Function interpolate

d3-3.2.8/d3.js:2950–2959

(from, to, direction, listener)

        return (b[0] - a[0]) * (c[1] - a[1]) - (c[0] - a[0]) * (b[1] - a[1]);
      }
      function interpolate(from, to, direction, listener) {
        var a = 0, a1 = 0;
        if (from == null || (a = corner(from, direction)) !== (a1 = corner(to, direction)) || comparePoints(from, to) < 0 ^ direction > 0) {
          do {
            listener.point(a === 0 || a === 3 ? x0 : x1, a > 1 ? y1 : y0);
          } while ((a = (a + direction + 4) % 4) !== a1);
        } else {
          listener.point(to[0], to[1]);
        }
      }
      function visible(x, y) {
        return x0 <= x && x <= x1 && y0 <= y && y <= y1;
      }