Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!tut.cis.ohio-state.edu!pt.cs.cmu.edu!andrew.cmu.edu!ba0k+
From: ba0k+@andrew.cmu.edu (Brian Patrick Arnold)
Newsgroups: comp.sys.mac.hypercard
Subject: Re: arrowheads at the end of lines.
Message-ID: <oZTNByq00Uh781LrZ6@andrew.cmu.edu>
Date: 6 Dec 89 22:32:30 GMT
References: <QZSVM7u00WB60VEUVB@andrew.cmu.edu>
Organization: Mechanical Engineering, Carnegie Mellon, Pittsburgh, PA
Lines: 93
In-Reply-To: <QZSVM7u00WB60VEUVB@andrew.cmu.edu>


Hello there,

I've spent some time developing influence diagrams to represent variable
dependencies of math eqns in HyperCard.  The key to drawing arrow heads
at any angle is to use the regular polygon tool with polySides set to 3.

Redrawing links presents a bit of a speed problem.  We have a solution
for redrawing links when nodes are moved, but we are not satisfied with
the performance and plan to write a MacApp-based compiled version.

Here is an example of how we draw a directed link between two buttons.

You need to have the following paint globals set:

  set pattern to 12 --  color arrow head black
  set filled to true -- for a solid arrow head
  set polysides to 3 -- arrow heads have 3 sides

You should set these globals in a handler that saves the old values so
that a complementary handler can restore the old values when through -
you also need to "choose browse tool" when through. You should write
SetDrawMode and RestoreDrawMode handlers as your needs require.

--------------------------------------------
ON DoDrawLink fromLinkName, toLinkName
  -- example for two buttons named fromLinkName and toLinkName

  SetDrawMode
  DrawALink the loc of cd btn fromLinkName, <option-return>
    the loc of cd btn toLinkName, <option-return>
    the width of cd btn toLinkName && the height of cd btn toLinkName
  RestoreDrawMode

END DoDrawLink

ON DrawALink fromLoc,toLoc,toSize
  --
  -- Draw a line from fromLoc to an arrow head flush with the rectangle
  -- toSize located at toLoc.  Side effect: leaves you with line tool.
  --
  -- fromLoc   starting point
  -- toLoc     end point
  -- toSize    "width && height" of a rectangle located at toLoc

  set cursor to busy -- feedback when redrawing

  -- compute angle of the line to be drawn
  put (item 1 of toLoc - item 1 of fromLoc) into delx
  put (item 2 of toLoc - item 2 of fromLoc) into dely
  put atan(dely/delx) into myAngle

  -- fudge a little ??? am I computing something incorrectly?
  IF delx < 0
  THEN add pi to myAngle

  -- scale endpoint (toLoc) to account for toSize rectangle overlap
  IF abs(dely/delx) < ((word 2 of toSize / word 1 of toSize)) THEN
    put (1-(abs(delx)-(word 1 of toSize)/2)/abs(delx)) into factor
  ELSE put (1-(abs(dely)-(word 2 of toSize)/2)/abs(dely)) into factor
  subtract round(delx*factor) from item 1 of toLoc
  subtract round(dely*factor) from item 2 of toLoc

  -- generate inset point for arrow head, "5" is arbitrary
  put toLoc into arrowLoc
  add round(5*cos(myAngle+pi)) to item 1 of arrowLoc
  add round(5*sin(myAngle+pi)) to item 2 of arrowLoc
  
  -- do the drawing
  choose regular polygon tool
  drag from arrowLoc to toLoc  -- should draw a triangle (arrowhead)
  choose line tool
  drag from fromLoc to arrowLoc -- should draw a line
END DrawALink
------------------------------------------------

We have tried to replace the trig (above) with more straightforward
calculations to speed up this algorithm, but this actually slowed things
down a bit.  The first "choose regular polygon tool" call takes a whole
1/2 second, but subsequent choose paint tool calls take almost no time.

When undrawing or erasing links, we use the same algorithm with pattern
set to 1 (white).  Then we use the select tool and select the arrow
space (from fromLoc to toLoc), and DoMenu "Transparent" to turn white
pixels into transparent pixels.  This may have unfavorable side effects.

If this is of any help, please let me know.  I also want to hear more
about anyone's work on directed graphs in HyperCard.

Brian Arnold
Research Programmer
Department of Engineering and Public Policy
Carnegie Mellon University