Gun Heat Waves & Bullet Shadows

Origins

Gun Heat Waves and Bullet Shadows were developed by the RoboWiki community to improve wave-based movement systems. These techniques help bots distinguish between actual enemy bullets and false alarms caused by energy drops from other sources.

Gun Heat Waves and Bullet Shadows are complementary techniques used in advanced movement systems, particularly Wave Surfing. They solve two related problems:

1. When can the enemy fire again? (Gun Heat Waves)
2. Where are bullets definitely not located? (Bullet Shadows)

Together, they improve wave detection accuracy and enable more precise bullet dodging.

Gun Heat Waves

The Problem

You detect enemy fire by monitoring energy drops. But sometimes the enemy's energy drops due to:

• Ramming damage
• Bullet hits from other bots (melee)
• Death
• Wall collisions (in some game modes)

This creates false wave detections. Your movement system dodges bullets that don't exist, wasting positioning and potentially moving into real danger.

The Solution

Track the enemy's gun heat. A bot can only fire when gun heat reaches zero. By modeling when the enemy's gun cools down, you can confirm whether an energy drop corresponds to an actual shot.

Detecting Energy Drops

The first step is observing the enemy's energy level each turn and detecting changes:

previousEnergy = 100.0  // Track enemy energy

on enemy scan:
  energyDrop = previousEnergy - currentEnergy
  
  if energyDrop > 0:
    classifyEnergyDrop(energyDrop)
  
  previousEnergy = currentEnergy

Classifying Energy Drops

Not every energy drop is a bullet! Here's how to tell them apart:

Color coding: ■ 🔫 Green = Real bullet (valid), ■ 💥 Red = Ram damage (ignore), ■ 🎯 Orange = Hit by bullet (ignore)

Turn	Energy Drop	Cause	How to identify
30	1.0	🔫 Fired bullet	Drop in [0.1, 3.0] + gun heat check
42	1.0	🔫 Fired bullet	Drop in [0.1, 3.0] + gun heat check
46	0.6	💥 Ram damage	Drop = 0.6 exactly
50	2.8	🎯 Hit by bullet	Drop > 3.0
54	1.0	🔫 Fired bullet	Drop in [0.1, 3.0] + gun heat check

Your bot tracks Gun heat

You cannot read the enemy's gun heat directly—you must model it based on when they fire. See Validating with Gun Heat below for the implementation.

Energy Drop Signatures

Use these patterns to classify energy drops:

Cause	Energy Drop Range	Notes
🔫 Fired bullet	0.1 – 3.0	Must also check gun heat = 0
💥 Ram damage	exactly 0.6	Fixed value; easy to filter
🎯 Hit by bullet	0.4 – 16.0	Damage = 4p + 2(p-1) if p>1
🧱 Wall collision	0 – ~3.5	= max(0, abs(velocity) × 0.5 - 1)
☠️ Inactivity penalty	0.1/turn	Rare; only if bot is idle

Validating with Gun Heat

The energy drop range [0.1, 3.0] overlaps with other damage sources. To confirm a real bullet, track the enemy's gun heat. A bot can only fire when gun heat = 0.

enemyGunHeat = 3.0  // Bots start with gun heat = 3.0

on enemy scan:
  // Gun heat cools every turn
  coolingRate = 0.1  // Default cooling rate
  enemyGunHeat = max(0, enemyGunHeat - coolingRate)
  
  // Detect and classify energy drop
  energyDrop = previousEnergy - currentEnergy
  
  if energyDrop == 0.6:
    // Ram damage - ignore
    logFalseDetection("ram")
  else if energyDrop > 3.0:
    // Hit by bullet - ignore  
    logFalseDetection("bullet hit")
  else if 0.1 <= energyDrop <= 3.0:
    // Possible bullet - validate with gun heat
    if enemyGunHeat <= 0.001:
      bulletPower = energyDrop
      heatGenerated = 1 + bulletPower / 5
      createWave(bulletPower)
      enemyGunHeat = heatGenerated
    else:
      logFalseDetection("gun not ready")

This eliminates most false waves, particularly in melee where multiple bots are shooting and ramming.

Visualizing Gun Heat

The gun heat pattern is a sawtooth wave: linear cooling interrupted by instant spikes when firing.

Phase	Turns	What happens
❄️ Initial cooldown	0 → 30	Heat cools from 3.0 to 0.0 (30 turns × 0.1)
🔫 First shot	30	Heat = 0 ✅ → Fire power 1.0 → Heat instantly becomes 1.2
❄️ Cooldown	30 → 42	Heat cools from 1.2 to 0.0 (12 turns × 0.1)
🔫 Second shot	42	Heat = 0 ✅ → Fire power 1.0 → Heat instantly becomes 1.2
❄️ Cooldown	42 → 54	Heat cools from 1.2 to 0.0
🔫 Third shot	54	Heat = 0 ✅ → Fire again

Reading "30+"

The notation "30+" means "immediately after the action on turn 30". The gun heat is 0 at the start of turn 30, then instantly jumps to 1.2 when the bot fires.

Decision Flowchart

Complete Example Timeline

Here's a full battle sequence showing how the detection → classification → validation flow works:

Turn	Enemy Energy	Drop	Classification	Gun Heat	Action
0	100.0	—	—	3.0	Round start
30	99.0	1.0	In [0.1, 3.0] → check heat	0.0 ✅	✅ Create wave (power 1.0)
31	99.0	0	No drop	1.2	—
42	98.0	1.0	In [0.1, 3.0] → check heat	0.0 ✅	✅ Create wave (power 1.0)
46	97.4	0.6	= 0.6 → ram damage	0.8	❌ Ignore
50	94.6	2.8	> 3.0 → hit by bullet	0.4	❌ Ignore
54	93.6	1.0	In [0.1, 3.0] → check heat	0.0 ✅	✅ Create wave (power 1.0)

Bullet Shadows

The Problem

When you dodge a bullet, you move perpendicular to the enemy. But what if you move toward the enemy? Could you walk into a bullet you're trying to dodge?

Bullet Shadows answer: "Where can bullets not be?"

The Core Insight

Once you detect a bullet's position (either by being hit or by seeing it pass), you know:

1. The bullet's current location
2. The bullet's trajectory (straight line from enemy to initial bearing)
3. All points behind the bullet (closer to the enemy) are safe zones—no bullet can exist there

This creates a "shadow" region where you're guaranteed not to encounter that specific bullet.

Implementation

bulletShadows = []

on bullet detected:
  shadow = {
    origin: enemyFirePosition,
    bulletPosition: currentBulletPosition,
    trajectory: angle(origin -> bulletPosition),
    speed: bulletSpeed
  }
  bulletShadows.append(shadow)

function isInShadow(position):
  for shadow in bulletShadows:
    vectorToPosition = position - shadow.origin
    vectorToBullet = shadow.bulletPosition - shadow.origin
    
    if length(vectorToPosition) < length(vectorToBullet):
      if angle(vectorToPosition) ≈ shadow.trajectory:
        return true  // Position is behind the bullet
  return false

Use Cases

1. Aggressive Movement

Move toward the enemy immediately after their bullet passes:

if mostDangerousWave.hasPassedMe() or isInShadow(myPosition):
  moveTowardEnemy()
else:
  continueEvading()

2. Wave Surfing Refinement

Exclude shadow regions from danger calculations:

for guessFactor in reachableGFs:
  position = positionAtGF(guessFactor)
  if isInShadow(position):
    danger[guessFactor] = 0  // Perfectly safe
  else:
    danger[guessFactor] = calculateDanger(position)

3. Melee Survival

In melee, bullets come from all directions. Bullet Shadows help identify temporary safe zones:

destinations = generatePossibleMoves()
safeDestinations = [d for d in destinations if isInShadow(d)]
if safeDestinations:
  moveTo(bestOf(safeDestinations))

Combining Gun Heat Waves and Bullet Shadows

Advanced bots use both techniques together:

Wave Detection

on enemy energy drop:
  if gunHeatAllowsFire():
    wave = createWave()
    trackedWaves.append(wave)

Wave Validation

on tick:
  for wave in trackedWaves:
    if wave.shouldHaveHitMe():
      if wasHitByBullet():
        confirmWave(wave)  // Real bullet
      else:
        createBulletShadow(wave)  // Bullet missed; shadow region is safe
      trackedWaves.remove(wave)

Movement Decision

safestGF = findSafestGuessFactor(dangerProfile, bulletShadows)
destination = positionAtGF(safestGF)
if isInShadow(destination):
  useAggressiveMovement(destination)
else:
  useDefensiveMovement(destination)

Practical Tips

Gun heat tracking:

• Initialize gun heat to 3.0 when you first scan an enemy (both platforms start bots with 3.0 gun heat).
• With default cooling rate (0.1/turn), bots can first fire on turn 30.
• In melee, track gun heat separately for each enemy.

Bullet shadows:

• Clear shadows after bullets exit the battlefield or after a timeout (50-100 turns).
• Use shadows primarily for confirming wave misses, not for proactive movement (too narrow to rely on).
• Shadows work best in one-on-one; in melee, overlapping bullets complicate shadow geometry.

Performance:

• Gun heat tracking adds minimal overhead (one floating-point variable per enemy).
• Bullet shadow calculations can be expensive—limit to 5-10 active shadows maximum.

Common Mistakes

• Forgetting gun heat decay: Not subtracting cooling rate every turn leads to false positives.
• Rounding errors: Gun heat checks should use <= 0.001, not == 0, to handle floating-point precision.
• Shadow geometry bugs: Off-by-one errors in angle calculations create false safe zones.
• Over-reliance on shadows: Shadows confirm past bullets, but don't predict future danger.

When These Techniques Matter Most

Gun Heat Waves:

• Essential in melee (many false energy drops)
• Useful in one-on-one against ramming bots
• Critical for Wave Surfing accuracy

Bullet Shadows:

• Most impactful in aggressive/close-range strategies
• Helpful for post-dodge positioning
• Less useful against slow-firing or pattern-matching enemies

Next Steps

• Wave Surfing Introduction — Use Gun Heat Waves to improve wave detection
• Dodging Bullets — Reactive bullet avoidance using Bullet Shadows
• Melee Movement Tactics — Apply these techniques to multi-opponent battles -->

Further Reading

• Bullet Shadow — RoboWiki (classic Robocode)
• Wave Surfing — RoboWiki (classic Robocode)
• Waves — RoboWiki (classic Robocode)