import Vertex2D;

// taken from lecture notes
class EdgeEqn {
          public final static int FRACBITS = 12;
          public int A, B, C;
          public int flag;            // used to compute bounding box
          
          public EdgeEqn(Vertex2D v0, Vertex2D v1) {
              double a = v0.y - v1.y;
              double b = v1.x - v0.x;
              double c = -0.5f*(a*(v0.x + v1.x) + b*(v0.y + v1.y));
              A = (int) (a * (1<<FRACBITS));
              B = (int) (b * (1<<FRACBITS));
              C = (int) (c * (1<<FRACBITS));
              flag = 0;
              if (A >= 0) flag += 8;
              if (B >= 0) flag += 1;
          }

          public void flip() {
              A = -A;
              B = -B;
              C = -C;
          }
          
          public int evaluate(int x, int y) {
              return (A*x + B*y + C);
          }
      }