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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);
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