interactive n-body particle simulation in lobster

n_body_particle_simulation.lobster

import std
import vec
import color
import gl

// --- Global Particle Data (Structure of Arrays - SoA) ---
var masses:[float] = []
var positions_x:[float] = []
var positions_y:[float] = []
var velocities_x:[float] = []
var velocities_y:[float] = []

def add_new_particle(mouse_x:float, mouse_y:float):
    masses.push(rnd_float() * (0.03 - 0.003) + 0.003)
    positions_x.push(mouse_x)
    positions_y.push(mouse_y)
    velocities_x.push(0.0)
    velocities_y.push(0.0)

def main():
    let screen_width = 800.0
    let screen_height = 600.0

    fatal(gl.window("Lobster Particle Simulation", int(screen_width), int(screen_height)))
    gl.set_target_delta_time(1.0 / 60.0)

    while gl.frame() and gl.button("escape") != 1:
        let mouse_screen_pos = gl.mouse_pos(0) // Get mouse position (int2)
        let mouse_pos = float(mouse_screen_pos) // Convert to float2

        if gl.button("mouse1") >= 1:
            add_new_particle(mouse_pos.x, mouse_pos.y)

        // Update particle physics (N-body simulation style)
        for(masses.length) particle_a_idx:
            var acceleration_x = 0.0
            var acceleration_y = 0.0

            for(masses.length) particle_b_idx:
                if particle_a_idx != particle_b_idx:
                    let dist_x = positions_x[particle_b_idx] - positions_x[particle_a_idx]
                    let dist_y = positions_y[particle_b_idx] - positions_y[particle_a_idx]

                    var distance_sq = dist_x * dist_x + dist_y * dist_y
                    if distance_sq < 1.0: // Избегаем деления на ноль и слишком больших сил
                        distance_sq = 1.0

                    let distance = sqrt(distance_sq)
                    let force_magnitude = (distance - 320.0) * masses[particle_b_idx] / distance

                    acceleration_x += force_magnitude * dist_x
                    acceleration_y += force_magnitude * dist_y

            velocities_x[particle_a_idx] = velocities_x[particle_a_idx] * 0.99 + acceleration_x * masses[particle_a_idx]
            velocities_y[particle_a_idx] = velocities_y[particle_a_idx] * 0.99 + acceleration_y * masses[particle_a_idx]


        for(masses.length) particle_idx:
            positions_x[particle_idx] += velocities_x[particle_idx]
            positions_y[particle_idx] += velocities_y[particle_idx]


        gl.clear(float4 { 32.0/255.0, 32.0/255.0, 32.0/255.0, 1.0 })

        let particle_color = float4 { 64.0/255.0, 255.0/255.0, 255.0/255.0, 192.0/255.0 } // Cyan with alpha
        gl.color(particle_color)

        for(masses.length) particle_idx:
            let radius = masses[particle_idx] * 1000.0 // Radius proportional to mass
            let pos_x = positions_x[particle_idx]
            let pos_y = positions_y[particle_idx]

            gl.translate(float2 { pos_x, pos_y }):
                gl.circle(radius, 12)

main()