basic AABB collision resolution

1 files changed, 163 insertions, 0 deletions

diff --git a/src/phys.lua b/src/phys.lua
new file mode 100644
index 0000000..a57bccd
--- /dev/null
+++ b/src/phys.lua
@@ -0,0 +1,163 @@
+phys = {}
+
+local world = {}
+phys.world = world
+
+world.boxes = {}
+world.layers = {}
+
+-- There are a few primary physics layers:
+--
+-- * Hard: for hard collisions that do not allow things in whatsoever
+-- * Soft: for collisions that push other things away over time
+-- * Player_Hurtbox: collision box that hurts the player
+-- * Player_Hitbox: collision box from the player that damages things
+-- * Enemy_Hurtbox: collision box that hurts enemies
+-- * Enemy_Hitbox: collision box from an enemy that damages things
+--
+-- You can use whatever physics layer you want, but these are the standard ones
+
+local function aabb_x(ax, aw, bx, bw)
+  return ax < bx + bw and bx < ax + aw
+end
+
+local function aabb_y(ay, ah, by, bh)
+  return ay < by + bh and by < ay + ah
+end
+
+local function aabb(ax, ay, aw, ah, bx, by, bw, bh)
+  return
+    ax < bx + bw and bx < ax + aw and
+    ay < by + bh and by < ay + ah
+end
+
+local function add_box_to_layers(box)
+  for _, layer in ipairs(box.layers) do
+    if not world.layers[layer] then
+      world.layers[layer] = {}
+    end
+    table.insert(world.layers[layer], box)
+  end
+end
+
+phys.Box = {}
+phys.Box.__index = phys.Box
+
+function phys.Box.new(
+  x, y,
+  width, height,
+  opts
+)
+  opts = opts or {}
+
+  local self = setmetatable({}, phys.Box)
+
+  self.x = x
+  self.y = y
+
+  self.offsetx = opts.offsetx or 0
+  self.offsety = opts.offsety or 0
+
+  self.width = width
+  self.height = height
+
+  self.layers = opts.layers or {"hard"}
+  self.mask = opts.mask or {}
+
+  self.touching_down = false
+  self.touching_up = false
+  self.touching_vertically = false
+  self.touching_left = false
+  self.touching_right = false
+  self.touching_horizontally = false
+
+  add_box_to_layers(self)
+
+  return self
+end
+
+function phys.Box:get_rect()
+  return
+    self.x + self.offsetx,
+    self.y + self.offsety,
+    self.width,
+    self.height
+end
+
+function phys.Box:update(velx, vely, dt)
+  local resx = self.x + velx * dt
+  local resy = self.y + vely * dt
+
+  local small_side = math.min(self.width, self.height)
+  local steps = math.ceil(vec_len(velx * dt, vely * dt) / small_side)
+
+  self.touching_down = false
+  self.touching_up = false
+  self.touching_vertically = false
+  self.touching_left = false
+  self.touching_right = false
+  self.touching_horizontally = false
+
+  -- this block is fat. much like a certain croatian...
+  for i=1, steps do
+    local p = i / steps
+
+    local boxx = resx + self.offsetx + velx * dt * p
+    local boxy = resy + self.offsety + vely * dt * p
+
+    for _, layer in ipairs(self.mask) do
+      for _, other in ipairs(world.layers[layer] or {}) do
+        if other ~= self then
+          local ox = other.x + other.offsetx
+          local oy = other.y + other.offsety
+
+          if aabb(
+            boxx, boxy, self.width, self.height,
+            ox, oy, other.width, other.height
+          ) then
+            if aabb_x(self.x + self.offsetx, self.width, ox, other.width) then
+              if vely > 0 then
+                resy = oy - self.height - self.offsety
+                self.touching_down = true
+              else
+                resy = oy + other.height - self.offsety
+                self.touching_up = true
+              end
+              self.touching_vertically = true
+            elseif aabb_y(self.y + self.offsety, self.height, oy, other.height) then
+              if velx > 0 then
+                resx = ox - self.width - self.offsetx
+                self.touching_left = true
+              else
+                resx = ox + other.width - self.offsetx
+                self.touching_right = true
+              end
+              self.touching_horizontally = true
+            end
+          end
+        end
+      end
+    end
+
+    if self.touching_horizontally then
+      velx = 0
+    end
+    if self.touching_vertically then
+      vely = 0
+    end
+
+    if self.touching_horizontally or self.touching_vertically then
+      break
+    end
+  end
+
+  self.x = resx
+  self.y = resy
+
+  return velx, vely
+end
+
+function phys.Box:draw()
+  local x, y, w, h = self:get_rect()
+  love.graphics.rectangle("line", x, y, w, h)
+end