treedrawer in C++ and SDL

//Implemented by http://www.youtube.com/user/thecplusplusguy
//SDL library used
//draw a tree, at treedrawer function there are 2 commented out lines, uncomment those, to see the process
#include <iostream>
#include <SDL/SDL.h>
#include <cmath>
#include <fstream>
using namespace std;

const int BPP=32;
const int NUM=6;
const int ANGLE=70;
const int WIDTH=1024;
const int HEIGHT=768;



struct bmpfile_magic {
  unsigned char magic[2];
};

struct bmpfile_header {
  int filesz;
  short creator1;
  short creator2;
  int bmp_offset;
};

typedef struct {
  int header_sz;
  int width;
  int height;
  short nplanes;
  short bitspp;
  int compress_type;
  int bmp_bytesz;
  int hres;
  int vres;
  int ncolors;
  int nimpcolors;
} BITMAPINFOHEADER;



void saveBMP(SDL_Surface* surf)
{
    char filename[30];
    sprintf(filename,"%d.bmp",(int)time(0));
    std::ofstream out(filename,std::ios::binary);
    bmpfile_magic bm={'B','M'};
    bmpfile_header bh={54+((BPP*surf->w)/8)*surf->h,0,0,54};
    BITMAPINFOHEADER bhi={40,surf->w,surf->h,1,BPP,0,((BPP*surf->w)/8)*surf->h,2750,2750,0,0};
    out.write((char*)&bm,sizeof(bm));
    out.write((char*)&bh,sizeof(bh));
    out.write((char*)&bhi,sizeof(bhi));
    for(int i=0;i<surf->h;i++)
        for(int j=0;j<surf->w;j++)
        {
        //  std::cout << i << " " << j << std::endl;
            Uint32 rgb=(char)((Uint32*)surf->pixels)[(surf->h-i-1)*(surf->pitch/4) + j];
            Uint8 r,g,b;
            SDL_GetRGB(rgb,surf->format,&r,&g,&b);
                out.put((char)r);
                out.put((char)g);
                out.put((char)b);
                out.put((char)r);
        }
}





void putpixel(int x,int y,int r,int g,int b,int size)
{
    Uint32* pixels=(Uint32*)SDL_GetVideoSurface()->pixels;
    Uint32* pixel;
    if(size<=1)
    {
        pixel=pixels+y*SDL_GetVideoSurface()->pitch/4+x;
        *pixel=SDL_MapRGB(SDL_GetVideoSurface()->format,r,g,b);
    }else{
        for(int i=y-size/2;i<y+size/2;i++)
            for(int j=x-size/2;j<x+size/2;j++)
            {
                if(i<0 || i>=HEIGHT || j<0 || j>=WIDTH)
                    continue;
                pixel=pixels+i*SDL_GetVideoSurface()->pitch/4+j;
                *pixel=SDL_MapRGB(SDL_GetVideoSurface()->format,r,g,b);
            }
    }

}

void putpixel(int x,int y,Uint32 color,int size)
{
    Uint32* pixels=(Uint32*)SDL_GetVideoSurface()->pixels;
    Uint32* pixel;
    if(size<=1)
    {
        pixel=pixels+y*SDL_GetVideoSurface()->pitch/4+x;
        *pixel=color;
    }else{
        for(int i=y-size/2;i<ceil(y+size/2);i++)
            for(int j=x-size/2;j<ceil(x+size/2);j++)
            {
                if(i<0 || i>=HEIGHT || j<0 || j>=WIDTH)
                    continue;
                pixel=pixels+i*SDL_GetVideoSurface()->pitch/4+j;
                *pixel=color;
            }
    }
}


void csere(int& a,int &b)
{
    int tmp=a;
    a=b;
    b=tmp;
}
void drawLine(int startx,int starty,int endx,int endy,int size)
{
    bool b=abs(endy-starty)>abs(endx-startx);
    if(b)
    {
        csere(startx,starty);
        csere(endx,endy);
    }
    if(startx>endx)
    {
        csere(startx,endx);
        csere(starty,endy);
    }
    float step=abs((float)(endy-starty))/(endx-startx);
    int forstep=(endx>startx ? 1 : -1);
    float y=0;
    int ycoord=starty;
    int ystep2=(starty>endy) ? 1 : -1;
    for(int i=startx;i!=endx;i+=forstep)
    {
        if(!b)
            putpixel(i,(int)ycoord,255,255,255,size);
        else
            putpixel((int)ycoord,i,255,255,255,size);

        y+=step;
        if(y>0.5)
        {
            ycoord+=ystep2;
            y-=1.0;
        }
    }
}

void line2(int x0,int y0,int x1,int y1,int size)
{
     bool steep = abs(y1 - y0) > abs(x1 - x0);
     if(steep)
     {
         csere(x0, y0);
         csere(x1, y1);
         }

     if(x0 > x1)
     {
         csere(x0, x1);
         csere(y0, y1);
         }

     int deltax = x1 - x0;
     int deltay = abs(y1 - y0);
     float error = 0;
     float deltaerr = (float)deltay / deltax;
     int ystep;
     int y = y0;
     if(y0 < y1)
        ystep = 1;
     else
      ystep = -1;
     for(int x=x0;x<x1;x++)
     {
         if(steep)
            putpixel(y,x,255,255,255,size);
         else
          putpixel(x,y,255,255,255,size);
         error = error + deltaerr;
         if(error>= 0.5)
         {
             y = y + ystep;
             error = error - 1.0;
         }
     }
}

void drawTree(int startx,int starty,int len,int vast,float dir)
{
    if(vast>=1)
    {
        float endx=startx+sin((float)dir*M_PI/180.0)*len;
        float endy=starty+cos((float)dir*M_PI/180.0)*len;
        line2(startx,starty,endx,endy,vast);
        //comment out for immediate result
        //SDL_Flip(SDL_GetVideoSurface());
        //SDL_Delay(1);
        for(int j=-ANGLE;j<=ANGLE;j+=(ANGLE*2)/(NUM-1))
            drawTree(endx,endy,len/2,vast-1,dir+j);
    }
}




int main()
{
    srand(time(0));
    SDL_Init(SDL_INIT_EVERYTHING);
    SDL_Surface* screen=SDL_SetVideoMode(WIDTH,HEIGHT,BPP,SDL_SWSURFACE);
    bool running=true;
    SDL_Event event;
    Uint32 start;
    int i=0;
    int j=0;
    bool dir=true;
    while(running)
    {
        start=SDL_GetTicks();
        while(SDL_PollEvent(&event))
        {
            switch(event.type)
            {
                case SDL_QUIT:
                    running=false;
                    break;
            }
        }
        SDL_FillRect(screen,&screen->clip_rect,SDL_MapRGB(screen->format,0,0,0));
        drawTree(WIDTH/2,HEIGHT,HEIGHT/2,6,180);
    //  cout << "-----------------------------------" << endl;
        SDL_Flip(screen);


        saveBMP(screen);



    //  SDL_Delay(2000);
        break;
        if(1000.0/30>(SDL_GetTicks()-start))
            SDL_Delay(1000.0/30-(SDL_GetTicks()-start));
    }

    SDL_Quit();
}