Add initial prototype.

3-mid/physics/implement/box2d/contrib/testbed/tests/wrecking_ball.cpp

@@ -0,0 +1,165 @@
+// 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);