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chipmunk に万有引力を設定する 5, 5 体で試してみる

-- n 体に拡張する。前回の表を pSpace のメソッド(★★ の部分)として実装した。

require "physics"; require "color"

-----------------------
-- general functions --
-----------------------
function pV(x, y)  return physics.Vect(x, y) end
function sum(list) local result = ZERO for _, v in ipairs(list) do result = result + v end return result end
---------------------------------------------------
---------------------------------------------------

function on.resize()
   W, H = platform.window:width(), platform.window:height()
   X0, Y0, UNIT = math.floor(W/2), math.floor(H/2), math.floor(H/15)
end

TICKING = false
spaceDamping = 0.9
ZERO = pV(0, 0)
LARGE = physics.misc.INFINITY()
DT = 1/(2^6)
GRAVITY = 0 -- 重力加速度の符号は鉛直方向下向きをマイナスにする。
COLOR = { -- 参考: http://www.colordic.org
--[[パステルカラー]]0xFF7F7F, 0xFF7FBF, 0xFF7FFF, 0xBF7FFF, 0x7F7FFF, 0x7FBFFF, 0x7FFFFF, 0x7FFFBF, 0x7FFF7F, 0xBFFF7F, 0xFFFF7F, 0xFFBF7F, 
--[[ビビッドカラー--]]0xFF6060, 0xFF60AF, 0xFF60FF, 0xAF60FF, 0x6060FF, 0x60AFFF, 0x60FFFF, 0x60FFAF, 0x60FF60, 0xAFFF60, 0xFFFF60, 0xFFAF60,
--[[モノトーン--]]0x5E5E5E, 0x7E7E7E, 0x9E9E9E, 0xBEBEBE, 0xDEDEDE, 0xFEFEFE, 
--[[メトロカラー--]]0x0078BA, 0x0079C2, 0x009944, 0x00A0DE, 0x00A7DB, 0x00ADA9, 0x019A66, 0x522886, 0x6CBB5A, 0x814721, 0x9B7CB6, 0x9CAEB7, 0xA9CC51, 0xB6007A, 0xBB641D, 0xD7C447, 0xE44D93, 0xE5171F, 0xE60012, 0xE85298, 0xEE7B1A, 0xF39700, 
}

-----------------
-- pBall class --
-----------------
pBall = class()
function pBall:init(mass, radius, elasticity, friction, color, group)
   self.color = color or color.black
   local inertia = physics.misc.momentForCircle(mass, 0, radius, ZERO)
   self.body = physics.Body(mass, inertia)
   self.shape = physics.CircleShape(self.body, radius, ZERO)
      :setRestitution(elasticity or 0.8)
      :setFriction(friction or 0.8)
   if group then
      self.shape:setGroup(group)
   end
end
function pBall:paint(gc)
   local pos = self.body:pos()
   local cx, cy = X0 + UNIT * pos:x(), Y0 - UNIT * pos:y()
   local radius = UNIT * self.shape:radius()
   local diameter = radius + radius
   local angle = self.body:angle()
   local x0, y0 = cx - radius, cy - radius  
   gc:setColorRGB(self.color)
   gc:fillArc(x0, y0, diameter, diameter, 0, 360)
   gc:setColorRGB(color.black)
   gc:setPen("thin")
   gc:drawArc(x0, y0, diameter, diameter, 0, 360)
   gc:drawLine(cx, cy, cx + radius * math.cos(angle), cy - radius * math.sin(angle))
end

----------------
-- pBox class --
----------------
pBox = class()
function pBox:init(mass, width, height, elasticity, friction, color, group)
   self.color = color or color.black
   local inertia = physics.misc.momentForBox(mass, width, height)
   self.body = physics.Body(mass, inertia)
   local verts = {pV(-width/2, -height/2), pV(-width/2, height/2), pV(width/2, height/2), pV(width/2, -height/2)} -- {左上, 左下, 右下, 右上}
   self.shape = physics.PolyShape(self.body, verts, ZERO)
      :setRestitution(elasticity or 0.8)
      :setFriction(friction or 0.8)
   if group then
      self.shape:setGroup(group)
   end
end
function pBox:paint(gc)
   local numVerts = self.shape:numVerts()
   local verts = {}
   for i = 1, numVerts + 1 do
      local j = i; if i > numVerts then j = 1 end
      local points = self.shape:points()[j]
      table.insert(verts, X0 + UNIT * points:x())
      table.insert(verts, Y0 - UNIT * points:y())
   end
   gc:setColorRGB(self.color)
   gc:fillPolygon(verts)
   gc:setPen("thin")
   gc:setColorRGB(color.black)
   gc:drawPolyLine(verts)
end

----------------------
-- pStaticSeg class --
----------------------
pStaticSeg = class()
function pStaticSeg:init(x1, y1, x2, y2, elasticity, friction, color, group)
   self.color = color or color.black
   local avec, bvec = pV(x1, y1),  pV(x2, y2)
   self.shape = physics.SegmentShape(nil, avec, bvec, 0.05)
      :setRestitution(elasticity or 0.8)
      :setFriction(friction or 0.8)
   if group then
      self.shape:setGroup(group)
   end
end
function pStaticSeg:paint(gc)
   local pos1 = self.shape:a()
   local x1, y1 = X0 + UNIT * pos1:x(), Y0 - UNIT * pos1:y()
   local pos2 = self.shape:b()
   local x2, y2 = X0 + UNIT * pos2:x(), Y0 - UNIT * pos2:y()
   gc:setColorRGB(self.color)
   gc:setPen("thin")
   gc:drawLine(x1, y1, x2, y2)
end

------------------
-- pSpace class --
------------------
pSpace = class()
function pSpace:init(GRAVITY)
   self.space = physics.Space()
      :setGravity(pV(0, GRAVITY))
      :setDamping(spaceDamping)
   self.objects = {}
end
function pSpace:step(DT)
   self.space:step(DT)
end
function pSpace:addObj(obj, velx, vely, cx, cy)
   obj.body:setVel(pV(velx or 0, vely or 0))
      :setPos(pV(cx or W/2, cy or H/2))
   self.space:addBody(obj.body)
      :addShape(obj.shape)
   table.insert(self.objects, obj)
end
function pSpace:addStatic(obj, cx, cy)
   if obj.body then obj.body:setPos(pV(cx or W/2, cy or H/2)) end
   self.space:addStaticShape(obj.shape)
   table.insert(self.objects, obj)
end
function pSpace:attractBetween() -- ★★ 今回実装したメソッド
   local forceTable = {}
   for r = 1, #self.objects do
      forceTable[r] = {}
      for c = 1, #self.objects do
         if r == c then
            forceTable[r][c] = ZERO
         elseif r > c then
            forceTable[r][c] = -forceTable[c][r]
         else
            local posA = self.objects[r].body:pos()
            local posB = self.objects[c].body:pos()
            local massA = self.objects[r].body:mass()
            local massB = self.objects[c].body:mass()
            local vectAB = posB - posA
            local lengthABsq = vectAB:lengthsq()
            local normAB = vectAB:normalize()
            forceTable[r][c] = normAB:mult(massA * massB/lengthABsq)
         end
      end
      self.objects[r].body:setForce(sum(forceTable[r]))
   end
end
function pSpace:paint(gc)
   gc:setColorRGB(color.gray)
   --gc:drawString(string.format("acceleration of gravity: %g", GRAVITY), 5, -3, "top")
   gc:drawString(string.format("t = %5.1f", timeElapsed), W - 100, 3, "top")
   for _, v in ipairs(self.objects) do
      v:paint(gc)
   end
end

----------------
-- Grid class --
----------------
Grid = class()
function Grid:init()
end
function Grid:paint(gc)
   gc:setPen("thin")
   gc:setColorRGB(0x6495ED)
   gc:drawLine(0, Y0, W, Y0)
   gc:drawLine(X0, 0, X0, H)
   gc:fillPolygon({W, Y0, W - 7, Y0 - 4, W - 3, Y0, W - 7, Y0 + 4, W, Y0})
   gc:fillPolygon({X0, 0, X0 - 4, 7, X0, 3, X0 + 4, 7, X0, 0})
   gc:drawString("x", W - 10, Y0 - 21)
   gc:drawString("y", X0 + 5, -6)
   gc:setColorRGB(0xCAE1FF)
   local i1 = 1; while Y0 - UNIT * i1 > 0 do gc:drawLine(0, Y0 - UNIT * i1, W, Y0 - UNIT * i1); i1 = i1 + 1 end
   local i2 = 1; while Y0 + UNIT * i2 < H do gc:drawLine(0, Y0 + UNIT * i2, W, Y0 + UNIT * i2); i2 = i2 + 1 end   
   local i3 = 1; while X0 + UNIT * i3 < W do gc:drawLine(X0 + UNIT * i3, 0, X0 + UNIT * i3, H); i3 = i3 + 1 end   
   local i4 = 1; while X0 - UNIT * i4 > 0 do gc:drawLine(X0 - UNIT * i4, 0, X0 - UNIT * i4, H); i4 = i4 + 1 end   
end

------------------
-- 確認してみる --
------------------
function reset()
   timeElapsed = 0
   grid = Grid()
   space = pSpace(GRAVITY)

   ball2 = pBall(3, 0.1, 1, 0.1, COLOR[math.random(#COLOR)]) -- (質量, 半径, 反撥係数, 摩擦力, 色 [,グループ])
   ball3 = pBall(3, 0.1, 1, 0.1, COLOR[math.random(#COLOR)]) -- (質量, 半径, 反撥係数, 摩擦力, 色 [,グループ])
   ball4 = pBall(4, 0.2, 1, 0.1, COLOR[math.random(#COLOR)]) -- (質量, 半径, 反撥係数, 摩擦力, 色 [,グループ])
   ball5 = pBall(5, 0.3, 1, 0.1, COLOR[math.random(#COLOR)]) -- (質量, 半径, 反撥係数, 摩擦力, 色 [,グループ])
   ball6 = pBall(6, 0.5, 1, 0.1, COLOR[math.random(#COLOR)]) -- (質量, 半径, 反撥係数, 摩擦力, 色 [,グループ])
         
   space:addObj(ball2, 0, 0, -3, 3) -- (オブジェクト, 初速ベクトル x, y, 初期座標 x, y)
   space:addObj(ball3, 0, 0, 1, 3) -- (オブジェクト, 初速ベクトル x, y, 初期座標 x, y)
   space:addObj(ball4, 0, 0, -2, -1) -- (オブジェクト, 初速ベクトル x, y, 初期座標 x, y)
   space:addObj(ball5, 0, 0, 1, -1) -- (オブジェクト, 初速ベクトル x, y, 初期座標 x, y)
   space:addObj(ball6, 0, 0, 0, 0) -- (オブジェクト, 初速ベクトル x, y, 初期座標 x, y)
end
----------------------------------------------------------
----------------------------------------------------------
----------------------------------------------------------

function on.construction()
   reset()
end
function on.escapeKey()
   reset()
end
function on.paint(gc)
   grid:paint(gc)
   space:paint(gc)
end
function on.timer()
   space:step(DT)
   space:attractBetween()
   timeElapsed = timeElapsed + DT
   platform.window:invalidate()
end
function on.enterKey()
   if     TICKING == false then timer.start(DT); TICKING = true
   elseif TICKING == true  then timer.stop();    TICKING = false
   end
end
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