ball.lua - implement a random visiting ball

The mobs are characters to animate.  They're sorted by screen depth,
so that nearer ones render over farther ones.

arena.lua

@@ -0,0 +1,86 @@
+
+
+
+local sideHeight = 35
+local width = 55
+local topHeight = 20
+local polys = {
+   {
+      0, 0, width/2, topHeight/2,
+      0, topHeight, -width/2,  topHeight/2,
+   },
+   {
+      0, topHeight, width/2, topHeight/2,
+      width/2, topHeight/2 + sideHeight, 0, topHeight + sideHeight,
+   },
+   {
+      0, topHeight, -width/2, topHeight/2,
+	 -width/2, topHeight/2 + sideHeight, 0, topHeight + sideHeight,
+   },
+}
+
+
+
+
+return function(size, discs, topCol, rightCol, leftCol)
+   assert(size > 0)
+   for disc in pairs(discs) do
+      assert(disc >= -size and disc <= size)
+   end
+
+   local colours = {topCol, rightCol, leftCol}   
+   local function drawCube(x, y)
+      love.graphics.push()
+      love.graphics.translate(x, y)
+      for ix, poly in ipairs(polys) do
+	 love.graphics.setColor(colours[ix])
+	 love.graphics.polygon("fill", poly)
+      end
+      love.graphics.pop()
+   end
+
+   local function getHeight()
+	 return size*(topHeight/2 + sideHeight) + topHeight/2
+   end
+
+   local x = love.graphics.getWidth()/2
+   local y = love.graphics.getHeight()/2 - getHeight()/2;
+
+   local function qpos2Coords(se, sw)
+      return x + se * width/2 - sw * width/2,
+	 y + (se + sw)*(topHeight/2+sideHeight)
+   end
+
+   return {
+      getDepth = function() return -1; end,
+      
+      getWidth = function()
+	 return size*width*2
+      end,
+   
+      getHeight = getHeight,
+
+      getSize = function() return size; end,
+      getCubeSideHeight = function() return sideHeight; end,
+      getCubeTopHeight = function() return topHeight; end,
+      getCubeHeight = function() return sideHeight+topHeight; end,
+      getCubeWidth = function() return width; end,
+      getRowHeight = function() return sideHeight+topHeight/2; end,
+      getColWidth = function() return width/2; end,
+      qpos2Coords = qpos2Coords,
+      
+      draw = function()
+	 for se = 0, size-1 do
+	    for sw = 0, size-1 do
+	       if (se + sw < size) then
+		  local x, y = qpos2Coords(se, sw)
+		  drawCube(x, y)
+	       end
+	    end
+	 end
+      end,
+      
+      update = function(dt)
+      end,
+   }
+end

ball.lua

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+local mkHopper = require "hopper"
+local dirs = {"se", "sw", "ne", "nw"}
+local height = 10;
+
+return function(arena)
+   local self
+   local function update(dt, se, sw)
+      if se+sw >= arena.getSize() then
+	 self.dead = true
+	 return
+      end
+      
+      local dir = dirs[math.random(2)]
+      self.jump(dir)
+   end
+   local function draw(x, y )
+      love.graphics.setColor(128,0,0);
+      love.graphics.circle("fill", x, y, height)
+   end
+   
+   self = mkHopper(arena, draw, update)
+   return self
+end

hopper.lua

@@ -0,0 +1,202 @@
+
+
+local jumpHeight = 10
+local jumpDist = 20
+local jumpDirs = {
+   --  { se-axis, sw-axis, path x-multiplier, path reverse }
+   ne = {0, -1, -1, true},
+   nw = {-1, 0, 1, true},
+   se = {1, 0, 1, false},
+   sw = {0, 1, -1, false},
+}
+
+--[[ 
+
+Jump equation, assuming y is up the screen and gravity down, chosen so
+that vy and ay are +ve:
+
+    y = y0 - vy*t + ay*t*t  (A)
+    x = x0 + vx*t           (B)
+
+Jump starts at t0, y0 and x0.
+Jump ends at tend, yend and xend.
+Jump peak is at ypeak.
+These are all known.
+
+We want to infer vx, ay and vy.
+
+We can get vx thus:
+
+    xend = x0 + vx*tend
+    vx = (xend - x0) / tend (C)
+
+Next to get ay and vy. For simplicity, let:
+
+     yend2 = yend - y0
+     ypeak2 = ypeak - y0
+
+
+Using (A) to get vy:
+
+    y = y0 - vy*t + ay*t*t
+    vy*t = y0 - y + ay*t*t
+    vy*t = ay*t*t - yend2
+    vy = (ay*t*t - yend2)/t
+    vy = ay*t - yend2/t  (D)
+
+Using (D) at time tend:
+
+    vy = ay*tend - yend2/tend  (E)
+
+Using (D) at time tpeak:
+
+    vy = ay*tpeak - ypeak2/tpeak  (F)
+
+Unfortunately we still don't know tpeak, but we can eliminate it.
+
+Knowing that dy/dt = 0 means:
+
+    dy/dt = -vy + 2*ay*t = 0
+
+By definition the time at this point is tpeak, so:
+
+    vy = 2*ay*tpeak
+    tpeak = 0.5*vy/ay
+
+So eliminating tpeak in (F):
+
+    vy = ay*tpeak - ypeak2/tpeak = ay*(0.5*vy/ay) - ypeak2/(0.5*vy/ay)
+    vy = 0.5*vy - ypeak2*ay/(0.5*vy)
+    vy = 0.5*vy - 2*ypeak2*ay/vy
+    2*vy = vy - 4*ypeak2*ay/vy
+    4*ypeak2*ay/vy = vy - 2*vy
+    4*ypeak2*ay/vy = -vy
+    4*ypeak2*ay = -vy^2
+    ay = -0.25*vy^2/ypeak2 (G)
+
+    vy = sqrt(-4*ypeak2*ay)
+    vy = 2*sqrt(-ypeak2*ay) (H)
+
+Eliminating vy using (H) and (E):
+
+    vy = 2*sqrt(-ypeak2*ay) = ay*tend - yend2/tend
+    -4*ypeak2*ay = (ay*tend - yend2/tend)^2
+    -4*ypeak2*ay = ay^2*tend^2 + yend2^2/tend^2 - 2*ay*tend*yend2/tend
+    0 = ay^2*tend^2 + yend2^2/tend^2 - 2*ay*yend2 + 4*ypeak2*ay
+    0 = ay^2*tend^2 + 4*ypeak2*ay - 2*ay*yend2 + yend2^2/tend^2 
+    0 = ay^2*tend^2 + ay*(4*ypeak2 - 2*yend2) + yend2^2/tend^2 
+
+This is a quadratic of the form:
+
+    0 = a*ay^2 + b*ay + c
+
+Using the quadratic solution equation:
+
+    ay = (-b +/- sqrt(b^2 - 4*a*c)/(2*a)
+
+With
+
+    a = tend^2
+    b = 4*ypeak2 - 2*yend2
+    c = yend2^2/tend^2
+
+Having calculated ay, we can get vy from 
+
+    vy = ay*tend - yend2/tend  (E)
+
+]]--
+
+local function newJumpPath(jumpDist, jumpHeight)
+   local steps = 5
+   local vx = jumpDist/steps
+   
+   local x0 = 0
+   local y0 = 0
+   local ypeak = -jumpHeight/2
+   local yend = jumpHeight
+   local ypeak2 = ypeak - y0
+   local yend2 = yend - y0
+   local tend = 5
+   local a = tend^2
+   local b = 4*ypeak2 - 2*yend2
+   local c = yend2^2/tend^2
+   local ay = 0.5*(-b + math.sqrt(b^2 - 4*a*c))/a
+   local vy = ay*tend - yend2/tend 
+   local path = {}
+   -- print(vy, ay) # DEBUG
+   for t = 0,tend do
+      table.insert(path, {x0 + vx*t,
+			  y0 - vy*t + ay*t*t})
+   end
+   --[[ DEBUG
+   for i in ipairs(path) do
+      print (i, path[i][1], path[i][2])
+   end
+   ]]--
+   
+   return path
+end
+
+local frameDuration = 0.1 -- millis
+local function time2frame(time)
+   return 1 + math.floor(time / frameDuration)
+end
+
+local function jumpDelta(frame, dir, path)
+   local _, _, mx, isReverse = unpack(jumpDirs[dir])
+   local ox, oy = unpack(path[1]) -- path offset
+   if isReverse then -- reverse the path sequence
+      frame = 1 + #path - frame
+      ox, oy = unpack(path[#path]) 
+   end
+   local dx, dy = unpack(path[frame])
+   return dx*mx-ox*mx, dy-oy
+end
+
+-- constructor
+return function(arena, draw, update)
+   assert(arena ~= nil, "arena must not be nil")
+   local jumpTime = nil
+   local jumpDir = "se"
+   local jumpFrame = 1
+   local se, sw = 0, 0
+   local jumpPath = newJumpPath(arena.getColWidth(), arena.getRowHeight())
+   return {
+      getDepth = function() return sw+se; end,
+      
+      jump = function(dir)
+	 if jumpTime ~= nil then
+	    return -- already jumping
+	 end
+	 -- print("jump",dir) -- DEBUG
+	 if jumpDirs[dir] then -- it's a valid direction
+	    jumpTime = 0
+	    jumpDir = dir
+	 end
+      end,
+      
+      draw = function()
+	 local cx, cy = arena.qpos2Coords(se, sw)
+	 local dx, dy = jumpDelta(jumpFrame, jumpDir, jumpPath)
+	 draw(cx+dx, cy+dy, se, sw)
+      end,
+   
+      update = function(dt)
+	 if jumpTime ~= nil then
+	    jumpTime = jumpTime + dt
+	    jumpFrame = time2frame(jumpTime)
+	    if jumpFrame > #jumpPath then
+	       jumpTime = nil -- finished
+	       jumpFrame = 1
+
+	       -- update qpos (se, sw)
+	       local dse, dsw = unpack(jumpDirs[jumpDir])
+	       -- print("update ", se, sw, dse, dsw) -- DEBUG
+	       se = se + dse
+	       sw = sw + dsw
+	    end
+	 end
+	 update(dt, se, sw, jumpTime, jumpFrame, jumpDir)
+      end,
+   }
+end

main.lua

@@ -0,0 +1,67 @@
+
+local mkArena = require "arena"
+local mkQbert = require "qbert"
+local mkBall = require "ball"
+
+local arena = mkArena(
+   7,
+   {3, -3},
+   {255, 0, 0}, {0, 255, 0}, {0, 0, 255}
+)
+local time = 0
+local qbert = mkQbert(
+   arena
+)
+local mobs = { qbert, arena }
+
+function love.load()
+
+end
+
+function love.draw()
+   for ix, mob in ipairs(mobs) do
+      mob.draw()
+   end
+end
+
+
+
+function love.update(dt)
+
+   time = time + dt
+   if time > 10 then
+      time = 0
+      table.insert(mobs, mkBall(arena))
+   end
+   
+   if love.keyboard.isDown('i') then
+      qbert.jump('ne')
+   end
+   if love.keyboard.isDown('u') then
+      qbert.jump('nw')
+   end
+   if love.keyboard.isDown('k') then
+      qbert.jump('se')
+   end
+   if love.keyboard.isDown('j') then
+      qbert.jump('sw')
+   end
+   if love.keyboard.isDown('escape') then
+      love.event.quit(0)
+   end
+   
+
+   for ix, mob in ipairs(mobs) do
+      mob.update(dt)
+   end
+
+   local mobs2 = {}
+   for ix, mob in ipairs(mobs) do
+      if not mob.dead then
+	 mobs2[#mobs2+1] = mob
+      end
+   end
+
+   table.sort(mobs2, function(a, b) return a.getDepth() < b.getDepth(); end)
+   mobs = mobs2
+end

qbert.lua

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+
+mkHopper = require "hopper"
+local height = 10
+local width = height
+
+local draw = function(x, y, se, sw)
+   love.graphics.setColor(128,128,0);
+   love.graphics.circle("fill", x, y, height)
+end
+
+local update = function(dt, se, sw, jumpTime, jumpFrame, jumpDir)
+end
+
+-- constructor
+return function(arena)
+   local self = mkHopper(arena, draw, update)
+   return self
+end