RUST BUSTERS: The Ring, the Red Circle and the Roll

Two arcade ideas on one cover line

CABAL, released by TAD Corporation in 1988, shows the battlefield from behind the player: you move a soldier along the bottom of the screen, aim a separate crosshair, roll to dodge, knock down buildings and empty an enemy gauge to clear each screen. Virtua Cop, SEGA's 1994 light-gun shooter, drew its world in 3D polygons, put a lock-on marker that shrinks on any enemy about to fire, and sent civilians into the line of fire.

RUST BUSTERS keeps both habits. The commando stands on a cover line 8 m wide and only moves left and right; the crosshair goes wherever the mouse, a finger or the right stick puts it. Each of the five stages has two areas that end when the ENEMY gauge is empty — 26 to 40 points alone, where a basic robot is worth 1 and a tank 6 — and a third area with a boss. The rule I changed most is the ending of the ring: when it closes you are not hit yet. The robot launches a bolt you can see, and every heavier attack draws a warning of its own.

The ring and the bolt behind it

A ring appears over a robot that starts aiming and narrows as its timer runs, green at first, yellow after 45% and red after 75%. When you are the target it is drawn thicker and brighter, fills red at the end, and a charging sound plays. The timer is 1.6 s on stage 1, then 1.34, 1.23, 1.12 and 1.01 s on stage 5.

Three things stop or delay a shot. A robot destroyed before its ring closes never fires. A hit on a robot that is aiming moves its timer back 0.22 s, twice at most; tanks and bosses ignore this. And a robot whose cover is broken drops its aim and walks to a new spot.

Once fired, a bolt flies at 17.5 m/s on stage 1, rising to 25.1 m/s on stage 5, toward a point fixed at that moment, and it hurts only if you are within 0.46 m of that point when it arrives. Robots aim where you would be 0.2 to 0.55 s later if you kept moving, plus a small random error, so the dependable answer is to stop or turn back as the ring goes red. From a standstill the commando covers 0.92 m in about 0.27 s. Holding fire slows walking to 72%, so let go for the step.

Red circles on the ground

Grenades, shells and missiles land on the cover line inside a red circle, and the circle is exactly the area that hurts: the blast radius plus half the commando's width. A disc inside it fills as the moment of impact approaches. Grenade robots lob at where you will be 0.35 s later; the grenade takes 1.15 s and covers 1.68 m either side. Rocket drones fire missiles with a smoke trail that take 2.35 s and cover 1.48 m.

Grenades and missiles can be shot out of the air for NICE SHOT! and 200 points. Shells cannot be shot. A tank fires two: one on your position that lands after 1.45 s and one 1.9 m to a random side after 1.75 s, each covering 1.73 m, so clear both circles. SCRAP CRAWLER fires volleys of three shells, later five, 0.26 s apart: on your position, then 2.1 m to each side, then 3.8 m to each side. Measured with an automatic player over 80 runs (8 per stage, alone and in pairs), shells caused 294 of the 635 hits taken, more than any other attack.

Bands: shockwaves, beams and sweeps

A shockwave is a bright band that slides along the ground from a boss to your line. It covers the entire line, so there is nowhere to walk to. Roll instead: a roll is invincible from 0.03 to 0.42 s after you press, carries you about 3.2 m and cannot be repeated for 0.78 s from its start. The waves travel at about 13 to 16.5 m/s, so that window covers 5 to 6.4 m of their path; press when the band is a few metres away, not at the last instant. Double stomps from IRON STOMPER and LEGION TITAN send two waves 0.7 s apart, TWIN BASTION's pulse two 0.9 s apart.

A beam starts as a red band 1.7 m wide that flashes on the line for 1.1 s, then becomes a column of light for 0.55 s. Leave the band while it flashes; a roll also takes you clear. TWIN BASTION's core fires three beams 0.75 s apart, and LEGION TITAN's eye beam sweeps across four spots 0.42 s apart with a shorter 0.95 s warning, skipping one of them.

A sweep is a row of bolts, one every 0.72 m across the whole line, fired 0.1 s apart from one end to the other. The bolts within 0.85 m of one random point are left out. SCRAP CRAWLER and SKY HAMMER both use it: stand on that point, or roll through the row. SKY HAMMER's bombs follow the same idea with shells — four slots across the line, one of them empty.

Cover that breaks

Every prop has health, and the pistol does 1 damage per shot. Sandbags take 9, concrete barriers 14, a wooden crate 4, a watchtower 26, a bunker 32 and a container 40. Destroyed props fill the ENEMY gauge as well: 3 for a watchtower or bunker, 2 for a fuel tank, container or radio tower, 1 for a tent, car, van or generator. Some towers and bunkers carry a turret that fires two-shot bursts; when the structure falls, the turret goes with it and adds 2 more.

Some robots crouch behind cover and rise to shoot. While they are down your shots strike the prop, and the touch aim assist ignores any robot more than 60% hidden. Break the cover and the robot is in the open.

Explosive barrels take only 2 damage and blow up over 3.4 m, hitting robots and setting off other props in reach; cars, vans, fuel tanks and generators explode too, over 2.8 to 4.6 m. Explosions also detonate grenades and missiles in flight. They never hurt civilians — only bullets do. A civilian you shoot costs 1,000 points and a heart, even while you are still blinking from a hit. One who gets across unhurt pays 500 to each player and, 40% of the time, drops a medkit or grenades.

Weapons and pickups

The Pistol never runs out: 12 rounds, 0.16 s between shots, 0.95 s to reload. Special weapons come from items. The Machine gun has 140 rounds at 0.085 s apart, about 12 s of held fire, for 0.8 damage each; the Shotgun has 18 shells of eight pellets at 0.7, one every 0.5 s; the Grenade launcher has nine rounds that do 7 blast damage over 3.1 m. Hand grenades start at 2, stack to 5 and do 11 over 4.2 m.

Items are collected by shooting them, and they vanish 9 s after landing. Every battle area and four of the five boss areas have a crate holding a fixed weapon, a supply crate falls by parachute every 20 to 34 s depending on the area, and robots and props drop the rest. Picking up the weapon you already carry adds its ammo, up to twice the normal load, while a different one replaces it. A medkit restores 2 hearts, or goes to a hurt partner if you are full, a medal is worth 1,000, and every pickup adds 300.

Five bosses and their weak points

Bosses take 55% of the damage from bullets on the body (TWIN BASTION 50%), while explosions hit the body at about full strength, and they carry weak points shown as glowing yellow spheres with diamond markers. Below two thirds and one third of their health they move to harder attack sets and ignore damage for 1.1 s; most also call in robots at that moment. Against the 55% body rate, a ×2.2 weak point does four times as much per bullet.

• SCRAP CRAWLER, Jungle Outpost, 230 HP — hatch ×2.2, cannon ×1.5. Shell volleys, bolt bursts and sweeps.
• SKY HAMMER, Downtown Avenue, 260 HP — two engines with 60 HP each (×1.4) and the cockpit (×2.0). Breaking both engines sends it into its last phase, flying lower. Strafing sweeps, missiles, bombs and drones.
• IRON STOMPER, Container Harbor, 290 HP — core ×2.4, arm cannon ×1.3. Stomps, beams, missiles and grenade robots.
• TWIN BASTION, Red Canyon Base, 290 HP — two cannons with 90 HP each; the core (×2.0) stays shielded until both fall. Alternating shells and crossfire, then core beams and pulses.
• LEGION TITAN, Legion Fortress, 380 HP, 10.4 m tall — head ×2.2, chest core ×1.6. Punches, eye-beam sweeps, double stomps, shell volleys, and it can summon a heavy robot.

Playing as two

The host can deploy alone and the friend can drop in later, arriving with 2.5 s of invincibility. With two commandos, the field holds 1.6 times as many robots, new ones appear 0.68 times as far apart, and one more robot may aim at once — two more from stage 4. These apply the moment the friend arrives. The ENEMY gauge (×1.5) and boss health, weak parts included (×1.6), are set when an area begins, so someone joining halfway does not lengthen the area you are in.

Every robot picks a random living commando to aim at. A downed player stands up after 6 s with 3 hearts as long as the partner is alive; if both go down, the continue screen appears. Items belong to whoever shoots them, rescued civilians pay both players, and the result screen names the higher scorer 'Ace of the mission'. Three stars use the average of both players' hits.

The server runs the same rules at 30 Hz and sends positions 15 times a second. A shot is judged by the shooter's own screen; the server checks only ammo, fire rate and that the target is alive. For a co-op game I put responsive shooting ahead of cheat-proofing. Measured with the automatic player at skill 0.55, a stage took 129 to 210 s of fighting alone and 112 to 185 s as a pair.

Controls built for thumbs

On a phone you tap the field where you want to shoot, and a finger kept down keeps firing while you slide it to aim. A tap that touches no robot, prop or item is moved to the nearest robot, item or incoming grenade or missile within 34 px, reaching slightly farther for robots that are aiming. Civilians are never picked this way, and on a boss the assist lands on the body, so aim straight at the diamonds. The mouse gets 7 px and a gamepad 24 px, and the gamepad crosshair slows to 40% within 40 px of a robot.

The left thumb uses a floating stick: touch anywhere in the lower-left part of the screen, 52% of its width and 30% of its height, and the stick appears under it. The Roll button, the largest at 78 px, sits at the bottom right with the Grenade button beside it and the weapon panel above, which reloads the pistol or switches weapons. A roll goes the way the stick is pushed, or the way you face; a grenade goes where you last tapped.