仮定が多すぎるナ。まあ、一番素直な方法で。苦情は受け付けません(w

#include <windows.h>
int main(){
int x,y, mx=320, my=240;
double a,b,c,d,e,f;
HDC dc = GetDC(NULL);
scanf("%lf %lf %lf %lf %lf %lf",
&a, &b, &c, &d, &e, &f);
for( y=-my; y<my; y++)
for( x=-mx; x<mx; x++ )
if( a*x + b*y + c > 0 &&
d*x + e*y + f > 0 )
SetPixelV(dc, x+mx, y+my, RGB(255,255,255));
else
SetPixelV(dc, x+mx, y+my, 0);
SetPixelV(dc, mx, my, RGB(0,0,255));
ReleaseDC(NULL,dc);
}