render_path

app.rb

@@ -30,6 +30,7 @@ class Window < Gosu::Window
 			obj.render
 			obj.draw_vector(obj.vel, 10)
 			obj.draw_vector(obj.accel, 500, 0xff_aaffaa)
+			obj.render_path
 		end
 
 		@planets.each do |planet|
@@ -45,9 +46,15 @@ planet = Planet.new("Earth", window, 0xff_aaffaa)
 planet.pos = Vector[800, 450]
 
 cube = PhysCube.new("Cube", window, 8, 8)
-cube.vel = Vector[1, 0]
-planet.orbit([cube])
+cube.pos = Vector[800, 450 + 100]
+cube.vel = Vector[4, 0]
+
+cube2 = PhysCube.new("Cube2", window, 8, 8)
+cube2.pos = Vector[800, 450 + 150]
+cube2.vel = Vector[1, 0]
+planet.orbit([cube, cube2])
 
 window.planets << planet
 window.physobjs << cube
+window.physobjs << cube2
 window.show

physobj.rb

@@ -3,7 +3,7 @@ require "matrix"
 GRAV_CONSTANT = 1e+2
 
 class PhysObj
-	attr_accessor :world, :pos, :vel, :accel, :x, :y
+	attr_accessor :world, :saved_pos, :pos, :vel, :accel, :x, :y
 	attr_reader :name
 	def initialize(name, world)
 		@name = name
@@ -12,6 +12,7 @@ class PhysObj
 		@vel = Vector.zero(2)
 		@accel = Vector.zero(2)
 		@x, @y = 0, 0
+		@saved_pos = []
 	end
 
 	def tick
@@ -23,6 +24,13 @@ class PhysObj
 			@pos += @vel
 		end
 		@x, @y = @pos[0], @pos[1]
+		@saved_pos << @pos
+	end
+
+	def render_path
+		@saved_pos.each do |pos|
+			Gosu.draw_rect(pos[0], pos[1], 1, 1, Gosu::Color.argb(0xaa_cccccc))
+		end
 	end
 
 end
@@ -91,7 +99,7 @@ class Planet < PhysCube
 	end
 
 	private def calculate_gravity_vector(obj)
-		dir_vec = self.pos - obj.pos
+		dir_vec = self.pos - obj.pos + Vector[self.width/2, self.height/2]
 		return (GRAV_CONSTANT * self.gravity * dir_vec)/(dir_vec.magnitude ** 2)
 	end