character_collision.cpp

Go to the documentation of this file.

// 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"

class CharacterCollision : public Test
{
public:
        CharacterCollision()
        {
                // Ground body
                {
                        b2BodyDef bd;
                        b2Body* ground = m_world->CreateBody(&bd);

                        b2EdgeShape shape;
                        shape.SetTwoSided(b2Vec2(-20.0f, 0.0f), b2Vec2(20.0f, 0.0f));
                        ground->CreateFixture(&shape, 0.0f);
                }

                // Collinear edges with no adjacency information.
                // This shows the problematic case where a box shape can hit
                // an internal vertex.
                {
                        b2BodyDef bd;
                        b2Body* ground = m_world->CreateBody(&bd);

                        b2EdgeShape shape;
                        shape.SetTwoSided(b2Vec2(-8.0f, 1.0f), b2Vec2(-6.0f, 1.0f));
                        ground->CreateFixture(&shape, 0.0f);
                        shape.SetTwoSided(b2Vec2(-6.0f, 1.0f), b2Vec2(-4.0f, 1.0f));
                        ground->CreateFixture(&shape, 0.0f);
                        shape.SetTwoSided(b2Vec2(-4.0f, 1.0f), b2Vec2(-2.0f, 1.0f));
                        ground->CreateFixture(&shape, 0.0f);
                }

                // Chain shape
                {
                        b2BodyDef bd;
                        bd.angle = 0.25f * b2_pi;
                        b2Body* ground = m_world->CreateBody(&bd);

                        b2Vec2 vs[4];
                        vs[0].Set(5.0f, 7.0f);
                        vs[1].Set(6.0f, 8.0f);
                        vs[2].Set(7.0f, 8.0f);
                        vs[3].Set(8.0f, 7.0f);
                        b2ChainShape shape;
                        shape.CreateLoop(vs, 4);
                        ground->CreateFixture(&shape, 0.0f);
                }

                // Square tiles. This shows that adjacency shapes may
                // have non-smooth collision. There is no solution
                // to this problem.
                {
                        b2BodyDef bd;
                        b2Body* ground = m_world->CreateBody(&bd);

                        b2PolygonShape shape;
                        shape.SetAsBox(1.0f, 1.0f, b2Vec2(4.0f, 3.0f), 0.0f);
                        ground->CreateFixture(&shape, 0.0f);
                        shape.SetAsBox(1.0f, 1.0f, b2Vec2(6.0f, 3.0f), 0.0f);
                        ground->CreateFixture(&shape, 0.0f);
                        shape.SetAsBox(1.0f, 1.0f, b2Vec2(8.0f, 3.0f), 0.0f);
                        ground->CreateFixture(&shape, 0.0f);
                }

                // Square made from an edge loop. Collision should be smooth.
                {
                        b2BodyDef bd;
                        b2Body* ground = m_world->CreateBody(&bd);

                        b2Vec2 vs[4];
                        vs[0].Set(-1.0f, 3.0f);
                        vs[1].Set(1.0f, 3.0f);
                        vs[2].Set(1.0f, 5.0f);
                        vs[3].Set(-1.0f, 5.0f);
                        b2ChainShape shape;
                        shape.CreateLoop(vs, 4);
                        ground->CreateFixture(&shape, 0.0f);
                }

                // Edge loop. Collision should be smooth.
                {
                        b2BodyDef bd;
                        bd.position.Set(-10.0f, 4.0f);
                        b2Body* ground = m_world->CreateBody(&bd);

                        b2Vec2 vs[10];
                        vs[0].Set(0.0f, 0.0f);
                        vs[1].Set(6.0f, 0.0f);
                        vs[2].Set(6.0f, 2.0f);
                        vs[3].Set(4.0f, 1.0f);
                        vs[4].Set(2.0f, 2.0f);
                        vs[5].Set(0.0f, 2.0f);
                        vs[6].Set(-2.0f, 2.0f);
                        vs[7].Set(-4.0f, 3.0f);
                        vs[8].Set(-6.0f, 2.0f);
                        vs[9].Set(-6.0f, 0.0f);
                        b2ChainShape shape;
                        shape.CreateLoop(vs, 10);
                        ground->CreateFixture(&shape, 0.0f);
                }

                // Square character 1
                {
                        b2BodyDef bd;
                        bd.position.Set(-3.0f, 8.0f);
                        bd.type = b2_dynamicBody;
                        bd.fixedRotation = true;
                        bd.allowSleep = false;

                        b2Body* body = m_world->CreateBody(&bd);

                        b2PolygonShape shape;
                        shape.SetAsBox(0.5f, 0.5f);

                        b2FixtureDef fd;
                        fd.shape = &shape;
                        fd.density = 20.0f;
                        body->CreateFixture(&fd);
                }

                // Square character 2
                {
                        b2BodyDef bd;
                        bd.position.Set(-5.0f, 5.0f);
                        bd.type = b2_dynamicBody;
                        bd.fixedRotation = true;
                        bd.allowSleep = false;

                        b2Body* body = m_world->CreateBody(&bd);

                        b2PolygonShape shape;
                        shape.SetAsBox(0.25f, 0.25f);

                        b2FixtureDef fd;
                        fd.shape = &shape;
                        fd.density = 20.0f;
                        body->CreateFixture(&fd);
                }

                // Hexagon character
                {
                        b2BodyDef bd;
                        bd.position.Set(-5.0f, 8.0f);
                        bd.type = b2_dynamicBody;
                        bd.fixedRotation = true;
                        bd.allowSleep = false;

                        b2Body* body = m_world->CreateBody(&bd);

                        float angle = 0.0f;
                        float delta = b2_pi / 3.0f;
                        b2Vec2 vertices[6];
                        for (int32 i = 0; i < 6; ++i)
                        {
                                vertices[i].Set(0.5f * cosf(angle), 0.5f * sinf(angle));
                                angle += delta;
                        }

                        b2PolygonShape shape;
                        shape.Set(vertices, 6);

                        b2FixtureDef fd;
                        fd.shape = &shape;
                        fd.density = 20.0f;
                        body->CreateFixture(&fd);
                }

                // Circle character
                {
                        b2BodyDef bd;
                        bd.position.Set(3.0f, 5.0f);
                        bd.type = b2_dynamicBody;
                        bd.fixedRotation = true;
                        bd.allowSleep = false;

                        b2Body* body = m_world->CreateBody(&bd);

                        b2CircleShape shape;
                        shape.m_radius = 0.5f;

                        b2FixtureDef fd;
                        fd.shape = &shape;
                        fd.density = 20.0f;
                        body->CreateFixture(&fd);
                }

                // Circle character
                {
                        b2BodyDef bd;
                        bd.position.Set(-7.0f, 6.0f);
                        bd.type = b2_dynamicBody;
                        bd.allowSleep = false;

                        m_character = m_world->CreateBody(&bd);

                        b2CircleShape shape;
                        shape.m_radius = 0.25f;

                        b2FixtureDef fd;
                        fd.shape = &shape;
                        fd.density = 20.0f;
                        fd.friction = 1.0f;
                        m_character->CreateFixture(&fd);
                }
        }

        void Step(Settings& settings) override
        {
                b2Vec2 v = m_character->GetLinearVelocity();
                v.x = -5.0f;
                m_character->SetLinearVelocity(v);

                Test::Step(settings);
                g_debugDraw.DrawString(5, m_textLine, "This tests various character collision shapes.");
                m_textLine += m_textIncrement;
                g_debugDraw.DrawString(5, m_textLine, "Limitation: square and hexagon can snag on aligned boxes.");
                m_textLine += m_textIncrement;
                g_debugDraw.DrawString(5, m_textLine, "Feature: edge chains have smooth collision inside and out.");
                m_textLine += m_textIncrement;
        }

        static Test* Create()
        {
                return new CharacterCollision;
        }

        b2Body* m_character;
};

static int testIndex = RegisterTest("Examples", "Character Collision", CharacterCollision::Create);