circle collision example

//http://www.youtube.com/user/thecplusplusguy
//you need cirlce.bmp 20x20 bmp image containing a 10 pixel radius (20 diameter) circle
//circle collision example
#include <SDL/SDL.h>
#include <iostream>

struct Circle
{
    SDL_Rect position;
    SDL_Surface* image;
    int radius;
    Circle(SDL_Surface* img, int x,int y,int radius)
    {
        image=img;
        position.x=x;
        position.y=y;
        this->radius=radius;
    }

    void render()
    {
        SDL_BlitSurface(image,NULL,SDL_GetVideoSurface(),&position);
    }

    bool intersects(Circle* c)
    {
        int x=c->position.x - position.x;
        int y=c->position.y - position.y;
        int r=radius + c->radius;
        return (x*x + y*y < r*r);   //a^2+b^2=c^2
    }

    bool intersects(SDL_Rect* rec)
    {
        //source: http://stackoverflow.com/questions/401847/circle-rectangle-collision-detection-intersection
    int circleDistanceX = abs(position.x - rec->x);
    int circleDistanceY = abs(position.y - rec->y);

    if (circleDistanceX > (rec->w/2 + radius)) { return false; }
    if (circleDistanceY > (rec->h/2 + radius)) { return false; }

    if (circleDistanceX <= (rec->w/2)) { return true; }
    if (circleDistanceY <= (rec->h/2)) { return true; }

    int cornerDistance_sq = ((float)circleDistanceX - rec->w/2)*(circleDistanceX - rec->w/2) + (circleDistanceY - rec->h/2)*(circleDistanceY - rec->h/2);

    return (cornerDistance_sq <= (radius*radius));
    }
};

int main(int argc, char** argv)
{
    SDL_Init(SDL_INIT_EVERYTHING);
    SDL_Surface* screen = SDL_SetVideoMode(640, 480, 32, SDL_SWSURFACE);
    bool running = true;
    const int FPS = 30;
    Uint32 start;
    bool b[4] = {0,0,0,0};
    SDL_Rect rect;
    rect.x = 10;
    rect.y = 10;
    rect.w = 20;
    rect.h = 20;
    SDL_Surface* circle=SDL_LoadBMP("circle.bmp");
    if(!circle)
    {
        std::cout << "You need circle.bmp" << std::endl;
        return 1;
    }
    Circle circle1(circle,30,30,10);
    Circle circle2(circle,50,50,10);
    SDL_SetColorKey(circle,SDL_SRCCOLORKEY,SDL_MapRGB(screen->format,255,0,255));
    while(running) {
        start = SDL_GetTicks();
        SDL_Event event;
        while(SDL_PollEvent(&event)) {
            switch(event.type) {
                case SDL_QUIT:
                    running = false;
                    break;
                case SDL_KEYDOWN:
                    switch(event.key.keysym.sym) {
                        case SDLK_UP:
                            b[0] = 1;
                            break;
                        case SDLK_LEFT:
                            b[1] = 1;
                            break;
                        case SDLK_DOWN:
                            b[2] = 1;
                            break;
                        case SDLK_RIGHT:
                            b[3] = 1;
                            break;

                    }
                    break;
                case SDL_KEYUP:
                    switch(event.key.keysym.sym) {
                        case SDLK_UP:
                            b[0] = 0;
                            break;
                        case SDLK_LEFT:
                            b[1] = 0;
                            break;
                        case SDLK_DOWN:
                            b[2] = 0;
                            break;
                        case SDLK_RIGHT:
                            b[3] = 0;
                            break;

                    }
                    break;
            }
        }

        //logic
        if(b[0])
            rect.y--;
        if(b[1])
            rect.x--;
        if(b[2])
            rect.y++;
        if(b[3])
            rect.x++;
        unsigned char* downKeys=SDL_GetKeyState(0);
        if(downKeys[SDLK_w])
            circle1.position.y--;
        if(downKeys[SDLK_s])
            circle1.position.y++;
        if(downKeys[SDLK_a])
            circle1.position.x--;
        if(downKeys[SDLK_d])
            circle1.position.x++;

        if(downKeys[SDLK_u])
            circle2.position.y--;
        if(downKeys[SDLK_j])
            circle2.position.y++;
        if(downKeys[SDLK_h])
            circle2.position.x--;
        if(downKeys[SDLK_k])
            circle2.position.x++;


        SDL_FillRect(screen,0,0);   //clear screen
        SDL_FillRect(screen, &rect, SDL_MapRGB(screen->format,255,0,0));    // fill the screen white (maybe better outside while loop)

        circle1.render();
        circle2.render();

        if(circle1.intersects(&circle2))
            std::cout << "Two cirlces intersecting" << std::endl;
        if(circle1.intersects(&rect))
            std::cout << "Circle1 intersects rect" << std::endl;
        if(circle2.intersects(&rect))
            std::cout << "Circle2 intersects rect" << std::endl;

        SDL_Flip(screen);

        if(1000/FPS > SDL_GetTicks()-start) {
            SDL_Delay(1000/FPS-(SDL_GetTicks()-start));
        }
    }
    SDL_Quit();
    return 0;
}