clipLine method

bool clipLine(Vector4 s1, Vector4 s2)

Implementation

bool clipLine(Vector4 s1, Vector4 s2) {
  double alpha1 = 0;
  double alpha2 = 1; // Calculate the boundary coordinate of each vertex for the near and far clip planes,
  // Z = -1 and Z = +1, respectively.

  num bc1near = s1.z + s1.w, bc2near = s2.z + s2.w, bc1far = -s1.z + s1.w, bc2far = -s2.z + s2.w;

  if (bc1near >= 0 && bc2near >= 0 && bc1far >= 0 && bc2far >= 0) {
    // Both vertices lie entirely within all clip planes.
    return true;
  } else if (bc1near < 0 && bc2near < 0 || bc1far < 0 && bc2far < 0) {
    // Both vertices lie entirely outside one of the clip planes.
    return false;
  } else {
    // The line segment spans at least one clip plane.
    if (bc1near < 0) {
      // v1 lies outside the near plane, v2 inside
      alpha1 = Math.max(alpha1, bc1near / (bc1near - bc2near));
    } else if (bc2near < 0) {
      // v2 lies outside the near plane, v1 inside
      alpha2 = Math.min(alpha2, bc1near / (bc1near - bc2near));
    }

    if (bc1far < 0) {
      // v1 lies outside the far plane, v2 inside
      alpha1 = Math.max(alpha1, bc1far / (bc1far - bc2far));
    } else if (bc2far < 0) {
      // v2 lies outside the far plane, v2 inside
      alpha2 = Math.min(alpha2, bc1far / (bc1far - bc2far));
    }

    if (alpha2 < alpha1) {
      // The line segment spans two boundaries, but is outside both of them.
      // (This can't happen when we're only clipping against just near/far but good
      //  to leave the check here for future usage if other clip planes are added.)
      return false;
    } else {
      // Update the s1 and s2 vertices to match the clipped line segment.
      s1.lerp(s2, alpha1);
      s2.lerp(s1, 1 - alpha2);
      return true;
    }
  }
}