do after that will avoid damage, the projectile follows the target perfectly, often even through obstacles.

This doesn't really cause a problem with lasers and stuff that move too fast for the eye to track anyway, or when attacking a stationary target, but for slower projectiles like medieval arrows, stones and mortar shells—or any case where it otherwise takes a long time for the projectile to actually close the distance—the effect can be quite surreal.

Common symptoms include units taking damage even when the projectile hasn't visibly collided with them (yet), projectiles changing directions (inexplicably, that is) in mid-flight to intercept their target, and so on. Logically, projectiles which are explicitly designed (or enchanted) to home in on their target are exempt from this trope.

Compare Stalactite Spite. See also Roboteching and Hit Scan. Use of this trope may grow less frequent over time as proper physics rendering becomes more advanced, easier to do and expected by players of genres where it was once endemic but at the same time it may be continued as a Retraux touch.

Action Game

 * Spells home in in the video game Harry Potter and the Chamber of Secrets. There's nothing particularly weird about that (after all, a wizard really did do it), but it's made quite clear in the original books that spells travel in a straight line.
 * To further confuse the issue, spells do not home in the Duels.
 * Machinegun bullet streams and lasers in many Gundam games tend to do this as well, but most players don't seem to mind.
 * In particular, the Gundam vs. Series grants better homing abilities to attacks when executed at closer ranges. A couple of the games have a Good Bad Bug wherein one can trick the game into giving the improved homing at any range, giving the player quite literally inhuman accuracy.
 * Noticeable in Prototype when throwing objects at helicopters. Cars, air conditioners, tanks, and people will actually curve to track a moving helicopter if released close enough and the helicopter maneuvers away.
 * Red Dead Redemption allows the player to lock onto targets via Bullet Time, even with thrown weapons. This leads to the often hilarious sight of throwing daggers and sticks of dynamite chasing flying birds like heat-seeking missiles.
 * In Divinity 2 Ego Draconis, bow arrows have a curious tendency to swerve towards you even if you've gotten out of the way, and poisoned arrows are even worse; whereas most magical attacks (which could be justified to home in on you) travel in straight lines and can be sidestepped. In the Orobas Fjords the goblins fire catapults with literal Homing Boulders (they will swerve and seek you out unless you're constantly moving) while Damien's magical ballista towers (which shoot green bolts of energy) shoot in straight, easily dodged lines.
 * Saints Row 2 has a variation, noticeable when using machine guns from aerial locations- despite every bullet being a really, really slow tracer round visually, the game tracks machine guns as Hit Scan weapons. This isn't noticeable when firing at slow targets or at still targets, but when firing at a fast-moving targets, the bullets appear to hit the ground several feet behind the target, which has taken damage from every shot.
 * Left 4 Dead has the Tank, which can rip out chunks of the ground and throw them at the Survivors. The rocks have a degree of homing, but the AI Tanks are even worse to the point where players have nicknamed them "rofl rocks". It doesn't help that AI Tanks can throw rocks that sometimes clip into the level's geometry to reach the player.

Action Adventure

 * An interesting (and literal) example in The Legend of Zelda: Ocarina of Time: In the Death Mountain Trail segment where the volcano erupts, you can move as much as you want and the debris will still fall on your head.

MMORPGs

 * In Maple Story, arrows usually home in on their targets, even if the archer's bow isn't pointing in the same direction. Throwing Stars do funny things, too, but they're Ninja weapons so maybe thats not too surprising...
 * Homing bullets, however, do not have that excuse.
 * Occurs in World of Warcraft. On a fast epic mount, you can fly close to a mob using a ranged attack, and then outfly the mob's projectiles for quite some time if you put some effort into it. The damage gets applied instantly, but it can get hilarious if you fly away for a while and then see the graphics of a bunch of ranged attacks hitting you in succession.
 * The Trope Namer (but not the Ur-Example) is City of Heroes. The damage also isn't applied until the boulder actually hits, although the decision of whether it does is made as soon as its thrown. Hits not only curve and chase you, but will go through walls to impact you. If you aim at a Teleporter, this can lead to some truly amazing boulder throws or sniper shots. Curiously, misses always travel in a straight line.
 * Fortunately this works both ways, as Player Characters can damage enemies with Homing Boulders as well, causing most projectiles to be Fire And Forget.
 * In an interesting counter-trope, a "miss" animation will fly straight, but slightly off-target. No big deal when fighting across a room, but at point blank, this will suddenly cause a projectile to fly straight up or sideways. Alternately humorous, and humiliating.
 * This also occurs in Champions Online. The player character can be teleporting (read: an intangible, invisible mass of energy) and whatever projectiles were launched will pursue you to the point of staying at the exact point where your character is floating. Amusingly, they will not register the hit until after the player completes the teleport.
 * Gigas in Final Fantasy XI toss boulders as a ranged attack. Said boulders travel to their target in a straight line and always hit in the animation, gravity and obstacles be damned.
 * RuneScape is guilty for it, too. Any projectile, when launched, is gonna hit, come hell or high water. If someone throws a knife or fireball at you and you teleport elsewhere before it hits, it will travel to wherever you ended up and connect, no matter how long the distance is. The time is determined by where you were when the projectile was launched, so if you run towards them, it slows down, and if you run away, it speeds up.
 * This used to be true for everything earlier than a certain date. The advent of Corporeal Beast (probably) was also the birth of a ranged attack that targeted a ground location rather than a player, so that players could move away from the location to not get hit - and considering the hit's strength, that was preferable. Many bosses followed suit, having move-dodgeable attacks that target places - but all standard player-targeting missiles or spells will curve to hit their targets.
 * Arrows in Mabinogi have their targets predestined based on which mob you're locked onto; in fact, an arrow can go right through one mob on the way to hit another.

Platform Game

 * The original Spyro the Dragon had this with the cannons in the Peace Keepers and Dream Weavers homeworlds, and the barrels in Gnorc Cove.

Real Time Strategy

 * The arrow examples come from the earlier Age of Empires games.
 * League of Legends has slow moving energy bolts fired by caster minions. Those move only slightly faster than a champion's running speed, follow you anywhere once fired and can do enough damage to kill players on low health even if they've gotten away from them and the enemy team. This is humiliating. Otherwise, some abilities are guaranteed to hit their target while some (known colloquially as "skillshots") require them reaching a target to work. The Flash summoner ability could once be used to dodge homing spells and missiles if used while they were en route, but due to it adding a major benefit to an already useful ability, this was removed.
 * Blizzard's games are notorious for this: StarCraft (at least) feature projectiles which can track a fast enemy all the way across the map- easily 20 or more times the official range of the unit which fired them.
 * Some weapons can miss though. Like in Warcraft 3, Human Mortars, in Starcraft, Terran Siege Tanks.
 * One of the most ridiculous example would be the attack of the Zerg Devourers, a spray of acid that move slower than any other projectile in the game If the Devourer attacks a Carrier's Interceptor (fastest unit in the game) the acid cloud will start orbiting the Carrier, while trailing the interceptor.
 * In the first Mech Commander game, everything homes (including lasers and cannon shells, which move quite slowly and would turn up to ninety degrees to follow a fast-moving Mech) except the short range missiles.
 * AI War Fleet Command, where the projectiles even track the target after it teleports.
 * Company of Heroes has a somewhat interesting duality in this respect. When a unit fires a projectile, it rolls to hit based on the weapon, distance, cover and any other modifiers. If a hit is rolled, the projectile will track the target, which can lead to fairly slow projectiles like bazooka rockets curving mid-flight to follow a fast-moving target. However, if a miss is rolled, the projectile will still be fired in the general direction of the target, with different weapons having different scatter angles. The projectile will then hit the first thing it clips with, whether terrain, obstacles or units. If it hits a unit, it will do damage to that unit in the normal way.
 * Or, even more ludicrously, a shell from a Pak 38 anti-tank gun curving into an M-8 armoured car.
 * In Fallout Tactics, energy weapons travel to their destination slowly enough that the target often has time to duck behind cover. The projectiles do not home, but will still hit the character even if the beam does not connect.

Stealth Based Game

 * Hitman 2: Silent Assassin has an infamous bug in which Agent 47's briefcase can be thrown -- and will slowly but inevitably follow its target around corners and curves before hitting them. It was patched out four months after release, but was then re-instituted as the "Executive Briefcase Mark II" with all its homing flight powers intact.

Turn-Based Strategy

 * In Civilization V, most units don't move a lot during combat animations. Airplanes, on the other hand, are seen moving. Everything makes sense when targeting soldiers equipped with rifles or cities defended by missiles - otherwise, expect arrows, boulders and fire bombs chasing your planes.

Role-Playing Game

 * Happens quite literally in Neverwinter Nights with giants' thrown boulders.
 * Arrows and bolts in the Baldur's Gate and Icewind Dale games will turn midflight to track targets, even if they "miss".
 * Dragon Age does this with arrows (anyone see a pattern?) but the boulders don't track. Just their damage. Which isn't annoying at all.

Notable Aversions

 * In the Total Annihilation series, all projectiles can miss, even the lasers and homing missiles(they can only turn so sharply!). This is actually the main defense of scout/fighter jets, they're just moving too damn fast for most attacks to hit them! Gaining veterancy allows units to lead their targets, but even then, they'll still likely miss the fastest of enemy units.
 * This becomes even more clear when playing around with utterly broken custom units with multiple attacks. There is literally no hitscanning in the game at ALL, not unless you specifically kitbash the game's physics into recognizing it for that particular unit. Two custom units amount to being essentially giant laser shotguns, yet will get torn apart by a fleet of far cheaper PeeWees (tiny machine-gun bots) because there will always be at least a handful in the spread's 'pattern blind spot,' or are missed because in the nanosecond it took to impact their little feet carried them out of the edge of the laser's animation. It makes shmups suddenly not seem so impossible...
 * Command & Conquer had tanks with shells that only have little splash damage. Given how tank shells work in that game, missing the fast-running civilians by one pixel only causes Scratch Damage.
 * The Total War series has archer units, some 200-man strong, and all arrows are animated with ballistic trajectory. You can actually move your camera to watch the volley of arrows fly all the way to the target. They do not always hit, of course. Also the trajectory means that arrows can hit friendly units in the back if they are in the way, although archers usually fire upwards over the heads of friendly units when necessary.
 * Can be particularly impressive when watching five or six archer units - totaling out to sometimes more than a thousand men - firing arrows at a fleeing unit. You'll see hundreds of individual arrows screaming down at the retreating enemy, and it becomes even more awesome if you have them all on fire.
 * The Myth series is another notable example of free-flying projectile physics, (in)famous for the horribly messy friendly fire caused by only somewhat accurately aimed arrows, spears, and high explosives arcing over the terrain and interacting unpredictably with objects.
 * In Bloodline Champions, if it can harm your enemy in some way... it will never do this. Even standard healing abilities require a bit of aim, and only some effects that are friendly and targetted to one person will always hit. Yes, that taunt ability has to travel and make contact with an enemy.