[etoys-dev] graphing and watching enhancements

[Scott Wallace]

I've been working on three somewhat related updates for the new release. The attached zip contains the latest versions of all three, which are expected to be loaded in this order:

numberLines-Richo-sw
	Number lines, which can be used as cuisinaire rods, graph axes, etc.

followingWatcher-sw
	Watchers that behave as if attached to their observees, following them around on the screen

graphPaper-sw
	Adds a graph-paper fill style, with a live editor for tuning its parameters


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A "Graphing" category is added to the Objects tool, offering number lines, graph paper, and a prebuilt cartesian plane.  (There are a few more things I was intending to put in this category, but they're not ready so may not make it out this round.)

For graphing, though an "x-y plane" is provided as an example, I think it's best to encourage kids to build their own cartesian plane:  start with a plain "playfield", or plain "graph" paper, and then drop Horizontal and Vertical axes into the playfield, and configure the axes to have the scale and appearance desired, and use the graph-paper panel to make compatible "graph paper" to use with the axes.

Use any "morph" (object) as plot points -- a small Ellipse or Star works well.

If there are horizontal and vertical axes present in a playfield used as a graph, they define the metric by which cartesian coordinates called "xOnGraph" and "yOnGraph" are reckoned.  Look in the "graphing" category of a Viewer for these.

Shift-click on the cyan "open-viewer" icon of any plot point to get an "attached" watcher showing the current "on graph" coordinates of the object.

A Number Line can be configured using items found at the bottom of its halo menu.  But a much more efficient way to configure a number line is by using its Viewer -- look in the "number line" category.

Any playfield can be given a fill style of "graph paper" from the "fill style" item of its halo menu.  A special "graph paper" property sheet allows you to configure grid spacing, tick-mark and legend spacing, and colors of paper and grid.

CAUTION:  If you change the metrics of a number line used as an axis in a playfield showing graph paper, it can easily happen that the grid of the graph paper and the scale of the axes will become out of synch. The user will need to adjust both the graph-paper and the axes so that they match up well together.

Some of this work is still not 100% percent satisfactory, but in view of the need to freeze and test, I put them out now for your scrutiny and comments, and if Karl, Richo, and/or Bert deems it suitable, perhaps one of you can "resolve" them and push them to the repository...

(all these change-sets have also been posted to the tracker.)

  -- Scott

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