embedded_libs/box2d-2.4.1/testbed/tests/apply_force.cpp

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// MIT License

// Copyright (c) 2019 Erin Catto

// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:

// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.

// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.

#include "test.h"

// This test shows how to apply forces and torques to a body.
// It also shows how to use the friction joint that can be useful
// for overhead games.
class ApplyForce : public Test
{
public:
	ApplyForce()
	{
		m_world->SetGravity(b2Vec2(0.0f, 0.0f));

		const float k_restitution = 0.4f;

		b2Body* ground;
		{
			b2BodyDef bd;
			bd.position.Set(0.0f, 20.0f);
			ground = m_world->CreateBody(&bd);

			b2EdgeShape shape;

			b2FixtureDef sd;
			sd.shape = &shape;
			sd.density = 0.0f;
			sd.restitution = k_restitution;

			// Left vertical
			shape.SetTwoSided(b2Vec2(-20.0f, -20.0f), b2Vec2(-20.0f, 20.0f));
			ground->CreateFixture(&sd);

			// Right vertical
			shape.SetTwoSided(b2Vec2(20.0f, -20.0f), b2Vec2(20.0f, 20.0f));
			ground->CreateFixture(&sd);

			// Top horizontal
			shape.SetTwoSided(b2Vec2(-20.0f, 20.0f), b2Vec2(20.0f, 20.0f));
			ground->CreateFixture(&sd);

			// Bottom horizontal
			shape.SetTwoSided(b2Vec2(-20.0f, -20.0f), b2Vec2(20.0f, -20.0f));
			ground->CreateFixture(&sd);
		}

		{
			b2Transform xf1;
			xf1.q.Set(0.3524f * b2_pi);
			xf1.p = xf1.q.GetXAxis();

			b2Vec2 vertices[3];
			vertices[0] = b2Mul(xf1, b2Vec2(-1.0f, 0.0f));
			vertices[1] = b2Mul(xf1, b2Vec2(1.0f, 0.0f));
			vertices[2] = b2Mul(xf1, b2Vec2(0.0f, 0.5f));
			
			b2PolygonShape poly1;
			poly1.Set(vertices, 3);

			b2FixtureDef sd1;
			sd1.shape = &poly1;
			sd1.density = 2.0f;

			b2Transform xf2;
			xf2.q.Set(-0.3524f * b2_pi);
			xf2.p = -xf2.q.GetXAxis();

			vertices[0] = b2Mul(xf2, b2Vec2(-1.0f, 0.0f));
			vertices[1] = b2Mul(xf2, b2Vec2(1.0f, 0.0f));
			vertices[2] = b2Mul(xf2, b2Vec2(0.0f, 0.5f));
			
			b2PolygonShape poly2;
			poly2.Set(vertices, 3);

			b2FixtureDef sd2;
			sd2.shape = &poly2;
			sd2.density = 2.0f;

			b2BodyDef bd;
			bd.type = b2_dynamicBody;

			bd.position.Set(0.0f, 3.0);
			bd.angle = b2_pi;
			bd.allowSleep = false;
			m_body = m_world->CreateBody(&bd);
			m_body->CreateFixture(&sd1);
			m_body->CreateFixture(&sd2);

			float gravity = 10.0f;
			float I = m_body->GetInertia();
			float mass = m_body->GetMass();

			// Compute an effective radius that can be used to
			// set the max torque for a friction joint
			// For a circle: I = 0.5 * m * r * r ==> r = sqrt(2 * I / m)
			float radius = b2Sqrt(2.0f * I / mass);

			b2FrictionJointDef jd;
			jd.bodyA = ground;
			jd.bodyB = m_body;
			jd.localAnchorA.SetZero();
			jd.localAnchorB = m_body->GetLocalCenter();
			jd.collideConnected = true;
			jd.maxForce = 0.5f * mass * gravity;
			jd.maxTorque = 0.2f * mass * radius * gravity;

			m_world->CreateJoint(&jd);
		}

		{
			b2PolygonShape shape;
			shape.SetAsBox(0.5f, 0.5f);

			b2FixtureDef fd;
			fd.shape = &shape;
			fd.density = 1.0f;
			fd.friction = 0.3f;

			for (int i = 0; i < 10; ++i)
			{
				b2BodyDef bd;
				bd.type = b2_dynamicBody;

				bd.position.Set(0.0f, 7.0f + 1.54f * i);
				b2Body* body = m_world->CreateBody(&bd);

				body->CreateFixture(&fd);

				float gravity = 10.0f;
				float I = body->GetInertia();
				float mass = body->GetMass();

				// For a circle: I = 0.5 * m * r * r ==> r = sqrt(2 * I / m)
				float radius = b2Sqrt(2.0f * I / mass);

				b2FrictionJointDef jd;
				jd.localAnchorA.SetZero();
				jd.localAnchorB.SetZero();
				jd.bodyA = ground;
				jd.bodyB = body;
				jd.collideConnected = true;
				jd.maxForce = mass * gravity;
				jd.maxTorque = 0.1f * mass * radius * gravity;

				m_world->CreateJoint(&jd);
			}
		}
	}

	void Step(Settings& settings) override
	{
		g_debugDraw.DrawString(5, m_textLine, "Forward (W), Turn (A) and (D)");
		m_textLine += m_textIncrement;

		if (glfwGetKey(g_mainWindow, GLFW_KEY_W) == GLFW_PRESS)
		{
			b2Vec2 f = m_body->GetWorldVector(b2Vec2(0.0f, -50.0f));
			b2Vec2 p = m_body->GetWorldPoint(b2Vec2(0.0f, 3.0f));
			m_body->ApplyForce(f, p, true);
		}

		if (glfwGetKey(g_mainWindow, GLFW_KEY_A) == GLFW_PRESS)
		{
			m_body->ApplyTorque(10.0f, true);
		}

		if (glfwGetKey(g_mainWindow, GLFW_KEY_D) == GLFW_PRESS)
		{
			m_body->ApplyTorque(-10.0f, true);
		}

		Test::Step(settings);
	}

	static Test* Create()
	{
		return new ApplyForce;
	}

	b2Body* m_body;
};

static int testIndex = RegisterTest("Forces", "Apply Force", ApplyForce::Create);