From c1447c4de2385115e8d535b8a00432f5af63c53a Mon Sep 17 00:00:00 2001
From: Tyler Scott <tyler@dvkmo.com>
Date: Sat, 5 Feb 2022 07:54:33 +0700
Subject: [PATCH] Add collision detection and response

---
 main.lua | 84 ++++++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 82 insertions(+), 2 deletions(-)

diff --git a/main.lua b/main.lua
index 942c174..0d4bc0f 100644
--- a/main.lua
+++ b/main.lua
@@ -30,6 +30,25 @@ local function get_next_bubble_type(index, remaining_bubble_types)
   return remaining_bubble_types[love.math.random(#remaining_bubble_types)]
 end
 
+local function find_nearest_slot(x, y)
+  local nearest_slot_index = 0
+  local min_dist = math.huge
+  for i = 1, #game.bubble_slots do
+    local slot = game.bubble_slots[i]
+    if slot.bubble_type == 0 then
+      local diff_x = x - slot.x
+      local diff_y = y - slot.y
+      local dist = math.sqrt(diff_x * diff_x + diff_y * diff_y)
+      if dist < min_dist then
+        min_dist = dist
+        nearest_slot_index = i
+      end
+    end
+  end
+  assert(nearest_slot_index ~= 0, "no nearest slot found")
+  return nearest_slot_index
+end
+
 function love.load(arg)
   game.window_width, game.window_height = love.graphics.getDimensions()
 
@@ -130,8 +149,69 @@ end
 function love.update(dt)
   if game.paused then return end
   if game.next_bubble.velocity_x ~= 0 or game.next_bubble.velocity_y ~= 0 then
-    game.next_bubble.x = game.next_bubble.x + game.next_bubble.velocity_x * dt
-    game.next_bubble.y = game.next_bubble.y + game.next_bubble.velocity_y * dt
+    local next_x = game.next_bubble.x + game.next_bubble.velocity_x * dt
+    local next_y = game.next_bubble.y + game.next_bubble.velocity_y * dt
+    local collision_detection_finished = false
+
+    -- collision with ceiling
+    if next_y - game.bubble_radius <= game.level_top then
+      local nearest_slot_index = find_nearest_slot(next_x, next_y)
+      game.next_bubble.x = game.bubble_slots[nearest_slot_index].x
+      game.next_bubble.y = game.bubble_slots[nearest_slot_index].y
+      game.next_bubble.velocity_x = 0
+      game.next_bubble.velocity_y = 0
+      collision_detection_finished = true
+    end
+
+    -- collision with wall
+    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
+        local impact_x = game.level_left + game.bubble_radius
+        if next_x + game.bubble_radius >= game.level_right then
+          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 dy = game.next_bubble.velocity_y * dt * 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_y = impact_y + game.next_bubble.velocity_y * dt * ratio_after_bounce
+      end
+    end
+
+    -- collision with another bubble
+    if not collision_detection_finished then
+      for i = 1, #game.bubble_slots do
+        local slot = game.bubble_slots[i]
+        if slot.bubble_type ~= 0 then
+          local diff_x = next_x - slot.x
+          local diff_y = next_y - slot.y
+          local dist = math.sqrt(diff_x * diff_x + diff_y * diff_y)
+          if dist <= game.bubble_diameter then
+            local depth = game.bubble_diameter - dist
+            local direction_x = diff_x / dist
+            local direction_y = diff_y / dist
+            next_x = next_x + direction_x * depth
+            next_y = next_y + direction_y * depth
+            local nearest_slot_index = find_nearest_slot(next_x, next_y)
+            game.next_bubble.x = game.bubble_slots[nearest_slot_index].x
+            game.next_bubble.y = game.bubble_slots[nearest_slot_index].y
+            game.next_bubble.velocity_x = 0
+            game.next_bubble.velocity_y = 0
+            collision_detection_finished = true
+            break
+          end
+        end
+      end
+    end
+
+    if not collision_detection_finished then
+      game.next_bubble.x = next_x
+      game.next_bubble.y = next_y
+    end
   end
 
   if game.frame_by_frame then