get player dir sprite swapping working

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defold_game/main/player/player.script

@@ -0,0 +1,86 @@
+local ACCELERATION = 100
+local DECELERATION = 200
+local MAX_SPEED = 400
+local WHEEL_BASE = 80
+
+local UP = vmath.vector3(0, 1, 0)
+
+local DIRECTIONS = { "n", "ne", "e", "se", "s", "sw", "w", "nw" }
+
+local function get_direction(rot)
+    local forward = vmath.rotate(rot, UP)
+    local angle = math.deg(math.atan2(forward.x, forward.y))
+    if angle < 0 then angle = angle + 360 end
+    local index = math.floor((angle + 22.5) / 45) % 8 + 1
+    return DIRECTIONS[index]
+end
+
+function init(self)
+    msg.post(".", "acquire_input_focus")
+
+    self.left_speed = 0
+    self.right_speed = 0
+    self.current_anim = nil
+    self.left_fwd = false
+    self.left_rev = false
+    self.right_fwd = false
+    self.right_rev = false
+end
+
+local function update_speed(speed, drive, dt)
+    if drive ~= 0 then
+        local target = drive * MAX_SPEED
+        local step = ACCELERATION * dt
+        if speed < target then
+            return math.min(speed + step, target)
+        else
+            return math.max(speed - step, target)
+        end
+    else
+        local step = DECELERATION * dt
+        if speed > 0 then
+            return math.max(speed - step, 0)
+        else
+            return math.min(speed + step, 0)
+        end
+    end
+end
+
+function update(self, dt)
+    local left_drive  = (self.left_fwd  and 1 or 0) - (self.left_rev  and 1 or 0)
+    local right_drive = (self.right_fwd and 1 or 0) - (self.right_rev and 1 or 0)
+
+    self.left_speed  = update_speed(self.left_speed,  left_drive,  dt)
+    self.right_speed = update_speed(self.right_speed, right_drive, dt)
+
+    -- differential drive: speed difference creates rotation, average creates forward motion
+    local linear_speed = (self.left_speed + self.right_speed) / 2
+    local angular_vel = (self.right_speed - self.left_speed) / WHEEL_BASE
+
+    -- pprint({rot_changes = angular_vel * dt})
+    local rot = go.get_rotation()
+    rot = rot * vmath.quat_rotation_z(angular_vel * dt)
+    go.set_rotation(rot)
+
+    go.set_rotation(vmath.conj(rot), "body")
+
+    local p = go.get_position()
+    p = p + vmath.rotate(rot, UP * linear_speed * dt)
+    go.set_position(p)
+
+    -- switch animation when facing direction changes
+    local dir = get_direction(rot)
+    if dir ~= self.current_anim then
+      self.current_anim = dir
+      msg.post("body#body", "play_animation", { id = hash(dir) })
+    end
+end
+
+function on_input(self, action_id, action)
+    local held = action.pressed or not action.released
+    if     action_id == hash("a_key") then self.left_fwd  = held
+    elseif action_id == hash("q_key") then self.left_rev  = held
+    elseif action_id == hash("d_key") then self.right_fwd = held
+    elseif action_id == hash("e_key") then self.right_rev = held
+    end
+end