On 30/10/2020 22:40, Roger Guay via use-livecode wrote:
Let’s try this again after spellchecking:

Yes, yours is a good example of a bifurcated line. But now imagine producing 
this line programmatically with an equation that:

Produces a constant y value of 149 as x progresses from 35 to 235 (no problem)
Then produces 2 different but simultaneous values of y as x progresses from 235 
to 335. This is the problem as you don’t want the end point of the separated 
lines to connect. If you place an empty line in the points after each iteration 
beyond x = 235 then you end up with the bifurcated lines being points rather 
than a solid line.

How do plotting programs handle this situation????

Here are two different ways you could do it.

1. simple - assume there would (could) be two Y values for any x, and just calculate two series, and combine them for output.

2. harder - for each x value, keep track of the previous y value for each series, and if necessary, put in a 'skip' plus new value plus skip ...

NB makes for a more complex polygon; each new x value after bifurcation results in 5 lines added to the points.

on mouseup
   local tSeries1, tSeries2, thepoints
   if the shiftkey is down then

      -- the easy way - just allow for the possibility of two series of points all along
      repeat with i = 35 to 335
         -- calculate series 1
         if i < 235 then
            put i,249 &CR after tSeries1
            put i, 249+(i-235) &CR after tSeries1
         end if
         -- calculate series 2
         if i < 235 then
            -- do nothing - it's the same as series 1
            put i, 249+2*(i-235) &CR after tSeries2
         end if
      end repeat

      put tSeries1 &CR & tSeries2 into thePoints
      set the points of grc "X" to thePoints
      set the foregroundColor of grc "X" to "blue"
      -- the harder way - multiple series ...
      -- does each step for each series ... much more complex polygon, but ...
      local t1, t2, tLast1, tLast2
      repeat with i = 35 to 335
         -- calculate values
         if i < 235 then
            put 249 into t1
            put 249 into t2
            put 249+(i-235) into t1
            put 249+2*(i-235) into t2
         end if
         -- put in series 1
         if tLast1 is not empty then
            put i-1, tLast1 &CR & i, t1 &CR after thePoints
         end if
         -- possibly put in series 2
         if tLast1 <> tLast2 OR t1 <> t2 then
            put CR after thePoints -- blank skip over to series 2 value
            put i-1, tLast2 &CR & i, t2 &CR after thePoints
            put CR after thePoints -- blank skip back to series 1
         end if
         put t1 into tLast1
         put t2 into tLast2
      end repeat
      set the points of grc "X" to thePoints
      set the foregroundColor of grc "X" to "red"
   end if

end mouseup

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