Cool rain effect C++, SDL

//Implemented by http://www.youtube.com/user/thecplusplusguy
//The algorithm: http://freespace.virgin.net/hugo.elias/graphics/x_water.htm
//SDL library used
//You need a 640x480 image (more colorful the better), called waterback.bmp in the same folder
#include <iostream>
#include <SDL/SDL.h>
using namespace std;

const int WIDTH=640;
const int HEIGHT=480;
const int FPS=60;
int dumpv2=8;
int WATERHIGHT=200;
const float dump=0.99;
int** buffer1;
int** buffer2;


void putPixel(SDL_Surface* surf,int x,int y,int r,int g,int b)
{
    if(x>=0 && y>=0 && x<WIDTH && y<HEIGHT)
    {
        (((Uint32*)(surf->pixels))[y*surf->pitch/4 + x])=SDL_MapRGB(surf->format,r,g,b);
    }
}

void putPixel(SDL_Surface* surf,int x,int y,Uint32 col)
{
    if(x>=0 && y>=0 && x<WIDTH && y<HEIGHT)
    {
        ((Uint32*)(surf->pixels))[y*surf->pitch/4 + x]=col;
    }
}

Uint32 getPixel(SDL_Surface* surf,int x,int y)
{
    if(x<0)
        x=0;
    if(y<0)
        y=0;
    if(x>=WIDTH)
        x=WIDTH-1;
    if(y>=HEIGHT)
        y=HEIGHT-1;
    return (((Uint32*)(surf->pixels))[y*surf->pitch/4 + x]);
}

void refreshWater()
{
    for(int i=1;i<HEIGHT-1;i++)
        for(int j=1;j<WIDTH-1;j++)
        {
            buffer2[i][j]=((buffer1[i][j-1]+buffer1[i][j+1]+buffer1[i-1][j]+buffer1[i+1][j]) >> 1) - buffer2[i][j];
    //      buffer2[i][j]*=dump;
            buffer2[i][j]-=buffer2[i][j]>>dumpv2;
        }
    int **tmp;
    tmp=buffer2;
    buffer2=buffer1;
    buffer1=tmp;
}

void renderWater(SDL_Surface* screen,SDL_Surface* backImg)
{
    for(int i=1;i<HEIGHT-1;i++)
        for(int j=1;j<WIDTH-1;j++)
        {
            int diffY=buffer1[i-1][j]-buffer1[i+1][j];
            int diffX=buffer1[i][j-1]-buffer1[i][j+1];
    //      cout << diffX << " " << diffY << endl;
            putPixel(screen,j,i,getPixel(screen,j+diffY,i+diffX));
        }
}


int main(int argc,char** argv)
{
    buffer1=(int**)new int[HEIGHT];
    buffer2=(int**)new int[HEIGHT];
    for(int i=0;i<HEIGHT;i++)
    {
        buffer1[i]=new int[WIDTH];
        buffer2[i]=new int[WIDTH];
    }
    for(int i=0;i<HEIGHT;i++)
        for(int j=0;j<WIDTH;j++)
            buffer1[i][j]=buffer2[i][j]=0;
    SDL_Init(SDL_INIT_EVERYTHING);
    SDL_Surface* screen=SDL_SetVideoMode(WIDTH,HEIGHT,32,SDL_SWSURFACE);
    SDL_Surface* backImgTmp=SDL_LoadBMP("waterback.bmp");
    SDL_Surface* backImg=SDL_DisplayFormat(backImgTmp);
    if(!backImg)
        cout << "error with the image" << endl;
    SDL_FreeSurface(backImgTmp);
    SDL_Event event;
    bool running=true;
    Uint32 start;
    int x,y;
    int num=10;
    while(running)
    {
        start=SDL_GetTicks();
        while(SDL_PollEvent(&event))
        {
            switch(event.type)
            {
                case SDL_QUIT:
                    running=false;
                    break;
                case SDL_KEYDOWN:
                    switch(event.key.keysym.sym)
                    {
                        case SDLK_ESCAPE:
                            running=false;
                            break;
                        case SDLK_q:
                            num++;
                            break;
                        case SDLK_a:
                            if(num>0)
                                num--;
                            break;
                        case SDLK_w:
                            WATERHIGHT+=20;
                            break;
                        case SDLK_s:
                            if(WATERHIGHT>20)
                                WATERHIGHT-=20;
                            break;
                    }
                    break;
            }
        }
        //if(rand()%10<8)
        for(int i=0;i<num;i++)
            buffer1[rand()%HEIGHT][rand()%WIDTH]+=rand()%WATERHIGHT+1;
        SDL_BlitSurface(backImg,NULL,screen,NULL);
        refreshWater();
        renderWater(screen,backImg);

        SDL_Flip(screen);
        if(1000.0/FPS>(SDL_GetTicks()-start))
            SDL_Delay(1000.0/FPS-(SDL_GetTicks()-start));
    }
    for(int i=0;i<HEIGHT;i++)
    {
        delete[] buffer1[i];
        delete[] buffer2[i];
    }
    delete[] buffer1;
    delete[] buffer2;
    SDL_FreeSurface(backImg);
    SDL_Quit();
}