JoltPhysics/Samples/Tests/Constraints/RackAndPinionConstraintTest.cpp

// Jolt Physics Library (https://github.com/jrouwe/JoltPhysics)
// SPDX-FileCopyrightText: 2021 Jorrit Rouwe
// SPDX-License-Identifier: MIT

#include <TestFramework.h>

#include <Tests/Constraints/RackAndPinionConstraintTest.h>
#include <Jolt/Physics/Collision/Shape/BoxShape.h>
#include <Jolt/Physics/Collision/Shape/CylinderShape.h>
#include <Jolt/Physics/Collision/Shape/ConvexHullShape.h>
#include <Jolt/Physics/Collision/Shape/StaticCompoundShape.h>
#include <Jolt/Physics/Collision/GroupFilterTable.h>
#include <Jolt/Physics/Constraints/HingeConstraint.h>
#include <Jolt/Physics/Constraints/SliderConstraint.h>
#include <Jolt/Physics/Constraints/RackAndPinionConstraint.h>
#include <Jolt/Physics/Body/BodyCreationSettings.h>
#include <Layers.h>

JPH_IMPLEMENT_RTTI_VIRTUAL(RackAndPinionConstraintTest)
{
	JPH_ADD_BASE_CLASS(RackAndPinionConstraintTest, Test)
}

void RackAndPinionConstraintTest::Initialize()
{
	// Floor
	CreateFloor();

	constexpr float cGearRadius = 0.5f;
	constexpr float cGearHalfWidth = 0.05f;
	constexpr int cGearNumTeeth = 100;

	constexpr float cRackLength = 10.0f;
	constexpr float cRackHalfHeight = 0.1f;
	constexpr float cRackHalfWidth = 0.05f;
	constexpr int cRackNumTeeth = int(cRackLength * cGearNumTeeth / (2.0f * JPH_PI * cGearRadius));

	constexpr float cToothThicknessBottom = 0.01f;
	constexpr float cToothThicknessTop = 0.005f;
	constexpr float cToothHeight = 0.02f;

	// Create a tooth
	Array<Vec3> tooth_points = {
		Vec3(0, cGearHalfWidth, cToothThicknessBottom),
		Vec3(0, -cGearHalfWidth, cToothThicknessBottom),
		Vec3(0, cGearHalfWidth, -cToothThicknessBottom),
		Vec3(0, -cGearHalfWidth, -cToothThicknessBottom),
		Vec3(cToothHeight, -cGearHalfWidth, cToothThicknessTop),
		Vec3(cToothHeight, cGearHalfWidth, cToothThicknessTop),
		Vec3(cToothHeight, -cGearHalfWidth, -cToothThicknessTop),
		Vec3(cToothHeight, cGearHalfWidth, -cToothThicknessTop),
	};
	ConvexHullShapeSettings tooth_settings(tooth_points);
	tooth_settings.SetEmbedded();

	// Create gear
	CylinderShapeSettings gear_cylinder(cGearHalfWidth, cGearRadius);
	gear_cylinder.SetEmbedded();

	StaticCompoundShapeSettings gear_settings;
	gear_settings.SetEmbedded();

	gear_settings.AddShape(Vec3::sZero(), Quat::sIdentity(), &gear_cylinder);
	for (int i = 0; i < cGearNumTeeth; ++i)
	{
		Quat rotation = Quat::sRotation(Vec3::sAxisY(), 2.0f * JPH_PI * i / cGearNumTeeth);
		gear_settings.AddShape(rotation * Vec3(cGearRadius, 0, 0), rotation, &tooth_settings);
	}

	RVec3 gear_initial_p(0, 2.0f, 0);
	Quat gear_initial_r = Quat::sRotation(Vec3::sAxisX(), 0.5f * JPH_PI);
	Body *gear = mBodyInterface->CreateBody(BodyCreationSettings(&gear_settings, gear_initial_p, gear_initial_r, EMotionType::Dynamic, Layers::MOVING));
	mBodyInterface->AddBody(gear->GetID(), EActivation::Activate);

	// Create rack
	BoxShapeSettings rack_box(Vec3(cRackHalfHeight, cRackHalfWidth, 0.5f * cRackLength), 0.0f);
	rack_box.SetEmbedded();

	StaticCompoundShapeSettings rack_settings;
	rack_settings.SetEmbedded();

	rack_settings.AddShape(Vec3::sZero(), Quat::sIdentity(), &rack_box);
	for (int i = 0; i < cRackNumTeeth; ++i)
		rack_settings.AddShape(Vec3(cRackHalfHeight, 0, -0.5f * cRackLength + (i + 0.5f) * cRackLength / cRackNumTeeth), Quat::sIdentity(), &tooth_settings);

	RVec3 slider_initial_p = gear_initial_p - Vec3(0, cGearRadius + cRackHalfHeight + cToothHeight, 0);
	Quat slider_initial_r = Quat::sRotation(Vec3::sAxisZ(), 0.5f * JPH_PI) * gear_initial_r;
	Body *rack = mBodyInterface->CreateBody(BodyCreationSettings(&rack_settings, slider_initial_p, slider_initial_r, EMotionType::Dynamic, Layers::MOVING));
	mBodyInterface->AddBody(rack->GetID(), EActivation::Activate);

	// Create a hinge for the gear
	HingeConstraintSettings hinge;
	hinge.mPoint1 = hinge.mPoint2 = gear_initial_p;
	hinge.mHingeAxis1 = hinge.mHingeAxis2 = Vec3::sAxisZ();
	hinge.mNormalAxis1 = hinge.mNormalAxis2 = Vec3::sAxisX();
	Constraint *hinge_constraint = hinge.Create(Body::sFixedToWorld, *gear);
	mPhysicsSystem->AddConstraint(hinge_constraint);

	// Create a slider for the rack
	SliderConstraintSettings slider;
	slider.mPoint1 = slider.mPoint2 = gear_initial_p;
	slider.mSliderAxis1 = slider.mSliderAxis2 = Vec3::sAxisX();
	slider.mNormalAxis1 = slider.mNormalAxis2 = Vec3::sAxisZ();
	slider.mLimitsMin = -0.5f * cRackLength;
	slider.mLimitsMax = 0.5f * cRackLength;
	Constraint *slider_constraint = slider.Create(Body::sFixedToWorld, *rack);
	mPhysicsSystem->AddConstraint(slider_constraint);

	// Disable collision between rack and gear (we want the rack and pinion constraint to take care of the relative movement)
	Ref<GroupFilterTable> group_filter = new GroupFilterTable(2);
	group_filter->DisableCollision(0, 1);
	gear->SetCollisionGroup(CollisionGroup(group_filter, 0, 0));
	rack->SetCollisionGroup(CollisionGroup(group_filter, 0, 1));

	// Create rack and pinion constraint to constrain the two bodies
	RackAndPinionConstraintSettings randp;
	randp.mHingeAxis = hinge.mHingeAxis1;
	randp.mSliderAxis = slider.mSliderAxis2;
	randp.SetRatio(cRackNumTeeth, cRackLength, cGearNumTeeth);
	RackAndPinionConstraint *randp_constraint = static_cast<RackAndPinionConstraint *>(randp.Create(*gear, *rack));
	randp_constraint->SetConstraints(hinge_constraint, slider_constraint);
	mPhysicsSystem->AddConstraint(randp_constraint);

	// Give the gear a spin
	gear->SetAngularVelocity(Vec3(0, 0, 6.0f));
}