Use idiomatic initialization, and also more reorganizing.

Makefile

@@ -1,11 +1,4 @@
-PLAYDATE_SDK_PATH := ~/playdate
-GAME := Crong
-
 all: build
 
-build: clean
-	mkdir -p build
-	cd src && PLAYDATE_SDK_PATH=$(PLAYDATE_SDK_PATH) $(PLAYDATE_SDK_PATH)/bin/pdc -k main.lua ../$(GAME).pdx
-
-clean:
-	rm -rf $(GAME).pdx
+build:
+	make -C src/

src/Makefile

@@ -0,0 +1,10 @@
+PLAYDATE_SDK_PATH := ~/playdate
+GAME := Crong
+
+all: build
+
+build: clean
+	PLAYDATE_SDK_PATH=$(PLAYDATE_SDK_PATH) $(PLAYDATE_SDK_PATH)/bin/pdc -k main.lua ../$(GAME).pdx
+
+clean:
+	rm -rf ../$(GAME).pdx

src/ball.lua

@@ -1,12 +1,12 @@
 import "pixie"
 
-class("Ball").extends(Pixie)
+class("Ball", {
+         direction = {x=-1, y=1},
+         speed     = 3,
+}).extends(Pixie)
 
 function Ball:init(width, height, color, x, y)
    Ball.super.init(self, width, height, color, x, y)
-   self.dirX = -1
-   self.dirY = 1
-   self.speed = 3
    return self
 end
 
@@ -15,23 +15,23 @@ function Ball:levelUp()
 end
 
 function Ball:move()
-   self:moveBy(self.dirX * self.speed,
-               self.dirY * self.speed)
+   self:moveBy(self.direction.x * self.speed,
+               self.direction.y * self.speed)
 end
 
 function Ball:setDirection(x, y)
-   x = x or self.dirX
-   y = y or self.dirY
-   self.dirX = x
-   self.dirY = y
+   x = x or self.direction.x
+   y = y or self.direction.y
+   self.direction.x = x
+   self.direction.y = y
 end
 
 function Ball:_normalizePosition()
    local changeVector = Ball.super._normalizePosition(self)
    if changeVector[1] ~= 0 then
-      self.dirX = changeVector[1]
+      self.direction.x = changeVector[1]
    end
    if changeVector[2] ~= 0 then
-      self.dirY = changeVector[2]
+      self.direction.y = changeVector[2]
    end
 end