SDL simple lighting example

//http://www.youtube.com/user/thecplusplusguy
//SDL very simple lighting model, just click, to put down a new lamp
#include <iostream>
#include <vector>
#include <SDL/SDL.h>
#include <cmath>

const int WIDTH=640;
const int HEIGHT=480;
const float lightStrength=10.0;
float light[HEIGHT][WIDTH];

void putPixel(SDL_Surface* dest,int x,int y,unsigned char r,unsigned char g,unsigned char b)
{
//  std::cout << x << " " << y << std::endl;
    if(x>=0 && x<dest->w && y>=0 && y<dest->h)
        ((Uint32*)dest->pixels)[y*dest->pitch/4+x]=SDL_MapRGB(dest->format,r,g,b);
}

void getPixel(SDL_Surface* img,int x,int y,unsigned char& r,unsigned char& g,unsigned char& b)
{
    if(x>=0 && x<img->w && y>=0 && y<img->h)
    {
        Uint32 pix=((Uint32*)img->pixels)[y*img->pitch/4+x];
        SDL_GetRGB(pix,img->format,&r,&g,&b);
    }
}

void blitImage(SDL_Surface* srcImage,SDL_Rect* srcRect,SDL_Surface* dstScreen,SDL_Rect* dstRect)
{
    int sx,sy,sw,sh;
    int dx,dy;
    if(srcRect==NULL)
    {
        sx=0;
        sy=0;
        sw=srcImage->w;
        sh=srcImage->h;
    }else{
        sx=srcRect->x;
        sy=srcRect->y;
        sw=srcRect->w;
        sh=srcRect->h;
    }
    if(dstRect==NULL)
    {
        dx=0;
        dy=0;
    }else{
        dx=dstRect->x;
        dy=dstRect->y;
    }
    unsigned char r,g,b;
    for(int i=sy;i<sh;i++)
        for(int j=sx;j<sw;j++)
        {
            getPixel(srcImage,j,i,r,g,b);
            r*=light[i][j];
            g*=light[i][j];
            b*=light[i][j];
            putPixel(dstScreen,dx+j,dy+i,r,g,b);
        }
}

int main(int argc,char** argv)
{
    SDL_Init(SDL_INIT_EVERYTHING);
    SDL_Surface* screen=SDL_SetVideoMode(640,480,32,SDL_SWSURFACE);
    bool running=true;
    SDL_Event event;
    Uint32 start;
    int mx=10,my=10;
    SDL_Surface* image=SDL_LoadBMP("test.bmp");
    SDL_Surface* optImage=SDL_DisplayFormat(image);
    SDL_FreeSurface(image);
    for(int i=0;i<HEIGHT;i++)
        for(int j=0;j<WIDTH;j++)
            light[i][j]=0.05;
    std::vector<SDL_Rect> lightSources;
    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;
                    }
                    break;
                case SDL_MOUSEMOTION:
                    mx=event.motion.x;
                    my=event.motion.y;
                    break;
                case SDL_MOUSEBUTTONDOWN:
                {
                    SDL_Rect rec;
                    rec.x=event.button.x;
                    rec.y=event.button.y;
                    lightSources.push_back(rec);
                    for(int i=0;i<HEIGHT;i++)
                        for(int j=0;j<WIDTH;j++)
                        {
                            light[i][j]=0.05;   //ambient
                            for(int k=0;k<lightSources.size();k++)
                            {
                                //(vector length squared)*lightStrength
                                float dstSquared=(lightSources[k].x-j)*(lightSources[k].x-j) + (lightSources[k].y-i)*(lightSources[k].y-i);
                                if(dstSquared!=0.0)
                                {
                                    light[i][j]+=(lightStrength/(0.01*dstSquared)); //put some nice functions here
                                    //light[i][j]+=lightStrength/sqrt(dstSquared);
                                }else
                                    light[i][j]=1.0;
                                if(light[i][j]>1.0)
                                    light[i][j]=1.0;
                            }
                        }

                }
            }
        }
        SDL_FillRect(screen,NULL,0);
        blitImage(optImage,0,screen,0);
        SDL_Flip(screen);
        if(1000.0/30>(SDL_GetTicks()-start))
            SDL_Delay(1000.0/30-(SDL_GetTicks()-start));
    }
    SDL_FreeSurface(optImage);
    SDL_Quit();
}