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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 "box2d/box2d.h"
#include "doctest.h"
#include <stdio.h>
DOCTEST_TEST_CASE("joint reactions")
{
b2Vec2 gravity(0, -10.0f);
b2World world = b2World(gravity);
b2BodyDef bodyDef;
b2Body* ground = world.CreateBody(&bodyDef);
b2CircleShape circle;
circle.m_radius = 1.0f;
b2FixtureDef fixtureDef;
// Disable collision
fixtureDef.filter.maskBits = 0;
fixtureDef.density = 1.0f;
fixtureDef.shape = &circle;
bodyDef.type = b2_dynamicBody;
bodyDef.position.Set(-2.0f, 3.0f);
b2Body* bodyA = world.CreateBody(&bodyDef);
b2Body* bodyB = world.CreateBody(&bodyDef);
b2Body* bodyC = world.CreateBody(&bodyDef);
b2MassData massData;
circle.ComputeMass(&massData, fixtureDef.density);
const float mg = massData.mass * gravity.y;
bodyA->CreateFixture(&fixtureDef);
bodyB->CreateFixture(&fixtureDef);
bodyC->CreateFixture(&fixtureDef);
b2DistanceJointDef distanceJointDef;
distanceJointDef.Initialize(ground, bodyA, bodyDef.position + b2Vec2(0.0f, 4.0f), bodyDef.position);
distanceJointDef.minLength = distanceJointDef.length;
distanceJointDef.maxLength = distanceJointDef.length;
b2PrismaticJointDef prismaticJointDef;
prismaticJointDef.Initialize(ground, bodyB, bodyDef.position, b2Vec2(1.0f, 0.0f));
b2RevoluteJointDef revoluteJointDef;
revoluteJointDef.Initialize(ground, bodyC, bodyDef.position);
b2DistanceJoint* distanceJoint = (b2DistanceJoint*)world.CreateJoint(&distanceJointDef);
b2PrismaticJoint* prismaticJoint = (b2PrismaticJoint*)world.CreateJoint(&prismaticJointDef);
b2RevoluteJoint* revoluteJoint = (b2RevoluteJoint*)world.CreateJoint(&revoluteJointDef);
const float timeStep = 1.f / 60.f;
const float invTimeStep = 60.0f;
const int32 velocityIterations = 6;
const int32 positionIterations = 2;
world.Step(timeStep, velocityIterations, positionIterations);
const float tol = 1e-5f;
{
b2Vec2 F = distanceJoint->GetReactionForce(invTimeStep);
float T = distanceJoint->GetReactionTorque(invTimeStep);
CHECK(F.x == 0.0f);
CHECK(b2Abs(F.y + mg) < tol);
CHECK(T == 0.0f);
}
{
b2Vec2 F = prismaticJoint->GetReactionForce(invTimeStep);
float T = prismaticJoint->GetReactionTorque(invTimeStep);
CHECK(F.x == 0.0f);
CHECK(b2Abs(F.y + mg) < tol);
CHECK(T == 0.0f);
}
{
b2Vec2 F = revoluteJoint->GetReactionForce(invTimeStep);
float T = revoluteJoint->GetReactionTorque(invTimeStep);
CHECK(F.x == 0.0f);
CHECK(b2Abs(F.y + mg) < tol);
CHECK(T == 0.0f);
}
}
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