#include <allegro.h>
#define red makecol(255,0,0)
#define green makecol(0,255,0)

double xmax,xmin,ymax,ymin;

float max(float value1, float value2)
{
return ( (value1 > value2) ? value1 : value2);
}
float min(float value1, float value2)
{
return ( (value1 < value2) ? value1 : value2);
}

int LiangBarsky(double xw0, double yw0, double xw1, double yw1, int colour, bool bscreen, BITMAP * buf, BITMAP * buffer)
{
        double x1,y1,x2,y2;
        double xwmin,ywmin,xwmax,ywmax;

        x1 = xw0;
        y1 = yw0;
        x2 = xw1;
        y2 = yw1;
        xwmin = xmin;
        xwmax = xmax;
        ywmin = ymin;
        ywmax = ymax;
        /*printf("enter the endpoints of the line");
        scanf("%d %d %d %d",&x1,&y1,&x2,&y2);
        printf("\nEnter the corners of the window");
        scanf("\n%d %d %d %d",&xwmin,&ywmin,&xwmax,&ywmax);
        */
        int p[5],q[5];
        p[1]=-(x2-x1);
        p[2]=x2-x1;
        p[3]=-(y2-y1);
        p[4]=y2-y1;
        q[1]=x1-xwmin;
        q[2]=xwmax-x1;
        q[3]=y1-ywmin;
        q[4]=ywmax-y1;
        int i;
        for(i=1;i<5;i++)
        {
                if(p[i]==0)
                {
                        //linia jest rownolegla
                        if (q[i]<0)
                        {
                                //Linia jest poza obszarem, rysujemy tylko kwadrat
                                rect(buf,xwmin,ywmin,xwmax,ywmax,red);
                                return(0);
                        }
                }
        }
        float u1=0,u2=1;
        float r[5];
        for(i=1;i<5;i++)
        { if(p[i]!=0)
        r[i]=q[i]*1.0/p[i];
        }

        for(i=1;i<5;i++)
        {
                if(p[i]==0)
                        continue;
                if(p[i]<0)
                {
                        u1=max(u1, r[i]);
                }
                else
                { u2=min(u2, r[i]);
                }
        }
        rect(buf,xwmin,ywmin,xwmax,ywmax,red);
        //wyliczamy wspolrzedne nowych punktow linii
        if(u1<u2)
        {
        int xx1=x1+u1*(x2-x1);
        int yy1=y1+u1*(y2-y1);
        int xx2=x1+u2*(x2-x1);
        int yy2=y1+u2*(y2-y1);

        if(bscreen) //jezeli mamy rysowac na ekranie
        {
                rect(buf,xmin,ymin,xmax,ymax, colour);
                line(buf,xx1,yy1,xx2,yy2,red);
        }
        else //jezeli mamy rysowac na obszarze powiekszenia
        {
                rect(buffer,0,0,200,200, red);
                line(buffer,2*(x1-xmin),2*(y1-ymin),2*(x2-xmin),2*(y2-ymin),red);
                blit(buffer,buf,0,0,600,0,200,201);
        }
        }
}

int main(){

    allegro_init();
    install_keyboard();
    set_gfx_mode( GFX_AUTODETECT_WINDOWED, 800, 600, 0, 0);
        clear_to_color(screen,makecol(0,0,0));
        BITMAP *buf;
        buf = create_bitmap(800, 600);
        BITMAP *buffer;
        buffer = create_bitmap(200, 201);
        clear_to_color(buffer, makecol(0,0,0));

        //ustawienie rozmiarow kwadratu
        xmax = 200;
        ymax = 200;
        xmin = 100;
        ymin = 100;
        while(!key[KEY_ESC])
        {
                clear_to_color(buf,makecol(0,0,0));
                clear_to_color(buffer,makecol(0,0,0));
                //rysuje linie na ekranie(buf) -> rysunek oryginalny
                for (int i=200; i<600;i+=100)
                {
                line(buf,0,0,i,i+100,green);
                }

                if(key[KEY_W])
                {
                        ymax--;
                        ymin--;
                }
                if(key[KEY_S])
                {
                        ymax++;
                        ymin++;
                }
                if(key[KEY_A])
                {
                        xmax--;
                        xmin--;
                }
                if(key[KEY_D])
                {
                        xmax++;
                        xmin++;
                }
                //dla wyrysowanych linii wykonuje rysunki obcietego kwadratu na ekranie bscreen=true i buforze bscreen=false, buffer to powiekszony obciety kwadrat
                for (int i=200; i<600;i+=100)
                {
                        LiangBarsky(0,0,i,i+100,red,true,buf,buffer);
                        LiangBarsky(0,0,i,i+100,red,false,buf,buffer);
                }

                blit(buf,screen,0,0,0,0,800,600);
        }
    return 0;

}
END_OF_MAIN();