Function ClipEdge

renderer/HardwareClipper.cpp:179–254

clips an edge against one plane.

// clips an edge against one plane.
g3Point *ClipEdge(int plane_flag, g3Point *on_pnt, g3Point *off_pnt) {
  float a, b, k;
  g3Point *tmp;

  // compute clipping value k = (xs-zs) / (xs-xe-zs+ze)
  // use x or y as appropriate, and negate x/y value as appropriate

  if (plane_flag & CC_OFF_FAR) {
    return ClipFarEdge(on_pnt, off_pnt);
  }

  if ((plane_flag & CC_OFF_CUSTOM) && Clip_custom) {
    return ClipCustomEdge(on_pnt, off_pnt);
  }

  if (plane_flag & (CC_OFF_RIGHT | CC_OFF_LEFT)) {
    a = on_pnt->p3_x;
    b = off_pnt->p3_x;
  } else {
    a = on_pnt->p3_y;
    b = off_pnt->p3_y;
  }

  if (plane_flag & (CC_OFF_LEFT | CC_OFF_BOT)) {
    a = -a;
    b = -b;
  }

  k = (a - on_pnt->p3_z) / ((a - on_pnt->p3_z) - b + off_pnt->p3_z); //(xs-zs) / (xs-zs-xe+ze)

  tmp = GetTempPoint();

  tmp->p3_x = on_pnt->p3_x + ((off_pnt->p3_x - on_pnt->p3_x) * k);
  tmp->p3_y = on_pnt->p3_y + ((off_pnt->p3_y - on_pnt->p3_y) * k);

  if (plane_flag & (CC_OFF_TOP | CC_OFF_BOT)) {
    tmp->p3_z = tmp->p3_y;
  } else {
    tmp->p3_z = tmp->p3_x;
  }

  if (plane_flag & (CC_OFF_LEFT | CC_OFF_BOT)) {
    tmp->p3_z = -tmp->p3_z;
  }

  if (on_pnt->p3_flags & PF_UV) {
    tmp->p3_u = on_pnt->p3_u + ((off_pnt->p3_u - on_pnt->p3_u) * k);
    tmp->p3_v = on_pnt->p3_v + ((off_pnt->p3_v - on_pnt->p3_v) * k);

    tmp->p3_flags |= PF_UV;
  }

  if (on_pnt->p3_flags & PF_UV2) {
    tmp->p3_u2 = on_pnt->p3_u2 + ((off_pnt->p3_u2 - on_pnt->p3_u2) * k);
    tmp->p3_v2 = on_pnt->p3_v2 + ((off_pnt->p3_v2 - on_pnt->p3_v2) * k);

    tmp->p3_flags |= PF_UV2;
  }