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/*
* Copyright (c) 2006-2010 Erin Catto http://www.box2d.org
*
* This software is provided 'as-is', without any express or implied
* warranty. In no event will the authors be held liable for any damages
* arising from the use of this software.
* Permission is granted to anyone to use this software for any purpose,
* including commercial applications, and to alter it and redistribute it
* freely, subject to the following restrictions:
* 1. The origin of this software must not be misrepresented; you must not
* claim that you wrote the original software. If you use this software
* in a product, an acknowledgment in the product documentation would be
* appreciated but is not required.
* 2. Altered source versions must be plainly marked as such, and must not be
* misrepresented as being the original software.
* 3. This notice may not be removed or altered from any source distribution.
*/
#ifndef ROPE_JOINT_H
#define ROPE_JOINT_H
/// This test shows how a rope joint can be used to stabilize a chain of
/// bodies with a heavy payload. Notice that the rope joint just prevents
/// excessive stretching and has no other effect.
/// By disabling the rope joint you can see that the Box2D solver has trouble
/// supporting heavy bodies with light bodies. Try playing around with the
/// densities, time step, and iterations to see how they affect stability.
/// This test also shows how to use contact filtering. Filtering is configured
/// so that the payload does not collide with the chain.
class RopeJoint : public Test
{
public:
RopeJoint()
{
b2Body* ground = NULL;
{
b2BodyDef bd;
ground = m_world->CreateBody(&bd);
b2EdgeShape shape;
shape.Set(b2Vec2(-40.0f, 0.0f), b2Vec2(40.0f, 0.0f));
ground->CreateFixture(&shape, 0.0f);
}
{
b2PolygonShape shape;
shape.SetAsBox(0.5f, 0.125f);
b2FixtureDef fd;
fd.shape = &shape;
fd.density = 20.0f;
fd.friction = 0.2f;
fd.filter.categoryBits = 0x0001;
fd.filter.maskBits = 0xFFFF & ~0x0002;
b2RevoluteJointDef jd;
jd.collideConnected = false;
const int32 N = 10;
const float32 y = 15.0f;
m_ropeDef.localAnchorA.Set(0.0f, y);
b2Body* prevBody = ground;
for (int32 i = 0; i < N; ++i)
{
b2BodyDef bd;
bd.type = b2_dynamicBody;
bd.position.Set(0.5f + 1.0f * i, y);
if (i == N - 1)
{
shape.SetAsBox(1.5f, 1.5f);
fd.density = 100.0f;
fd.filter.categoryBits = 0x0002;
bd.position.Set(1.0f * i, y);
bd.angularDamping = 0.4f;
}
b2Body* body = m_world->CreateBody(&bd);
body->CreateFixture(&fd);
b2Vec2 anchor(float32(i), y);
jd.Initialize(prevBody, body, anchor);
m_world->CreateJoint(&jd);
prevBody = body;
}
m_ropeDef.localAnchorB.SetZero();
float32 extraLength = 0.01f;
m_ropeDef.maxLength = N - 1.0f + extraLength;
m_ropeDef.bodyB = prevBody;
}
{
m_ropeDef.bodyA = ground;
m_rope = m_world->CreateJoint(&m_ropeDef);
}
}
void Keyboard(unsigned char key)
{
switch (key)
{
case 'j':
if (m_rope)
{
m_world->DestroyJoint(m_rope);
m_rope = NULL;
}
else
{
m_rope = m_world->CreateJoint(&m_ropeDef);
}
break;
}
}
void Step(Settings* settings)
{
Test::Step(settings);
m_debugDraw.DrawString(5, m_textLine, "Press (j) to toggle the rope joint.");
m_textLine += 15;
if (m_rope)
{
m_debugDraw.DrawString(5, m_textLine, "Rope ON");
}
else
{
m_debugDraw.DrawString(5, m_textLine, "Rope OFF");
}
m_textLine += 15;
}
static Test* Create()
{
return new RopeJoint;
}
b2RopeJointDef m_ropeDef;
b2Joint* m_rope;
};
#endif
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