local pos = here
local emitter = ParticleEmitter(vector_origin)

local particles = {}

local sounds =
{
    "npc/headcrab_poison/ph_step2.wav",
    "npc/headcrab_poison/ph_step3.wav",
    "npc/headcrab_poison/ph_step4.wav",
}

local WorldSound = WorldSound
local math_random = math.random

local function collide(self, pos, normal)
    WorldSound(sounds[math_random(#sounds)], pos, 60, math_random(25, 70))
end

local gravity = physenv.GetGravity() * 0.5
local vel = Vector()
local sdir = Vector()

local function Think()
    local delta = FrameTime()
    local c = HSVToColor(CurTime() * 30%360, 0.5, 1)
    sdir = sdir + ((VectorRand() - sdir) * delta)

    for i = 1, 2 do
        local particle = emitter:Add("sprites/light_glow02_add", pos)

        vel.x = math.Rand(-1, 1) * 25
        vel.y = math.Rand(-1, 1) * 25
        vel.z = math.Rand(2.5, 5) * 50

        vel.x = vel.x + sdir.x * 100
        vel.y = vel.y + sdir.y * 100
        vel.z = vel.z + sdir.z * 100

        -- movement
        particle:SetVelocity(vel)
        particle:SetAirResistance(0)
        particle:SetGravity(gravity)

        particle:SetCollide(true)
        particle:SetBounce(0.25)

        -- appearance
        particle:SetColor(c.r, c.g, c.b)
        particle.clr = c

        particle:SetStartAlpha(255)
        particle:SetEndAlpha(0)

        particle:SetStartSize(10)
        particle:SetEndSize(0)

        particle:SetDieTime(math.Rand(1.5, 2.5))

        particle:SetStartLength(0)
        particle:SetEndLength(0)
        particle:SetCollideCallback(collide)

        table.insert(particles, particle)
    end
end

local mat = Material("particle/Particle_Glow_04_Additive")

local render_DrawBeam = render.DrawBeam
local render_SetMaterial = render.SetMaterial

hook.Add("PostDrawTranslucentRenderables", 1, function()
    for key, particle in pairs(particles) do
        local delta = particle:GetDieTime() - particle:GetLifeTime()

        if delta > 0 then
            local pos = particle:GetPos()
            local vel = particle:GetVelocity()

            render_SetMaterial(mat)
            render_DrawBeam(pos + vel * 0.05, pos - vel * 0.25, 1 * delta, 0, 1, particle.clr)
        else
            particles[key] = nil
        end
    end
end)

hook.Add("Think", "particle_test", Think)