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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"
#include "imgui/imgui.h"
/// This test shows how a distance joint can be used to stabilize a chain of
/// bodies with a heavy payload. Notice that the distance joint just prevents
/// excessive stretching and has no other effect.
/// By disabling the distance 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 WreckingBall : public Test
{
public:
WreckingBall()
{
b2Body* ground = NULL;
{
b2BodyDef bd;
ground = m_world->CreateBody(&bd);
b2EdgeShape shape;
shape.SetTwoSided(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 float y = 15.0f;
m_distanceJointDef.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)
{
bd.position.Set(1.0f * i, y);
bd.angularDamping = 0.4f;
}
b2Body* body = m_world->CreateBody(&bd);
if (i == N - 1)
{
b2CircleShape circleShape;
circleShape.m_radius = 1.5f;
b2FixtureDef sfd;
sfd.shape = &circleShape;
sfd.density = 100.0f;
sfd.filter.categoryBits = 0x0002;
body->CreateFixture(&sfd);
}
else
{
body->CreateFixture(&fd);
}
b2Vec2 anchor(float(i), y);
jd.Initialize(prevBody, body, anchor);
m_world->CreateJoint(&jd);
prevBody = body;
}
m_distanceJointDef.localAnchorB.SetZero();
float extraLength = 0.01f;
m_distanceJointDef.minLength = 0.0f;
m_distanceJointDef.maxLength = N - 1.0f + extraLength;
m_distanceJointDef.bodyB = prevBody;
}
{
m_distanceJointDef.bodyA = ground;
m_distanceJoint = m_world->CreateJoint(&m_distanceJointDef);
m_stabilize = true;
}
}
void UpdateUI() override
{
ImGui::SetNextWindowPos(ImVec2(10.0f, 100.0f));
ImGui::SetNextWindowSize(ImVec2(200.0f, 100.0f));
ImGui::Begin("Wrecking Ball Controls", nullptr, ImGuiWindowFlags_NoMove | ImGuiWindowFlags_NoResize);
if (ImGui::Checkbox("Stabilize", &m_stabilize))
{
if (m_stabilize == true && m_distanceJoint == nullptr)
{
m_distanceJoint = m_world->CreateJoint(&m_distanceJointDef);
}
else if (m_stabilize == false && m_distanceJoint != nullptr)
{
m_world->DestroyJoint(m_distanceJoint);
m_distanceJoint = nullptr;
}
}
ImGui::End();
}
void Step(Settings& settings) override
{
Test::Step(settings);
if (m_distanceJoint)
{
g_debugDraw.DrawString(5, m_textLine, "Distance Joint ON");
}
else
{
g_debugDraw.DrawString(5, m_textLine, "Distance Joint OFF");
}
m_textLine += m_textIncrement;
}
static Test* Create()
{
return new WreckingBall;
}
b2DistanceJointDef m_distanceJointDef;
b2Joint* m_distanceJoint;
bool m_stabilize;
};
static int testIndex = RegisterTest("Examples", "Wrecking Ball", WreckingBall::Create);
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