[SDL] SDL Box2D Collision - Box2D 충돌

충돌을 감지하고 어떤 오브젝트가 충돌했는지 확인해 보자.

 

#include <iostream>
#include "SDL.h"
#include "box2d/box2d.h"
 
int main(int argc, char* argv[]) {
    SDL_Init(SDL_INIT_VIDEO);
    SDL_Window* window = SDL_CreateWindow("SDL Test", SDL_WINDOWPOS_UNDEFINED,
        SDL_WINDOWPOS_UNDEFINED, 640, 480, SDL_WINDOW_RESIZABLE);
    SDL_Renderer* renderer = SDL_CreateRenderer(window, -1, 0);
    SDL_Surface* playerSurface = SDL_LoadBMP("player.bmp");
    SDL_Texture* texture = SDL_CreateTextureFromSurface(renderer, playerSurface);
 
    // World 정의
    b2Vec2 gravity(0.0f, 9.8f);
    b2World world(gravity);
 
    // Player 정의
    b2BodyDef playerBodyDef;
    playerBodyDef.type = b2_dynamicBody;
    playerBodyDef.position.Set(0.0f, 0.0f);
    playerBodyDef.linearVelocity = b2Vec2(50.0f, 0.0f);
    playerBodyDef.angularVelocity = 0.2f;
    b2Body* playerBody = world.CreateBody(&playerBodyDef);
    b2PolygonShape dynamicBox;
    dynamicBox.SetAsBox((float)playerSurface->w / 2, (float)playerSurface->h / 2);
    b2FixtureDef fixtureDef;
    fixtureDef.shape = &dynamicBox;
    fixtureDef.density = 1.0f;
    fixtureDef.friction = 0.3f;
    fixtureDef.restitution = 0.5f;
    playerBody->CreateFixture(&fixtureDef);
    // Player 유저 정보
    const char* playerName = "Player";
    playerBody->GetUserData().pointer = reinterpret_cast<uintptr_t>(playerName);
 
    // Ground 정의
    b2BodyDef groundBodyDef;
    groundBodyDef.position.Set(0.0f, 400.0f);
    b2Body* groundBody = world.CreateBody(&groundBodyDef);
    b2PolygonShape groundBox;
    groundBox.SetAsBox(500.0f, 0.0f);
    SDL_Rect groundRect = { 0, 400, 500, 10 };
    groundBody->CreateFixture(&groundBox, 0.0f);
    // Ground 유저 정보
    const char* groundName = "Ground";
    groundBody->GetUserData().pointer = reinterpret_cast<uintptr_t>(groundName);
 
    // Wall 정의
    b2BodyDef wallBodyDef;
    wallBodyDef.position.Set(300.0f, 0.0f);
    b2Body* wallBody = world.CreateBody(&wallBodyDef);
    b2PolygonShape wallBox;
    wallBox.SetAsBox(0.0f, 480.0f);
    SDL_Rect wallRect = { 300, 0, 10, 480 };
    wallBody->CreateFixture(&wallBox, 0.0f);
    // Wall 유저 정보
    const char* wallName = "Wall";
    wallBody->GetUserData().pointer = reinterpret_cast<uintptr_t>(wallName);
 
    float timeStep = 1.0f / 500.0f;
    int velocityIterations = 6;
    int positionIterations = 2;
 
    SDL_Event event;
    bool quit = false;
 
    while (!quit) {
        while (SDL_PollEvent(&event)) {
            switch (event.type) {
            case SDL_QUIT:
                quit = true;
                break;
            case SDL_KEYDOWN:
                printf("Key pressed: %s\n", SDL_GetKeyName(event.key.keysym.sym));
                if (event.key.keysym.sym == SDLK_SPACE) {
                    playerBody->SetTransform(b2Vec2(0.0f, 0.0f), 0.0f);
                    playerBody->SetLinearVelocity(b2Vec2(50.0f, 0.0f));
                    playerBody->SetAngularVelocity(0.2f);
                }
                if (event.key.keysym.sym == SDLK_ESCAPE)
                    quit = true;
                break;
 
            default:
                break;
            }
        }
 
        world.Step(timeStep, velocityIterations, positionIterations);
 
        for (b2Contact* c = world.GetContactList(); c; c = c->GetNext())
        {
            if (c->IsTouching()) {
                printf("FixtureA: %s\n", (char*)(c->GetFixtureA()->GetBody()->GetUserData().pointer));
                printf("FixtureB: %s\n", (char*)(c->GetFixtureB()->GetBody()->GetUserData().pointer));
                printf("Count: %d\n", c->GetManifold()->pointCount);
            }
            //if (c->GetFixtureA()->IsSensor() == false)
                //c->GetFixtureA()->SetSensor(true);
        }
        // A very important point to note if you do this, is that the existence of a contact in these
        // lists does not mean that the two fixtures of the contact are actually touching - it only
        // means their AABBs are touching. If you want to know if the fixtures themselves are really
        // touching you can use c->IsTouching() to check.
 
        SDL_SetRenderDrawColor(renderer, 255, 255, 255, SDL_ALPHA_OPAQUE);
        SDL_RenderClear(renderer);
 
        // Ground 그리기
        SDL_SetRenderDrawColor(renderer, 220, 140, 20, SDL_ALPHA_OPAQUE);
        SDL_RenderFillRect(renderer, &groundRect);
 
        // Wall 그리기
        SDL_SetRenderDrawColor(renderer, 64, 64, 64, SDL_ALPHA_OPAQUE);
        SDL_RenderFillRect(renderer, &wallRect);
 
        // Player 그리기        
        b2Vec2 playerPosition = playerBody->GetPosition();
        SDL_Rect destRect = { (int)playerPosition.x - playerSurface->w / 2,
            (int)playerPosition.y - playerSurface->h / 2, playerSurface->w, playerSurface->h };
        SDL_RendererFlip flip = SDL_FLIP_NONE;
        float angle = playerBody->GetAngle() * (180 / (float)M_PI);
 
        SDL_RenderCopyEx(renderer, texture, NULL, &destRect, angle, NULL, flip);
        SDL_RenderPresent(renderer);
    }
 
    SDL_DestroyTexture(texture);
    SDL_FreeSurface(playerSurface);
    SDL_DestroyRenderer(renderer);
    SDL_DestroyWindow(window);
    SDL_Quit();
 
    return 0;
}

 

코드를 작성하고 빌드한다.

오브젝트 UserData 설정시 SetUserData()를 사용하면 안된다는 것에 주의한다. (아래 참고 참조)

 

실행하면 Player 오브젝트가 던져지고 벽과 바닥에 부딪힌다.

 

부딪힌 오브젝트와 몇 개의 포인트에서 충돌이 발생한지 확인 할 수 있다.

 

바닥에 완전히 정지하면 2개 포인트에서 충돌이 계속 발생한다.

 

※ 참고

Box2D Collision Module

Box2D Dynamic Module - Contacts

Box2D UserData

Box2D SetUserData()