Thursday, June 25, 2009

Added Features and getting ready for Beta (Alpha?) Testing

  1) Delete Node
  It is now possible to delete a node in the graph, along with all of its child edges. The main reason for why I was avoiding implementing this was because I still hadn't fixed the problem of multiple root nodes causing the javascript to crash. Once I figured out how to allow for more than one root the repulsive forces caused the disconnected components to push each other all the way to the end of the screen. Eventually I found a solution to the problem. 
  Allowing for the deletion of nodes took some reworking of how I built the graph, particularly extraction from the SQLite database. My method followed the precondition that each index 1 through the number of rows in the database corresponded to an edge, but with nodes being deleting this no longer held. Luckily, this problem didn't take me long to solve. Now I have delete working exceptionally.
  2) SVG Edges, HTML Nodes
  I really wasn't fond of the dotted line appearance that the edges had when made by HTML div tags, so I changed them to SVG. However, this took awhile because I was held back by desperately searching for how to use SVG's image objects or add background images to the SVG shapes. I ended up doing what I was initially trying to avoid - editing the JSViz module even more. I had to alter how the view object was created to use both HTML - for the nodes - and SVG - for the edges. Now the edges are one smooth object and viewing the graph is significantly quicker, since I now longer have to add multiple event listeners for each pixel of the edge.
  3) Direct Graph
  This took me two whole days - two days to put triangular markers on edges pointing in the direction of the relation. My first idea was to brute force the calculations and add a triangular SVG object on top of the edge, with the tip always pointing at the destination of the edge. This involved using the X,Y co ordinates of both the source node and destination node as my only two references to find the equation for the three points, no matter what the position was. So I busted out my geometry, and was I in for a surprise. I hadn't done geometry in a long time. I couldn't even remember how to get the equation of the perpendicular line to a point on a slope - yes, my method required knowing this. Needless to say, after a lot of scribbling formula's and drawing mock graphs what I ended up with was a dozen seizure inducing, constantly moving, polygons that weren't even remotely near where I hoped they would be. I abandoned that idea by mid-afternoon and set out to do research. It turned out that SVG polylines had marker objects which do exactly what I wanted to do, but they were in no way simple to figure out. I still can't figure out why a style property would be called marker-mid when it does not place a marker in the middle of the line, but instead places one at every odd vertex excluding the start and the end. I mean, marker-start and marker-end do what they sound like they do, so this baffled me. Eventually I discovered that an odd combination of editing marker properties to refY = "5" and refX = "-15", in combination with a path obect with d = "M 10 10 0 5 10 0 z" resulted in the arrow positioned where I want. Why does it work? I'm not really sure, except M 10 10 positions the center at (10, 10), 0 5 draws a line from (10, 10) to (0, 5), then 10 0 draws a line from (0, 5) to (10, 0), and z close the object. What these coordinates are relative to, and what refY = "5" and refX = "-15" are relative to is still a mystery to me. 
  4) Renaming 
  Renaming my extension from "url" to "BreadCrumbs" took a lot longer than I thought it would, since I had to edit files that I haven't touched in ages, like the manifest file or install.rdf. I used this time to separate my methods into more Javascript files to group related methods together better. This close inspection of my code allowed me to spot some lines that were unneeded or just generally sloppy. In addition to this I added more comments, gave variables clearer names, and did more work on the CSS.
  5) Brainstorming / Implementing a way to easily convey to the user the order of sites visited
  During my demo on Tuesday Jon Pipitone asked about a way to show the order that sites were visited in. Adding the directed edges was meant to address this, but I realize that if one node has multiple edges out of it the direction of the arrow conveys nothing concerning the order the edges were traversed in. So with some brainstorming I decided to add a sidebar menu which shows an ordered list of the websites, based one their entries into the database. The first one in the list is always the root, and then as you go down the list it gets closer to the most recently logged website. The information displayed is only the website title (with the "- Mozilla Firefox" no longer being recorded) and the date/time that the site was first visited on, while logging. To easier display this information I added an effect to the list so that when the user mouses over any node on the graph the corresponding entry on the sidebar lights up.


  I will continue with this idea by having the list in its own container with a scroll bar, so that you don't have to scroll all the way down and not see the graph. Also, I would like to add an event so that when a node on the graph is clicked the list automatically scrolls to center that entry in the list container.

  That's all in terms of added features, for now. Once I'm satisfied with point #5 I'll be writing up some release notes (I haven't done this before) to prepare for the first round of testing. My goal is to have everything ready for Wednesday, July 1st, then hopefully some grad students and/or students in the lab here, BA2270, would be willing to take some time to play around / find bugs / give suggestions / complain about it!

1 comment:

  1. Hi Brent.
    At the top of this blogpost you mentioned you found a solution to the multiple root nodes problem. I am facing the same problem in Jsviz, such that the repelling forces send all the nodes to the edge of the screen.
    May I know what the solution was? Thanks a lot.
    - Kartik