are global constants. OutCode ComputeOutCode(double x, double y) { OutCode code = INSIDE; // initialised as being inside of clip window if (x < xmin) // to the left of clip window code |= LEFT; else if (x > xmax) // to the right of clip window code |= RIGHT; if (y < ymin) // below the clip window code |= BOTTOM; else if (y > ymax) // above the clip window code |= TOP; return code; } // Cohen–Sutherland clipping algorithm clips a line from // P0 = (x0, y0) to P1 = (x1, y1) against a rectangle with // diagonal from (xmin, ymin) to (xmax, ymax). bool CohenSutherlandLineClip(double& x0, double& y0, double& x1, double& y1) { // compute outcodes for P0, P1, and whatever point lies outside the clip rectangle OutCode outcode0 = ComputeOutCode(x0, y0); OutCode outcode1 = ComputeOutCode(x1, y1); bool accept = false; while (true) { if (!(outcode0 | outcode1)) { // bitwise OR is 0: both points inside window; trivially accept and exit loop accept = true; break; } else if (outcode0 & outcode1) { // bitwise AND is not 0: both points share an outside zone (LEFT, RIGHT, TOP, // or BOTTOM), so both must be outside window; exit loop (accept is false) break; } else { // failed both tests, so calculate the line segment to clip // from an outside point to an intersection with clip edge double x, y; // At least one endpoint is outside the clip rectangle; pick it. OutCode outcodeOut = outcode1 > outcode0 ? outcode1 : outcode0; // Now find the intersection point; // use formulas: // slope = (y1 - y0) / (x1 - x0) // x = x0 + (1 / slope) * (ym - y0), where ym is ymin or ymax // y = y0 + slope * (xm - x0), where xm is xmin or xmax // No need to worry about divide-by-zero because, in each case, the // outcode bit being tested guarantees the denominator is non-zero if (outcodeOut & TOP) { // point is above the clip window x = x0 + (x1 - x0) * (ymax - y0) / (y1 - y0); y = ymax; } else if (outcodeOut & BOTTOM) { // point is below the clip window x = x0 + (x1 - x0) * (ymin - y0) / (y1 - y0); y = ymin; } else if (outcodeOut