Add initial prototype.

3-mid/physics/implement/box2d/contrib/unit-test/hello_world.cpp

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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"
+#define DOCTEST_CONFIG_IMPLEMENT_WITH_MAIN
+#include "doctest.h"
+#include <stdio.h>
+
+// This is a simple example of building and running a simulation
+// using Box2D. Here we create a large ground box and a small dynamic
+// box.
+// There are no graphics for this example. Box2D is meant to be used
+// with your rendering engine in your game engine.
+DOCTEST_TEST_CASE("hello world")
+{
+	// Define the gravity vector.
+	b2Vec2 gravity(0.0f, -10.0f);
+
+	// Construct a world object, which will hold and simulate the rigid bodies.
+	b2World world(gravity);
+
+	// Define the ground body.
+	b2BodyDef groundBodyDef;
+	groundBodyDef.position.Set(0.0f, -10.0f);
+
+	// Call the body factory which allocates memory for the ground body
+	// from a pool and creates the ground box shape (also from a pool).
+	// The body is also added to the world.
+	b2Body* groundBody = world.CreateBody(&groundBodyDef);
+
+	// Define the ground box shape.
+	b2PolygonShape groundBox;
+
+	// The extents are the half-widths of the box.
+	groundBox.SetAsBox(50.0f, 10.0f);
+
+	// Add the ground fixture to the ground body.
+	groundBody->CreateFixture(&groundBox, 0.0f);
+
+	// Define the dynamic body. We set its position and call the body factory.
+	b2BodyDef bodyDef;
+	bodyDef.type = b2_dynamicBody;
+	bodyDef.position.Set(0.0f, 4.0f);
+	b2Body* body = world.CreateBody(&bodyDef);
+
+	// Define another box shape for our dynamic body.
+	b2PolygonShape dynamicBox;
+	dynamicBox.SetAsBox(1.0f, 1.0f);
+
+	// Define the dynamic body fixture.
+	b2FixtureDef fixtureDef;
+	fixtureDef.shape = &dynamicBox;
+
+	// Set the box density to be non-zero, so it will be dynamic.
+	fixtureDef.density = 1.0f;
+
+	// Override the default friction.
+	fixtureDef.friction = 0.3f;
+
+	// Add the shape to the body.
+	body->CreateFixture(&fixtureDef);
+
+	// Prepare for simulation. Typically we use a time step of 1/60 of a
+	// second (60Hz) and 10 iterations. This provides a high quality simulation
+	// in most game scenarios.
+	float timeStep = 1.0f / 60.0f;
+	int32 velocityIterations = 6;
+	int32 positionIterations = 2;
+
+	b2Vec2 position = body->GetPosition();
+	float angle = body->GetAngle();
+
+	// This is our little game loop.
+	for (int32 i = 0; i < 60; ++i)
+	{
+		// Instruct the world to perform a single step of simulation.
+		// It is generally best to keep the time step and iterations fixed.
+		world.Step(timeStep, velocityIterations, positionIterations);
+
+		// Now print the position and angle of the body.
+		position = body->GetPosition();
+		angle = body->GetAngle();
+
+		printf("%4.2f %4.2f %4.2f\n", position.x, position.y, angle);
+	}
+
+	// When the world destructor is called, all bodies and joints are freed. This can
+	// create orphaned pointers, so be careful about your world management.
+
+	CHECK(b2Abs(position.x) < 0.01f);
+	CHECK(b2Abs(position.y - 1.01f) < 0.01f);
+	CHECK(b2Abs(angle) < 0.01f);
+}