pointVersusManifoldXZ.vfl

//Line has 2 coodinate pairs. L1:x1x2y1y2 & L2:x3,x4,y3,y4
vector segsegXZ(float x1; float y1;float x2;float y2;float x3;float y3;float x4;float y4) {
  float a1, a2, b1, b2, c1, c2; // Coefficients of line eqns.
  float r1, r2, r3, r4;         // 'Sign' values
  float denom, offset;          // Intermediate values
  float x, y;                   // Intermediate return values

  // Compute a1, b1, c1, where line joining points 1 and 2
  // is "a1 x  +  b1 y  +  c1  =  0".
  a1 = y2 - y1;
  b1 = x1 - x2;
  c1 = x2 * y1 - x1 * y2;

  // Compute r3 and r4.
  r3 = a1 * x3 + b1 * y3 + c1;
  r4 = a1 * x4 + b1 * y4 + c1;

  // Check signs of r3 and r4.  If both point 3 and point 4 lie on
  // same side of line 1, the line segments do not intersect.
  if ( r3 != 0 && r4 != 0 && ((r3 >= 0 && r4 >= 0) || (r3 < 0 && r4 < 0))) {
    return({0,-1,0});// no intersection
  }


  // Compute a2, b2, c2
  a2 = y4 - y3;
  b2 = x3 - x4;
  c2 = x4 * y3 - x3 * y4;

  // Compute r1 and r2
  r1 = a2 * x1 + b2 * y1 + c2;
  r2 = a2 * x2 + b2 * y2 + c2;

  // Check signs of r1 and r2.  If both point 1 and point 2 lie
  // on same side of second line segment, the line segments do
  // not intersect.
  if (r1 != 0 && r2 != 0 && ((r1 >= 0 && r2 >= 0) || (r1 < 0 && r2 < 0))) {
    return({0,-1,0});// no intersection
  }

  // Line segments intersect: compute intersection point.
  denom = a1 * b2 - a2 * b1;

  if ( denom == 0 ) {
    return({0,-2,0});//true.
  }

  offset = denom < 0 ? - denom / 2 : denom / 2;

  x = b1 * c2 - b2 * c1;
  y = a2 * c1 - a1 * c2;

  float retx=( x < 0 ? x : x ) / denom;
  float rety=( y < 0 ? y : y ) / denom;
  return(set(retx,0,rety));
}
void drawAngle(vector position;float scale; float radians; vector color){
  //draw a circle with 10 points.
  float pi = 3.141592;
  int circle = addprim(0,"polyline");
  float total = 5;
  for(int points=0;points<total;points++){
        float fraction = points/total;
        int p = addpoint(0, set(position[0]+cos(fraction*2*pi)*scale ,position[1],position[2]+sin(fraction*2*pi)*scale));
        int pass = setpointattrib(0, "Cd", p, color/5, "set");
        addvertex(0, circle, p);
  }
  int p = addpoint(0, set(position[0]+1*scale ,position[1],position[2]+0*scale));
  int pass = setpointattrib(0, "Cd", p, color/5, "set");
  addvertex(0, circle, p);
  //draw angle
  int direction = addprim(0,"polyline");
  int p0 = addpoint(0,position);
  int p1 = addpoint(0,set(position[0]+cos(radians)*scale ,position[1],position[2]+sin(radians)*scale));
  pass = setpointattrib(0, "Cd", p0, color*2, "set");
  pass = setpointattrib(0, "Cd", p1, color*2, "set");

  addvertex(0,direction,p0);
  addvertex(0,direction,p1);

  int reference = addprim(0,"polyline");
  int p00 = addpoint(0, set(position[0]+(1*scale),position[1],position[2]+(0*scale)));
  int p01 = addpoint(0, set(position[0]+(1.2*scale),position[1],position[2]+(0*scale)));
  pass = setpointattrib(0, "Cd", p00, color, "set");
  pass = setpointattrib(0, "Cd", p01, color, "set");
  addvertex(0,reference,p00);
  addvertex(0,reference,p01);
}

int pointCount1 = npoints(1);
int nprim2 = nprimitives(2);

for(int pnt=0;pnt<pointCount1;pnt++){ //for each point in channel 1
  int c = -1; //-1 == false.
  vector cLoc = point(1,"P",pnt);
  float cx = cLoc[0];
  float cy = cLoc[2];
  for(int collisionPrim=0;collisionPrim<nprim2;collisionPrim++){//for each primitive in channel 2
    int CollisionPoints[] = primpoints(2,collisionPrim);
    int close2 =  primintrinsic(2, "closed", collisionPrim);
    for(int primEdge=len(CollisionPoints)-1; primEdge>-close2;primEdge--){
      int pointA = CollisionPoints[primEdge];
      int pointB = CollisionPoints[primEdge-1];
      vector pointALoc = point(2,"P",pointA);
      vector pointBLoc = point(2,"P",pointB);
      float ax = pointALoc[0];
      float ay = pointALoc[2];
      float bx = pointBLoc[0];
      float by = pointBLoc[2];
      if((ay <= cy && cy < by) || (by <= cy && cy < ay)){
        if((cx < (bx - ax) * (cy - ay) / (by - ay) + ax)){
          c= c*-1;
        }
      }
    }
  }
  if(c==1){
    drawAngle(cLoc,0.04,0.0,hsvtorgb(0,1,2));
  }else{
    drawAngle(cLoc,0.03,0.0,hsvtorgb(0.333,1,1));
  }
}