Add damage system - HP threshold model (Implementation A)

[wannerdev]

Description

Implements a comprehensive damage system with HP-based level demotion, sun radiation damage, and visual damage indicators.

Implementation Approach

This is Implementation A - HP + Threshold Model with i-frames and automatic level demotion.

Core Features

Health System

• Level 1: 50 HP max
• Level 2: 85 HP max
• Level 3: 120 HP max
• Satellites spawn with full HP for their level

Level Demotion Thresholds

• 100-67% HP: Level 3
• 66-34% HP: Level 2
• 33-1% HP: Level 1
• 0% HP: Destroyed

Sun Radiation Damage

• Heat radius: 1.5x sun radius
• Damage: 5 HP per second when inside heat zone
• Automatic tracking with SunExposure component
• Damage stops when satellite leaves heat zone

I-Frame System

• 0.5 second invulnerability after level demotion
• Prevents multiple demotions from single collision
• Prevents damage stacking exploits

Visual Feedback

• Red glow around damaged satellites
• Intensity increases as HP decreases
• Only shows when HP < 66%
• Alpha scales with damage (0.5 max)

Changes

• Created damage_system module
• Added Health component with level-based max HP
• Added DamageEvent for extensible damage system
• Added DemoteCooldown for i-frame tracking
• Added SunExposure for radiation damage tracking
• Implemented apply_sun_radiation_damage system
• Implemented handle_damage_events system with demotion logic
• Implemented draw_damage_effects for visual feedback
• Integrated Health and DemoteCooldown into satellite spawning
• Added DamageSystemPlugin to main app

Technical Implementation

Damage Event System

pub struct DamageEvent {
    pub target: Entity,
    pub amount: f32,
    pub source: Entity,
}

• Extensible: Any system can trigger damage
• Tracked: Source entity for damage attribution
• Flexible: Can add collision damage, weapon damage, etc.

Sun Radiation

• Tracks time in heat zone per satellite
• Applies 5 HP damage every 1 second
• Automatic component cleanup when leaving zone
• No damage outside heat radius

Level Demotion Logic

1. Check i-frame (skip if active)
2. Apply damage to HP
3. Calculate HP percentage
4. Determine new level from thresholds
5. Update sprite if level changed
6. Start i-frame cooldown
7. Despawn if HP reaches 0

Visual Damage Indicator

• Red circle around satellite
• Radius: 5.0 units
• Alpha: (1.0 - hp_pct) * 0.5
• Only renders when HP < 66%

Gameplay Impact

Strategic Depth

• Players must avoid sun's heat zone
• Close orbits are risky but rewarding
• Level 3 satellites are more durable
• Damage accumulates over time

Risk vs Reward

• Closer to sun = more energy but more damage
• Heat zone forces orbital planning
• I-frames allow recovery time
• Visual feedback helps decision making

Balancing

• 5 HP/sec sun damage
• Level 1: 10 seconds in heat zone
• Level 2: 17 seconds in heat zone
• Level 3: 24 seconds in heat zone

Benefits

• Adds challenge and strategy
• Makes positioning important
• Provides clear visual feedback
• Extensible for future damage sources
• Prevents instant death from damage stacking
• Smooth level transitions

Testing

• Launch satellite into sun's heat zone
• Verify red glow appears as HP decreases
• Check level demotion at 66% and 33% HP
• Verify satellite destroyed at 0% HP
• Test i-frame prevents rapid demotion
• Confirm sprite updates on level change
• Check damage stops outside heat zone

Future Enhancements

• Collision damage based on relative speed
• Asteroid impact damage
• Repair/healing mechanics
• HP regeneration over time
• Damage numbers floating text
• Shield system (see Implementation B)

Related Feature

Implements: Damage System (HP + Threshold Model)