/* Kääntäminen: gcc -o metaballs metaballs.c -O3 -ggdb -lSDL -lm */

#include <stdlib.h>
#include <math.h>
#include <SDL/SDL.h>

#define RES_X 800
#define RES_Y 800

typedef struct metaball {
    int x, y;
    unsigned char r, g, b;
    float vx, vy;
    float fx, fy;
    float mass;
} metaball;

typedef union {
    struct {unsigned char b, g, r;} rgb;
    Uint32 sdl;
} unioncolor;

metaball pallot[3] = {
    {0,0,255,0,0,0.0,-8.0,100.0,400.0,5.0},
    {0,0,0,255,0,0.0,8.0,600.0,400.0,1.0},
    
    {400,400,0,0,255,0,0,400.0,400.0,400.0}
};

const int pallot_count = 3;

inline Uint32 rgb(int r, int g, int b){
    return (r << 16) | (g << 8) | b;
}

inline void putpixel(SDL_Surface *screen, int x, int y, Uint32 color){
        Uint8 *p = (Uint8 *)screen->pixels;
        *(Uint32 *)(p + y * screen->pitch + (x << 2)) = color;
}

void draw(SDL_Surface *screen)
{
    int i, x, y, dx, dy;
    long factor;
    long total;
    long r, g, b;
    unioncolor *pixel;
    
    for (x=0; x<RES_X; x++) {
        for (y=0; y<RES_Y; y++) {
            r = g = b = 0;
            total = 0;
            
            for (i=0; i<pallot_count; i++) {
                dx = pallot[i].x - x;
                dy = pallot[i].y - y;

                if (dx == 0 && dy == 0)
                    factor = pallot[i].mass * 50000;
                else
                    factor = pallot[i].mass * 50000 / (dx * dx + dy * dy);

                if (factor > 10000)
                    factor = 10000;
                
                if (factor < 10)
                    continue;
                
                r += (pallot[i].r * factor) >> 10;
                g += (pallot[i].g * factor) >> 10;
                b += (pallot[i].b * factor) >> 10;
                
                total += factor;
            }

//             if (total > 5000 && total < 5500)
//                 total = 0;
            
            r = (total * r) >> 10;
            g = (total * g) >> 10;
            b = (total * b) >> 10;

            if (r > 255)
                r = 255;
            if (g > 255)
                g = 255;
            if (b > 255)
                b = 255;

            pixel = (Uint8 *)screen->pixels + y * screen->pitch + (x << 2);
            pixel->rgb.r = r;
            pixel->rgb.g = g; 
            pixel->rgb.b = b;
        }
    }

    SDL_Flip(screen);
}

void reposition() {
    int i, j;
    float fx, fy, ft;
    int dx, dy;
    float fdist, vx, vy;

    for (i=0; i<pallot_count; i++) {
        fx = fy = 0.0;
        
        for (j=0; j<pallot_count; j++) {
            if (j == i)
                continue;

            vx = dx = pallot[j].x - pallot[i].x;
            vy = dy = pallot[j].y - pallot[i].y;

            if (dx == 0 && dy == 0)
                continue;

            fdist = dx * dx + dy * dy;
            
//             if (fdist < 10000.0)
//                 continue;
            
            ft = sqrt(fdist);
            
            vx /= ft;
            vy /= ft;
            
            ft = (pallot[j].mass * pallot[i].mass) / fdist;

            fx += 50.0 * vx * ft;
            fy += 50.0 * vy * ft;
        }

        pallot[i].vx += fx / pallot[i].mass;
        pallot[i].vy += fy / pallot[i].mass;

        pallot[i].fx += pallot[i].vx;
        pallot[i].fy += pallot[i].vy;
        
        pallot[i].x = pallot[i].fx;
        pallot[i].y = pallot[i].fy;
    }
}

int main(int argc, char *argv[]) 
{ 
    if( SDL_Init(SDL_INIT_VIDEO) < 0 )
    {
        printf("Unable to init SDL: %s\n", SDL_GetError());
        exit(1);
    }
    
    atexit(SDL_Quit);
    SDL_Surface *screen;
    screen = SDL_SetVideoMode(RES_X, RES_Y, 32, SDL_HWSURFACE|SDL_DOUBLEBUF);
    
    long ticks;
    
    while(1)
    {
        ticks = SDL_GetTicks() + 40; // Vakio 25 fps
        
        SDL_Event event;
        while( SDL_PollEvent(&event) )
        {
            if( event.type == SDL_QUIT || event.type == SDL_KEYDOWN )
                exit(0);
        }

        reposition();
        draw(screen);
    
        ticks -= SDL_GetTicks();
        if (ticks > 0)
            SDL_Delay(ticks);
    }
    return 0;
}