void myActions() { // actions to be executed at each frame
    scribe("Jarek Rossignac's edge / tringle intersection");         //*:01 prints text at top of the graphic window (see TAB UI), line 0
    if ((mousePressed)&&(!keyPressed)) dragPoint();    // while mouse pressed moves the selected point by mouse displacement (in TAB polygon)
    fill(black);              // set fill color to black (for writing text in the windows)
    strokeWeight(3);          // set stroke width to 3
    stroke(blue);             // set current color to blue
    pt A=P[0]; A.show(2); A.showLabel("A");  // Assign variable point A to P[0], show it as a disk of radius 4, write its label "A" next to it
    pt B=P[1]; B.show(2); B.showLabel("B"); 
    pt C=P[2]; C.show(2); C.showLabel("C");  //*:03
    stroke(dgreen); fill(cyan,200); beginShape();  A.v(); B.v(); C.v(); endShape(CLOSE); //*:04 show triangle (A,B,C)
    fill(black);              //*:05 reset fill color to black (for writing text in the windows)
    pt D=P[3]; D.show(2); D.showLabel("D");
    pt E=P[4]; E.show(2); E.showLabel("E");  //*:06 a fifth point
    stroke(dblue); D.to(E);                  //*:07 show edge (D,E)
    stroke(red); strokeWeight(5); showEdgeTirangleIntersection(A,B,C,D,E);      //*:08
    stroke(orange); strokeWeight(5); showEdgeTirangleBorderIntersection(A,B,C,D,E);  //*:30
    };

void showEdgeTirangleIntersection(pt A, pt B, pt C, pt D, pt E) { //*:09 show intersection between triangle(A,B,C) and edge(D,E)
    //*:15 if (edgesCross(A, B, D, E)) show(EE(A, B, D, E));        //*:14 Debug test if edge(A,B) and edge(D,E) actually intersect (see below)
    if (D.isInTriangle(A,B,C)&&E.isInTriangle(A,B,C)) {D.to(E); return ; }  //*:21 show DE when it is in triangle
    if (D.isInTriangle(A,B,C)&&!E.isInTriangle(A,B,C)) { //*:22 if D is in triangle and not E, draw edge from D to exit point
       if (edgesCross(A, B, D, E)) D.to(EE(A,B,D,E));    //*:23 if exit through AB
       if (edgesCross(B, C, D, E)) D.to(EE(B,C,D,E));    //*:24 if exit through BC
       if (edgesCross(C, A, D, E)) D.to(EE(C,A,D,E));    //*:25 if exit through AB
       return ; }  //*:21 show DE when it is in triangle
    if (!D.isInTriangle(A,B,C)&&E.isInTriangle(A,B,C)) { //*:26 if E is in triangle and not D, draw edge from E to exit point
       if (edgesCross(A, B, D, E)) E.to(EE(A,B,D,E));    //*:27 if exit through AB
       if (edgesCross(B, C, D, E)) E.to(EE(B,C,D,E));    //*:28 if exit through BC
       if (edgesCross(C, A, D, E)) E.to(EE(C,A,D,E));    //*:29 if exit through AB
       return ; }  //*:21 show DE when it is in triangle       
    if (edgesCross(A, B, D, E))      //*:16 if hit AB
       if (edgesCross(B, C, D, E)) EE(A,B,D,E).to(EE(B,C,D,E));   //*:17 if also hit BC draw line between the two intersections
       else EE(A,B,D,E).to(EE(C,A,D,E));  //*:18 Assume hits CA, since we must exit triangle entered through AB
    else //*:19 do not hit AB
       if (edgesCross(B, C, D, E)) EE(B,C,D,E).to(EE(C,A,D,E));     //*:20 if hit BC, must also hit DE
    } //*:10

pt EE(pt A, pt B, pt C, pt D) { //*:11  returns intersection point between two edges (Assuming it exists)
    //*:12 Deleted test, which I will do before calling this
    vec T=V(A,B);                      // make vector T=AB
    vec N = R(V(C,D));                 // makes vector N by rotating CD by 90 degrees 
    vec AC = V(A,C);
    float t = dot(AC,N) / dot(T,N);    // compute intersection parameter
    return S(A,t,T);                   //*:13 return point of intersection. S() computes a point on a line (see TAB geo2D)
   }
  
boolean ordered(pt A, pt B, pt C) {return (0<dot(V(A,B),V(A,C))) && (dot(V(A,B),V(A,C))<dot(V(A,C),V(A,C))); }  // tests whether B falls between A and C
boolean edgesCross(pt A, pt B, pt C, pt D) {return (dot(U(R(V(A,B))),V(A,C))>0 != dot(U(R(V(A,B))),V(A,D))>0) // tests whether two edges cross
                                                && (dot(U(R(V(C,D))),V(C,A))>0 != dot(U(R(V(C,D))),V(C,B))>0) ; }

void showEdgeTirangleBorderIntersection(pt A, pt B, pt C, pt D, pt E) { //*:31 show intersection between triangleBorder(A,B,C) and edge(D,E)
   pt XX[] = new pt [4];       //*:32 COPIED (from the code provided at http://www.gvu.gatech.edu/~jarek/3451/projects/P02/)
   int r;                      //*:33 nunber of intersection points between DE and an edge of triangle
   r = ee(A,B,D,E,2,XX);       //*:34 COPIED
   if (r==2) XX[0].to(XX[1]);  //*:35 COPIED
     else if(r==1) show(XX[0]);//*:41 in case DE touches AB at a vertex, show the contact point
   r = ee(B,C,D,E,2,XX);       //*:37 COPIED
   if (r==2) XX[0].to(XX[1]);  //*:38 COPIED
     else if(r==1) show(XX[0]);//*:42 in case DE touches BC at a vertex, show the contact point
   r = ee(C,A,D,E,2,XX);       //*:39 COPIED
   if (r==2) XX[0].to(XX[1]);  //*:40 COPIED
     else if(r==1) show(XX[0]);//*:43 in case DE touches CA at a vertex, show the contact point
  } //*:31

int ee(pt A, pt B, pt C, pt D, float e, pt X[]) { //*:36 (COPIED) returns number of vertices in X[] bounding intersection of edge(A,B) and edge(C,D) with tolerance e
  int r=0;
  if ((abs(dot(U(R(V(A,B))),V(A,C)))<e)&&(abs(dot(U(R(V(A,B))),V(A,D)))<e)) {
    if(ordered(A,C,B)) X[r++]=C;
    if(ordered(A,D,B)) X[r++]=D;
    if(ordered(C,A,D)) X[r++]=A;
    if(ordered(C,B,D)) X[r++]=B;
     }
  else  if ((abs(dot(U(R(V(A,B))),V(A,C)))<e) && (ordered(A,C,B))) X[r++]=C;
  else  if ((abs(dot(U(R(V(A,B))),V(A,D)))<e) && (ordered(A,D,B))) X[r++]=D;
  else  if ((abs(dot(U(R(V(C,D))),V(C,A)))<e) && (ordered(C,A,D))) X[r++]=A;
  else  if ((abs(dot(U(R(V(C,D))),V(C,B)))<e) && (ordered(C,B,D))) X[r++]=B;
  else if (edgesCross(A, B, C, D)) {
    vec T=V(A,B);                      // make vector T=AB
    vec N = R(U(V(C,D)));               // makes unit vector N by normalizing CD and then rotating it by 90 degrees                      
    vec AC = V(A,C);
    float t = dot(AC,N) / dot(T,N); 
    X[r++] = S(A,t,T);  
    }
  return r;
  }