Arena Shooter

How to play

You steer a small combat drone in a walled arena seen from above. Robots arrive in waves through spawn pads around the edge: a growing ring shows where one is about to appear, and arrows at the edge of the screen point to robots you cannot see yet. Destroy every robot to clear the wave, then choose one of three upgrades. Each new wave brings more robots that move faster and shoot more often.

Your drone has 6 health points on Easy, 5 on Normal and 4 on Hard. Each hit costs one, and the drone is protected for a moment afterwards. Every fifth wave a large Sentinel boss arrives with ring blasts, spiral streams and robots of its own; after each boss the arena changes its layout. Your best score for each mode stays in your browser and is not uploaded.

The robots

• Chaser (red arrowhead): runs straight at you and breaks up on impact.
• Shooter (violet square): keeps its distance, circles you and fires a slow orange bolt after a short charge.
• Splitter (green circle): slow and tough; it bursts into three fast splinters.
• Dasher (yellow diamond): stops, draws a dashed line and charges along it, so step aside.
• Tank (orange, with tracks): slow and heavily armoured; fires three bolts in a fan.

Destroyed robots sometimes drop a power-up for 10 seconds: rapid fire (double rate), spread shot (three bullets in a fan), speed (35 % faster) or a shield (7 seconds of protection that also lets you ram small robots).

Controls

• Mouse and keyboard: W A S D move, the cross-hair follows the mouse, hold the left button to fire.
• Keyboard only: the arrow keys aim in eight directions and Space fires. The gun locks on to a robot within 12° of the arrow direction.
• Touch: put your left thumb anywhere on the left half and drag to move; drag on the right half to aim and fire. On touch the gun locks on within 8°. The page does not scroll while you play.
• Auto-fire (button or T) keeps the gun firing, so you only steer and aim.
• P or Esc pauses, M switches sound, F toggles full screen, 1 2 3 pick an upgrade. Switching tabs pauses the game.

How it works

Vectors for moving and aiming

The movement keys give a direction vector. Pressing W and D together gives (1, −1), which is √2 ≈ 1.41 times longer than a single key, so the game divides by the length: diagonal movement is exactly as fast as straight movement. The drone does not jump to full speed: it speeds up at 3000 and brakes at 3600 units per second squared, so from its top speed of 290 units per second it stops about 0.08 seconds and 11 units after you let go. The aim angle is

θ = atan2(y_target − y_drone, x_target − x_drone)
bullet velocity = 950 · (cos θ, sin θ)

Collisions

Every robot, bullet and the drone is a circle, so a hit is a distance check: two circles touch when the distance between their centres is smaller than the sum of their radii. Walls are rectangles: clamping the circle's centre to the rectangle gives the closest point, and the circle is pushed out along that direction, so you slide along walls instead of sticking.

Finding a way around walls

The arena is split into a grid of 50 by 50 unit cells. Ten times a second the game runs Dijkstra's algorithm from your cell and stores the distance from every free cell to you (a straight step costs 1, a diagonal step √2). A robot that cannot see you moves to the neighbouring cell with the smallest distance, which always leads around the walls; with a clear line of sight it heads straight for you.

Leading the target

A shooter does not aim at where you are but partly at where you will be. With your velocity v, its distance d and bolt speed s, it aims at

aim point = your position + k · v · d / s

where k grows from 0 in the first waves to 0.5, plus 0.1 on Hard. Because it only partly leads and never guesses a turn, changing direction just after it fires makes it miss. Robots, including the boss, only start an attack once they are on your screen.

Things to try

• Use the walls as cover: shooters and tanks only fire with a clear line of sight.
• Combine Twin barrel with Spread shot for a wall of bullets.
• Hit a splitter from far away so its splinters have a long way to run.
• Try a whole run with auto-fire on and concentrate only on dodging.
• Watch a dasher's dashed line and step to the side just before it charges.

Frequently asked questions

Does the game ever end?

No. Robot speed and fire rate stop rising after a while, but waves keep getting bigger until the robots win.

Which upgrade is best?

Fire rate and damage add up the fastest. Field repair only appears when you are damaged, and Armor plating adds one more hit point.

Can I play with a keyboard only?

Yes. W A S D move, the arrow keys aim with a small lock-on, and Space or auto-fire shoots.