tests: add unit tests for particle systems and #769 in particular

Co-authored-by: rdb <git@rdb.name>

tests/particles/test_particlesystem.py

@@ -0,0 +1,103 @@
+from panda3d.core import NodePath, PandaNode
+from direct.particles.ParticleEffect import ParticleEffect
+from direct.particles.Particles import Particles
+
+
+def test_particle_birth_rate():
+    # Tests a system with a standard birth rate of 0.5, that it is
+    # indeed birthing at that rate.  It serves as a control for the
+    # next test as well.
+    system = Particles("testSystem", 2)
+
+    system.set_render_parent(NodePath(PandaNode("test")))
+    system.set_spawn_render_node_path(NodePath(PandaNode("test")))
+
+    assert system.get_birth_rate() == 0.5
+    assert system.get_tics_since_birth() == 0
+    assert system.get_living_particles() == 0
+
+    system.update(0.6)
+    assert system.get_living_particles() == 1
+
+    system.update(0.5)
+    assert system.get_living_particles() == 2
+
+    # Should still be 2, since the pool size was 2.
+    system.update(0.5)
+    assert system.get_living_particles() == 2
+
+
+def test_particle_soft_start():
+    # Create a particle effect and a particle system.
+    # The effect serves to test the Python-level "soft_start"  method,
+    # while the system serves to test the C++-level "soft_start" method
+    # (via the associated Python "soft_start" method)
+    effect = ParticleEffect()
+    system = Particles("testSystem", 10)
+
+    # Setup some dummy nodes, since it seems to want them
+    system.set_render_parent(NodePath(PandaNode("test")))
+    system.set_spawn_render_node_path(NodePath(PandaNode("test")))
+
+    # Add the system to the effect
+    effect.add_particles(system)
+
+    # Re-assign the system, just to make sure that we have the
+    # right object.
+    system = effect.get_particles_list()[0]
+
+    # First, standard "soft_start"--i.e. without either changing
+    # the birth-rate or applying a delay. This should work as it
+    # used to.
+    effect.soft_start()
+
+    assert system.get_birth_rate() == 0.5
+
+    # Now, check that the pre-existing single-parameter soft-start,
+    # which alters the birth-rate, still does so.
+    system.soft_start(1)
+
+    assert system.get_birth_rate() == 1
+
+    # Next, birth-delaying.
+
+    # Run a standard soft-start, then check that the birth-timer
+    # is zero, as used to be the case on running this command.
+    effect.soft_start()
+
+    assert system.get_tics_since_birth() == 0
+
+    # Run an delayed soft-start via the system, then check that the
+    # birth-timer has the assigned value, and that the birth-rate is
+    # unchanged.
+
+    # (We pass in a birth-rate ("br") of -1 because the related code
+    # checks for a birth-rate greater than 0, I believe. This allows
+    # us to change the delay without affecting the birth-rate.)
+    system.soft_start(br=-1, first_birth_delay=-2)
+
+    assert system.get_birth_rate() == 1
+    assert system.get_tics_since_birth() == 2
+
+    # Now, run a delayed soft-start via the effect, and
+    # again check that the birth-timer has changed as intended,
+    # and the birth-rate hasn't changed at all.
+    effect.soft_start(firstBirthDelay=0.25)
+
+    assert system.get_birth_rate() == 1
+    assert system.get_tics_since_birth() == -0.25
+
+    # Update the system, advancing it far enough that it should
+    # have birthed a particle if not for the delay, but not
+    # so far that it should have birthed a particle >with<
+    # the delay. Check thus that no particles have been birthed.
+    system.update(1)
+
+    assert system.get_living_particles() == 0
+
+    # Update the system again, this time far enough that with the
+    # delay it should have birthed just one particle, and
+    # then check that this is the case.
+    system.update(1)
+
+    assert system.get_living_particles() == 1