Game Feel & Polish for Nethercore ZX

Game feel ("juice") transforms functional mechanics into satisfying experiences. All code MUST be deterministic for rollback netcode.

Core Principles

Screen Shake

struct ScreenShake {
    intensity: f32,
    duration: u32,
    remaining: u32,
}

impl ScreenShake {
    fn trigger(&mut self, intensity: f32, duration: u32) {
        self.intensity = intensity;
        self.duration = duration;
        self.remaining = duration;
    }

    fn update(&mut self) -> (f32, f32) {
        if self.remaining == 0 { return (0.0, 0.0); }

        let t = self.remaining as f32 / self.duration as f32;
        let current = self.intensity * t;
        let offset_x = (random() * 2.0 - 1.0) * current;
        let offset_y = (random() * 2.0 - 1.0) * current;

        self.remaining -= 1;
        (offset_x, offset_y)
    }
}

Shake Intensity Guide

Hit Pause (Freeze Frames)

Momentary freeze on impact adds weight:

struct HitPause { remaining: u32 }

impl HitPause {
    fn trigger(&mut self, frames: u32) {
        self.remaining = self.remaining.max(frames);
    }

    fn is_paused(&self) -> bool { self.remaining > 0 }

    fn update(&mut self) {
        if self.remaining > 0 { self.remaining -= 1; }
    }
}

fn update(game: &mut Game) {
    game.hit_pause.update();
    if game.hit_pause.is_paused() { return; }  // Skip gameplay
    // Normal update...
}

Hit Pause Guide

Visual Feedback

Flash on Hit

fn render_entity(e: &Entity) {
    if e.flash_timer > 0 {
        material_emissive(0xFFFFFFFF);  // White flash
    }
    draw_mesh(e.mesh);
    material_emissive(0x000000FF);  // Reset
}

Scale Bounce

fn update_bounce(scale: &mut f32, target: f32, velocity: &mut f32) {
    let diff = target - *scale;
    *velocity += diff * 0.3;  // Spring force
    *velocity *= 0.8;  // Damping
    *scale += *velocity;
}

Audio Feedback

fn on_hit(damage: i32) {
    play_sound(SOUND_HIT);
    if damage > 20 {
        play_sound(SOUND_HEAVY_HIT);
    }
}

Particle Hints

For particle effects (dust, sparks, debris):

// Spawn burst on landing
if just_landed {
    for _ in 0..5 {
        spawn_particle(Particle {
            pos: player_pos,
            vel: (random() * 2.0 - 1.0, random() * 0.5),
            life: 15,
            color: 0x888888FF,
        });
    }
}

Quick Checklist

• Screen shake on impacts
• Hit pause on heavy attacks
• Visual flash on damage
• Audio for all interactions
• Particles for contacts
• Anticipation before big moves
• Follow-through after actions

References

• references/advanced-techniques.md - Complex effects, camera tricks

Related Skills

• zx-dev/rendering-techniques - Visual effects implementation
• procedural-sounds - Sound effect generation