[Pascal] [xEdit] DrawArrowHead procedure for PerkTreeUI

//=========================================================================
// Draw arrow head procedure
procedure Form1.DrawArrowHead(n1, n2: TImage);
var
  halfX, halfY, vecX, vecY, sideAX, sideAY, sideBX, sideBY: integer;
  unitX, unitY, orthX, orthY, backX, backY, mag: real;
begin
  // get the vector from one node to the next
  vecX := n2.Left - n1.Left;
  vecY := n2.Top - n1.Top;
  // calculate magnitude of the vector and use it to get a unit vector
  mag := sqrt(vecX*vecX + vecY*vecY);
  unitX := vecX/mag;
  unitY := vecY/mag;
  // get a point halfway between the nodes, and moved up half the length of
  // the arrowhead so the arrowhead is centered
  halfX := ((n1.Left - 5) + (n2.Left - 5))/2 + aHeadLength*unitX*0.5;
  halfY := ((n1.Top - 5) + (n2.Top - 5))/2 + aHeadLength*unitY*0.5;
  // get a vector orthogonal to the unit vector
  orthX := -unitY;
  orthY := unitX;
  // move back from the halfway point a distance equal to the arrow head length
  backX := halfX - aHeadLength*unitX;
  backY := halfY - aHeadLength*unitY;
  // move orthogonally (sideways) a distance equal to the arrow head width
  // we calculate "sideA" and "sideB" for both sides of the arrow head / and \
  sideAX := backX + orthX*aHeadWidth;
  sideAY := backY + orthY*aHeadWidth;
  sideBX := backX - orthX*aHeadWidth;
  sideBY := backY - orthY*aHeadWidth;
  // draw the arrowhead lines
  Image2.Canvas.MoveTo(halfX, halfY);
  Image2.Canvas.LineTo(sideAX, sideAY);
  Image2.Canvas.MoveTo(halfX, halfY);
  Image2.Canvas.LineTo(sideBX, sideBY);
end;