[SDL] SDL Box2D Add Collision Shape - Box2D 충돌 감지

한 오브젝트에 여러개의 Shape을 추가해 충돌을 감지해 보자.

XXXShape이나 FixtureDef를 CreateFixture()에 전달하면 충돌 감지기가 추가된다.

 

#include <iostream>
#include "SDL.h"
#include "box2d/box2d.h"
 
class DebugDrawer : public b2Draw
{
public:
    DebugDrawer(SDL_Renderer* renderer) {
        this->renderer = renderer;
    }
private:
    SDL_Renderer* renderer;
    void DrawSolidPolygon(const b2Vec2* vertices, int32 vertexCount, const b2Color& color) {}
    void DrawPoint(const b2Vec2& p, float size, const b2Color& color) {}
    void DrawPolygon(const b2Vec2* vertices, int32 vertexCount, const b2Color& color) {
        SDL_SetRenderDrawColor(renderer, 255, 0, 0, SDL_ALPHA_OPAQUE);
        SDL_FRect* rect = new SDL_FRect{ vertices[0].x, vertices[0].y, vertices[1].x
            - vertices[0].x, vertices[3].y - vertices[0].y };
        SDL_RenderDrawRectF(renderer, rect);
    }
    void DrawCircle(const b2Vec2& center, float radius, const b2Color& color) {}
    void DrawSolidCircle(const b2Vec2& center, float radius, const b2Vec2& axis, const b2Color& color) {}
    void DrawSegment(const b2Vec2& p1, const b2Vec2& p2, const b2Color& color) {}
    void DrawTransform(const b2Transform& xf) {}
};
 
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);
 
    // DebugDraw 정의
    DebugDrawer* debugDrawer = new DebugDrawer(renderer);
    debugDrawer->SetFlags(b2Draw::e_shapeBit | b2Draw::e_jointBit |
        b2Draw::e_centerOfMassBit | b2Draw::e_aabbBit | b2Draw::e_pairBit);
    world.SetDebugDraw(debugDrawer);
 
    // 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);
    // Player에 shape 추가
    b2PolygonShape another;
    another.SetAsBox(10, 40, b2Vec2(0, -60), 0.0f);
    playerBody->CreateFixture(&another, 1.0f);
    // Creates a fixture from a shape and attach it to this body. This is a convenience function.
    // Use b2FixtureDef if you need to set parameters like friction, restitution, user data, or
    // filtering. If the density is non-zero, this function automatically updates the mass of the body.
    /*
    b2Fixture* temp = NULL;
    for (b2Fixture* fix = playerBody->GetFixtureList(); fix; fix=fix->GetNext()) {
        std::cout << fix->GetFriction() << std::endl;
        if (fix->GetFriction() == 0.2f)
            temp = fix;
        // 여기서 바로 playerBody->DestroyFixture()를 호출하면 fix가 파괴되어 GetNext()를 호출 할 수
        // 없게 된다. 임시 변수에 저장하고 for문을 벗어나면 파괴하자.
    }
    if (temp != NULL)
        playerBody->DestroyFixture(temp);
    // 이 예제에서는 Friction값을 비교해서 삭제할 Fixture를 선택했지만 필요하다면
    // UserData를 설정해서 비교하자.
    */
 
    // 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);
 
    // 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);
 
    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);
 
        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);
 
        // 가장 마지막에 DebugDraw 그리기
        world.DebugDraw();
 
        SDL_RenderPresent(renderer);
    }
 
    delete debugDrawer;
 
    SDL_DestroyTexture(texture);
    SDL_FreeSurface(playerSurface);
    SDL_DestroyRenderer(renderer);
    SDL_DestroyWindow(window);
    SDL_Quit();
 
    return 0;
}

 

코드를 입력하고 빌드한다.

 

실행하면 공룡의 뿔같은 충돌 감지기가 추가된 모습이 보인다.

 

뿔 처럼 생긴 충돌 감지기는 크기, 위치, Density만 설정되어있다.