tests: add bullet heightfield test

Closes #619

tests/bullet/test_bullet_heightfield.py

@@ -0,0 +1,45 @@
+import pytest
+# Skip these tests if we can't import bullet.
+bullet = pytest.importorskip("panda3d.bullet")
+
+from panda3d.bullet import BulletWorld, BulletRigidBodyNode, ZUp
+from panda3d.bullet import BulletHeightfieldShape, BulletSphereShape
+from panda3d.core import NodePath, PNMImage
+
+
+def make_node(name, BulletShape, *args):
+    # Returns a BulletRigidBodyNode for the given shape
+    shape = BulletShape(*args)
+    node = BulletRigidBodyNode(name)
+    node.add_shape(shape)
+    return node
+
+
+def test_sphere_into_heightfield():
+    root = NodePath("root")
+    world = BulletWorld()
+    # Create PNMImage to construct Heightfield with
+    img = PNMImage(10, 10, 1)
+    img.fill_val(255)
+    # Make our nodes
+    heightfield = make_node("Heightfield", BulletHeightfieldShape, img, 1, ZUp)
+    sphere = make_node("Sphere", BulletSphereShape, 1)
+    # Attach to world
+    np1 = root.attach_new_node(sphere)
+    np1.set_pos(0, 0, 1)
+    world.attach(sphere)
+
+    np2 = root.attach_new_node(heightfield)
+    np2.set_pos(0, 0, 0)
+    world.attach(heightfield)
+
+    assert world.get_num_rigid_bodies() == 2
+    test = world.contact_test_pair(sphere, heightfield)
+    assert test.get_num_contacts() > 0
+    assert test.get_contact(0).get_node0() == sphere
+    assert test.get_contact(0).get_node1() == heightfield
+
+    # Increment sphere's Z coordinate, no longer colliding
+    np1.set_pos(0, 0, 2)
+    test = world.contact_test_pair(sphere, heightfield)
+    assert test.get_num_contacts() == 0