[Help] Drawing a polyline over a tokens lastmove property

I'm looking for a script that, when called, will draw a polyline along the path of the token's last movement.  (Think TRON lightcycles, your token is the cycle and the script adds the polyline after the token moves(via !api not change:graphic))  What's screwing me up on my own attempt at it is that creating a path uses points relative to the bounding box, whereas the lastmove property uses screen coordinates.  Top,Left of the bounding box is a virtual point that's rarely on the path itself so it has to be derived.  My skill level means I can probably get it working given a few weeks, but I'm hoping the pros here can help me reduce that time (and amount of hair-pulling).   Know of anything like this I can use or look over?

I can probably help you with that later today, but if you want to get a head start on it, this is what you needs to do: for the points on the move find the smallest X and smallest Y (not necessarily from the same point). These become the left and top values.  Create a new list of points by subtracting the minimum X and minimum Y from the X and Y of each point. This translates the move points into the line's bounding box relative coordinate system.  Create the path with the left and top from step 1 and the points from step 2. 

I understand the logic needed to derive the numbers, just don't have the coding background to apply that logic in js very quickly :) I have an array built from obj.get("lastmove").split(","); Then I run it through a loop to turn each point into an integer because it will be on a hex grid where tokens snap to non-integer values.  Probably not necessary buts its easier on the eyes to debug outputs that are 35,35,... rather than 34.45235907,35.01349078,...... This loop also finds the lowest x and y values for the Top and Left of the path object later.   Then I run it through a loop to build the string for the path like so: while(j < Steps) {   var coords;   var a;   var b;   if (j == 0) {     a = Path[j] - TopMin;      b = Path[j+1] - LeftMin;     coords = '[\"M\", ' + a + ', ' + b + ']';   } else {     a = Path[j] - TopMin;     b = Path[j+1] - LeftMin;     coords += ',[\"L\", ' + a + ', ' + b + ']';   }   j+=2; } var coordinates = JSON.stringify([coords]); However coords is outputting as "[\"M\", 0, 0],[\"L\", 70, 140],[\"L\", 210, 140],[\"L\", 210, 70]"  (whether I escape the " with a \ or not in the while loop) so of course JSON.stringify is giving me "[\"[\\\"M\\\", 210, 70],[\\\"L\\\", 140, 70],[\\\"L\\\", 0, 70],[\\\"L\\\", 0, 0]\"]" which is meaningless to the createObj laster on.

Don't make coords a string that you stringify. The purpose of JSON.stringify is to turn a JavaScript object or primitive into a valid JSON string representative of that object/primitive. Which means if you call JSON.stringify([stringValue]), the JSON string you create will be representative of an array with a single string element. Instead of var coords; coords = '[\"M\", ' + a + ', ' + b + ']'; coords += ',["L\", ' + a + ', ' + b + ']'; , try var coords = []; coords.push(['M', a, b]); coords.push(['L', a, b]);  JSON.stringify will do the rest.

Output still looks like: "[[[\"M\",0,210],[\"L\",420,140],[\"L\",420,0]]]" and its creating a blank path.

Okay so if you leave out top, left, width, and height in the createObj call and use actual screen x and y coordinates in the path object it works them out internally.  It works perfectly now. Thanks Aaron and Brian!

Cheers!  Happy Rolling!