add demoscript

minifb.jl

@@ -0,0 +1,173 @@
+# -*- coding: utf-8 -*-
+using LinearAlgebra
+
+using Plots
+using Distributions
+using MiniFB
+using Plots
+using FileIO
+using ImageTransformations
+
+using GeometryObjects
+
+const WIDTH = 600
+const HEIGHT = 600
+
+function populate_buffer!(buffer, img)
+    global WIDTH, HEIGHT
+    buffer .= zero(UInt32)
+    h, w = size(img)
+    ratio = min(1, HEIGHT/h, WIDTH/w)
+    nimg = imresize(img, ratio=ratio)
+    nh, nw = size(nimg)
+    oh = (HEIGHT-nh) ÷ 2
+    ow = (WIDTH-nw) ÷ 2
+    for i in 1:nh
+        for j in 1:nw
+            buffer[(oh+i-1)*WIDTH + ow+j] = mfb_rgb(nimg[i,j])
+        end
+    end
+end
+
+Base.@kwdef struct CollisionSystem
+    xmin::Float64 = -4
+    xmax::Float64 = 4
+    ymin::Float64 = -4
+    ymax::Float64 = 4
+    maxT::Int = 500
+    num_particles::Int = 20
+end
+
+function setup_particle(sys::CollisionSystem)
+    particles = Particle2D[]
+    num_particles = sys.num_particles
+    while length(particles) != num_particles
+        θ = 2π * rand()
+        v_abs = 0.1
+        v = Velocity2D(v_abs * cos(θ), v_abs * sin(θ))
+        m = r = rand(Uniform(0.1, 0.3))
+        x = rand(Uniform(sys.xmin + r, sys.xmax - r))
+        y = rand(Uniform(sys.ymin + r, sys.ymax - r))
+
+        c = Particle2D(
+            Circle2D(Point2D(x, y), r),
+            v,
+            m,
+        )
+
+        c_plus_r = Particle2D(
+            Circle2D(Point2D(x, y), r + v_abs),
+            v,
+            m,
+        )
+
+        any(has_contact.(Ref(c_plus_r), particles)) && continue
+        push!(particles, c)
+    end
+    return particles
+end
+
+function move!(sys::CollisionSystem, pt::Point2D, v::Velocity2D, r::Real=0, Δt=1.)
+    pt .+= Δt .* v # do not use `pt += v`
+    if pt.y  ≥ sys.ymax - r
+        pt.y = 2(sys.ymax - r) - pt.y
+        v.y = -v.y
+    end
+    if pt.y ≤ (sys.ymin + r)
+        pt.y = 2(sys.ymin + r) - pt.y
+        v.y = -v.y
+    end
+
+    if pt.x ≥ (sys.xmax - r)
+        pt.x = 2(sys.xmax - r) - pt.x
+        v.x = -v.x
+    end
+    if pt.x ≤ (sys.xmin + r)
+        pt.x = 2(sys.xmin + r) - pt.x
+        v.x = -v.x
+    end
+    return pt, v
+end
+
+move!(sys::CollisionSystem, p::Particle2D; Δt=1.) = move!(sys, p.c.pt, p.v, p.c.r, Δt)
+
+dist(pt1, pt2) = sqrt((pt1.x - pt2.x)^2 + (pt1.y - pt2.y)^2)
+has_contact(c1::Circle2D, c2::Circle2D) = c1.r + c2.r ≥ dist(c1.pt, c2.pt)
+has_contact(p1::Particle2D, p2::Particle2D) = has_contact(p1.c, p2.c)
+
+function minifb(sys::CollisionSystem)
+    particles = setup_particle(sys)
+    Δt = 0.1
+    accumΔt = 0.0
+    cnt = 0
+
+    buf = IOBuffer()
+    buffer = zeros(UInt32, HEIGHT*WIDTH)
+    window = mfb_open_ex(
+        "Elastic Collision 2D",
+        WIDTH, HEIGHT,
+        MiniFB.WF_RESIZABLE,
+    )
+    while true
+        accumΔt += Δt
+        move!.(Ref(sys), particles; Δt)
+        # naive collision algorithm
+        for i in 1:length(particles)
+            for j in (i + 1):length(particles)
+                particle1 = particles[i]
+                particle2 = particles[j]
+                c1 = particle1.c
+                c2 = particle2.c
+                # update c1.v and c2.v
+                if has_contact(c1, c2)
+                    pt1 = c1.pt
+                    pt2 = c2.pt
+
+                    v1 = particle1.v
+                    v2 = particle2.v
+                    m1 = particle1.m
+                    m2 = particle2.m
+
+                    # correct position so that c1 and c2 does not contact
+                    while has_contact(c1, c2)
+                        c1.pt .-= 0.015 .* v1
+                        c2.pt .-= 0.015 .* v2
+                    end
+
+                    # update velocity
+                    v1_next = v1 - 2m2 / (m1 + m2) * dot(v1 - v2, pt1 - pt2) * (pt1 - pt2) / dot(pt1 - pt2, pt1 - pt2)
+                    v2_next = v2 - 2m1 / (m2 + m1) * dot(v2 - v1, pt2 - pt1) * (pt2 - pt1) / dot(pt2 - pt1, pt2 - pt1)
+                    particle1.v .= v1_next
+                    particle2.v .= v2_next
+
+                end
+            end
+        end
+
+        if accumΔt ≥ 1.
+            cnt += 1
+            s = plot(
+                size=(WIDTH, HEIGHT),
+                xlim=(sys.xmin, sys.xmax), ylim=(sys.ymin, sys.ymax),
+                aspect_ratio=:equal, legend=false,
+                grid=false, ticks=false,
+                framestyle=:box,
+            )
+            plot!(s, particles)
+            plot!(s, title="$cnt")
+            accumΔt = zero(accumΔt)
+
+            show(buf, MIME("image/png"), s)
+            img = buf |> load
+            take!(buf)
+            populate_buffer!(buffer, img)
+            state = mfb_update(window, buffer)
+            if state!= MiniFB.STATE_OK
+                break
+            end
+        end
+    end
+    mfb_close(window)
+end
+
+minifb(CollisionSystem(;xmin=-8, xmax=8, num_particles=20))