Parallaxian: Good Morning Aviators!!!

1 March 2023 · Updated 26 February 2026

Been putting the Hunter-Killer drones through their paces in what I’ve dubbed “Drone Alley” — a stripped-down test environment where I can throw wave after wave of HKs at the player without any of the scrolling, ground targets or mission objectives getting in the way. Just you, your guns, and a sky full of angry drones.

Colour-Coded Hostility

The HKs use a colour progression to telegraph their aggression level. They start out green — relatively docile, predictable flight paths, the kind of thing you’d swat away without breaking a sweat. As your kill count rises, survivors start cycling through yellow, orange, red and eventually black. Black HKs are absolute psychopaths. They don’t just fly at you — they actively manoeuvre to get behind your tail and pour fire into your six o’clock. They’ll try to ram you if they can’t get a clean shot. The sprite colour change is trivially cheap — just an STA $D027,X indexed write — but the gameplay impact is massive because the player instantly knows what they’re dealing with.

Tail-Chasing AI

The key behaviour that makes the higher-tier HKs genuinely threatening is the tail-chase routine. Rather than flying fixed patterns, they compare their X/Y coordinates against the player position and attempt to converge on a point behind the aircraft. Once they’re in the rear arc, they open fire. This means you can’t just park in one spot and shoot — you have to keep moving, keep turning, keep the HKs in front of you where you can hit them before they settle into your blind spot.

The AI uses a simple signed comparison to determine relative position, then selects from a set of delta-V vectors stored in a lookup table. Different aggression tiers index deeper into the table where the vectors are more aggressive. Nothing revolutionary, but it works brilliantly in practice.

Collision Rules

Collisions follow a straightforward severity model:

Glancing strikes (oblique angles) — absorbed by shields, shield energy depletes. You’ll survive but you can’t tank hits forever
Head-on collisions — fatal. You flew straight into a drone. That’s on you
Tail-on collisions — also fatal. An HK rammed you from behind while you weren’t paying attention. Also on you

The distinction is determined by checking the relative velocity vectors at the moment of sprite overlap. If both objects are moving towards each other (or one is stationary and the other closing fast on-axis), it’s treated as a head-on/tail-on and the player is destroyed. Anything else is a glancing blow that drains shields.

Drone Alley has been invaluable for tuning all of this. Isolating the combat from everything else means I can tweak the AI tables, adjust the colour thresholds and test edge cases without having to play through an entire level each time. Should have built this test harness years ago.

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