Change game loop to use fixed time step

main.lua

@@ -57,7 +57,7 @@ function love.load(arg)
 
   game.bubble_diameter = 60
   game.bubble_radius = game.bubble_diameter / 2
-  game.bubble_speed = 900 -- px/s
+  game.bubble_speed = 8 -- px/frame
 
   -- vertical distance between bubble center points
   game.row_gap = math.ceil(math.sqrt(
@@ -150,10 +150,13 @@ function love.load(arg)
 end
 
 function love.update(dt)
-  if game.paused then return end
+  if game.paused then
+    return
+  end
+
   if game.next_bubble.velocity_x ~= 0 or game.next_bubble.velocity_y ~= 0 then
-    local next_x = game.next_bubble.x + game.next_bubble.velocity_x * dt
+    local next_x = game.next_bubble.x + game.next_bubble.velocity_x
-    local next_y = game.next_bubble.y + game.next_bubble.velocity_y * dt
+    local next_y = game.next_bubble.y + game.next_bubble.velocity_y
     local collision_detection_finished = false
 
     -- collision with ceiling
@@ -166,7 +169,7 @@ function love.update(dt)
       collision_detection_finished = true
     end
 
-    -- collision with wall
+    -- collision with walls
     if not collision_detection_finished then
       if next_x + game.bubble_radius >= game.level_right or
          next_x - game.bubble_radius <= game.level_left then
@@ -175,13 +178,13 @@ function love.update(dt)
           impact_x = game.level_right - game.bubble_radius
         end
         local dx = impact_x - game.next_bubble.x
-        local ratio = dx / game.next_bubble.velocity_x * dt
+        local ratio = dx / game.next_bubble.velocity_x
-        local dy = game.next_bubble.velocity_y * dt * ratio
+        local dy = game.next_bubble.velocity_y * ratio
         local impact_y = game.next_bubble.y + dy
         local ratio_after_bounce = 1.0 - ratio
         game.next_bubble.velocity_x = -game.next_bubble.velocity_x
-        next_x = impact_x + game.next_bubble.velocity_x * dt * ratio_after_bounce
+        next_x = impact_x + game.next_bubble.velocity_x * ratio_after_bounce
-        next_y = impact_y + game.next_bubble.velocity_y * dt * ratio_after_bounce
+        next_y = impact_y + game.next_bubble.velocity_y * ratio_after_bounce
       end
     end
 
@@ -195,6 +198,7 @@ function love.update(dt)
           local dist = math.sqrt(diff_x * diff_x + diff_y * diff_y)
           if dist <= game.bubble_diameter then
             local depth = game.bubble_diameter - dist
+            print('depth', depth)
             local direction_x = diff_x / dist
             local direction_y = diff_y / dist
             next_x = next_x + direction_x * depth
@@ -223,17 +227,21 @@ function love.update(dt)
   end
 end
 
-function love.draw()
+function love.draw(alpha)
+  if game.paused then
+    alpha = 0
+  end
+
   -- draw background
   love.graphics.setColor(1, 1, 1, 1)
   love.graphics.draw(game.background_image, 0, 0)
   love.graphics.draw(game.background_image, game.background_width, 0)
 
   -- draw stationary bubbles
+  love.graphics.setColor(1, 1, 1, 1)
   for i = 1, #game.bubble_slots do
     local slot = game.bubble_slots[i]
     if slot.bubble_type >= 1 and slot.bubble_type <= #game.bubble_images then
-      love.graphics.setColor(1, 1, 1, 1)
       love.graphics.draw(
         game.bubble_images[slot.bubble_type],
         slot.x,
@@ -243,7 +251,6 @@ function love.draw()
         game.bubble_radius
       )
     else
-      love.graphics.setColor(0.4, 0, 0, 1)
       love.graphics.circle(
         'line',
         slot.x,
@@ -253,7 +260,7 @@ function love.draw()
     end
   end
 
-  -- draw level border
+  -- draw walls
   love.graphics.setColor(0, 0, 0, 1)
   love.graphics.rectangle(
     'line',
@@ -277,11 +284,12 @@ function love.draw()
   )
 
   -- draw next bubble
+  -- if moving, extrapolate position based on alpha value from love.run
   love.graphics.setColor(1, 1, 1, 1)
   love.graphics.draw(
     game.bubble_images[game.next_bubble.bubble_type],
-    game.next_bubble.x,
+    game.next_bubble.x + game.next_bubble.velocity_x * alpha,
-    game.next_bubble.y,
+    game.next_bubble.y + game.next_bubble.velocity_y * alpha,
     0,
     1,
     1,
@@ -314,6 +322,9 @@ function love.keypressed(key, scan_code, is_repeat)
     game.next_bubble.y = game.launcher_y
     game.next_bubble.velocity_x = 0
     game.next_bubble.velocity_y = 0
+    game.next_bubble.bubble_type = get_next_bubble_type(
+      game.next_bubble_index, {1,2,3,4,5,6,7,8}
+    )
     game.paused = false
   elseif key == 'space' then
     game.paused = not game.paused
@@ -322,3 +333,55 @@ function love.keypressed(key, scan_code, is_repeat)
     game.paused = false
   end
 end
+
+function love.run()
+  if love.load then love.load(love.arg.parseGameArguments(arg), arg) end
+
+  if love.timer then love.timer.step() end
+
+  local dt = 1/120 -- update 120 times per second
+  local accumulator = 0.0
+
+  return function()
+    if love.event then
+      love.event.pump()
+      for name, a,b,c,d,e,f in love.event.poll() do
+        if name == "quit" then
+          if not love.quit or not love.quit() then
+            return a or 0
+          end
+        end
+        love.handlers[name](a,b,c,d,e,f)
+      end
+    end
+
+    local frame_time = dt -- default in case love.timer is disabled
+
+    if love.timer then
+      frame_time = love.timer.step()
+      if frame_time > 0.25 then
+        frame_time = 0.25
+      end
+    end
+
+    accumulator = accumulator + frame_time
+
+    while (accumulator >= dt) do
+      if love.update then love.update(dt) end
+      accumulator = accumulator - dt
+    end
+
+    local alpha = accumulator / dt
+
+    if love.graphics and love.graphics.isActive() then
+      love.graphics.origin()
+      love.graphics.clear(love.graphics.getBackgroundColor())
+
+      if love.draw then love.draw(alpha) end
+
+      love.graphics.present()
+    end
+
+    if love.timer then love.timer.sleep(0.001) end
+  end
+end