Add move_forwards(dist) for Actor. Closes #193

pgzero/actor.py

@@ -331,6 +331,12 @@ def draw(self):
         s = self._build_transformed_surf()
         game.screen.blit(s, self.topleft)
 
+    def move_forwards(self, distance):
+        """Move this actor forwards a distance, according to its angle."""
+        angleInRads = radians(self.angle)
+        self.x += cos(angleInRads) * distance
+        self.y += sin(angleInRads) * -distance
+
     def angle_to(self, target):
         """Return the angle from this actors position to target, in degrees."""
         if isinstance(target, Actor):

test/test_actor.py

@@ -110,6 +110,31 @@ def test_rotation(self):
             a.angle += 1.0
         self.assertEqual(a.pos, (100.0, 100.0))
 
+    def test_move_forwards_ne(self):
+        """move fwd should change pos correctly when facing roughly NE"""
+        a = Actor('alien', pos=(100.0, 200.0))
+        # the angle for a 3 4 5 triangle
+        a.angle = 53.1301024
+        a.move_forwards(5)
+        self.assertAlmostEqual(a.x, 103)
+        self.assertAlmostEqual(a.y, 196)
+
+    def test_move_forwards_sw(self):
+        """Move fwd should change pos correctly when facing roughly SW"""
+        a = Actor('alien', pos=(100.0, 200.0))
+        a.angle = 180 + 53.1301024
+        a.move_forwards(5)
+        self.assertAlmostEqual(a.x, 97)
+        self.assertAlmostEqual(a.y, 204)
+
+    def test_move_forwards_zero(self):
+        """"""
+        a = Actor('alien', pos=(100.0, 200.0))
+        a.angle = 53.1301024
+        a.move_forwards(0)
+        self.assertEqual(a.x, 100.0)
+        self.assertEqual(a.y, 200.0)
+
     def test_opacity_default(self):
         """Ensure opacity is initially set to its default value."""
         a = Actor('alien')