comet particles lobster

comet.lobster

import std
import vec
import color
import gl

let WIDTH = 800
let HEIGHT = 600
let MAX_TAIL_LENGTH = 50

// Particle class to represent parts of the comet's tail
class Particle:
    x:float
    y:float
    alpha:float
    offset_y:float // For wavy motion
    speed:float    // Speed of wavy motion
    amplitude:float// Amplitude of wavy motion

def main():
    fatal(gl.window("Comet with Dynamic Tail", WIDTH, HEIGHT))
    gl.set_target_delta_time(1.0 / 60.0)

    // Comet properties
    var comet_x = 0.0
    let comet_y = HEIGHT / 2.0
    let comet_speed = 5.0

    // Tail: a vector of Particle objects
    let tail:[Particle] = []

    // Main game loop
    while gl.frame() and gl.button("escape") != 1:

        // Move comet
        comet_x += comet_speed
        if comet_x > WIDTH:
            comet_x = 0.0

        // Add new particle to the head of the tail
        let new_particle = Particle {
            x: comet_x,
            y: comet_y,
            alpha: 1.0,
            offset_y: 0.0,
            speed: rnd_float() * (0.5 - 0.1) + 0.1,
            amplitude: rnd_float() * (5.0 - 1.0) + 1.0
        }
        insert(tail, 0, new_particle)

        // Limit tail length
        if tail.length > MAX_TAIL_LENGTH:
            tail.truncate(MAX_TAIL_LENGTH)


        // Update tail particles
        let current_time = gl.time()

        for(tail) p, i: // Iterate with particle (p) and index (i)
            // Fade out particle
            p.alpha -= 0.02
            p.alpha = max(0.0, p.alpha) // Clamp alpha to be >= 0

            // Add wavy motion
            let wave_angle_deg = current_time * p.speed * 50.0 + float(i) * 10.0
            p.offset_y = sin(wave_angle_deg) * p.amplitude

            // Update particle's y position with wavy motion and slight random jitter
            p.y = comet_y + p.offset_y + (rnd_float() * 2.0 - 1.0) // random.uniform(-1, 1)


        // --- Draw ---
        gl.clear(color_black)

        // Draw tail
        for(tail) p, i:
            if p.alpha > 0.0: // Only draw visible particles
                let particle_color = float4 { 1.0, 1.0, 1.0, p.alpha } // White with alpha
                gl.color(particle_color)

                // Particle size decreases with distance from comet head
                let particle_radius = max(1.0, 5.0 - float(i) * 0.1)

                gl.translate(float2 { p.x, p.y }):
                    gl.circle(particle_radius, 12) // 12 segments for small circles

        // Draw comet head
        gl.color(color_white)
        gl.translate(float2 { comet_x, comet_y }):
            gl.circle(10.0, 30) // 30 segments for a smoother comet head


main()