test quad primitive expand

Author: boydm

test/scenic/primitive/quad_test.exs

@@ -81,4 +81,35 @@ defmodule Scenic.Primitive.QuadTest do
     assert Quad.contains_point?(@convex, {400, 520}) == false
     assert Quad.contains_point?(@convex, {100, 520}) == false
   end
+
+
+  # ============================================================================
+  # expand
+
+  # only works if it is square...
+  defp quad_square_area({{x0,y0}, {x1,y1}, {x2,y2}, {x3,y3}}) do
+    w = abs(x1 - x0) * 1.0
+    h = abs(y2 - y0) * 1.0
+    w * h
+  end
+
+  test "expand clockwise works" do
+    quad = {{10,10}, {20,10}, {20,20}, {10,20}}
+    expanded = Quad.expand(quad, 2)
+    shrunk = Quad.expand(quad, -2)
+
+    assert quad_square_area(expanded) > quad_square_area(quad)
+    assert quad_square_area(shrunk) < quad_square_area(quad)
+  end
+
+  test "expand counter-clockwise works" do
+    quad = {{10,20}, {20,20}, {20,10}, {10,10}}
+    expanded = Quad.expand(quad, 2)
+    shrunk = Quad.expand(quad, -2)
+
+    assert quad_square_area(expanded) > quad_square_area(quad)
+    assert quad_square_area(shrunk) < quad_square_area(quad)
+  end
+
+
 end