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Dojo Charting Engine
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=========================================================================
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The Dojo Charting Engine is a (fairly) complex object structure, designed
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to provide as much flexibility as possible in terms of chart construction.
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To this end, the engine details the following structure:
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Chart
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---PlotArea[]
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------Plot[]
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---------Axis (axisX)
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---------Axis (axisY)
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---------Series[]
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A Chart object is the main entity; it is the entire graphic. A Chart may
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have any number of PlotArea objects, which are the basic canvas against
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which data is plotted. A PlotArea may have any number of Plot objects,
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which is a container representing up to 2 axes and any number of series
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to be plotted against those axes; a Series represents a binding against
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two fields from a data source (initial rev, this data source is always of
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type dojo.collections.Store but this will probably change once dojo.data
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is in production).
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The point of this structure is to allow for as much flexibility as possible
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in terms of what kinds of charts can be represented by the engine. The
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current plan is to accomodate up to analytical financial charts, which tend
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to have 3 plot areas and any number of different types of axes on each one.
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The main exception to this is the pie chart, which will have it's own
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custom codebase. Also, 3D charts are not accounted for at this time,
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although the only thing that will probably need to be altered to make
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that work would be Plot and Series (to accomodate the additional Z axis).
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Finally, a Plot will render its series[] through the use of Plotters, which
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are custom methods to render specific types of charts.
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-------------------------------------------------------------------------
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In terms of widgets, the basic concept is that there is a central, super-
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flexible Chart widget (Chart, oddly enough), and then any number of preset
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chart type widgets, that are basically built to serve a simple, easy
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purpose. For instance, if someone just needs to plot a series of lines,
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they would be better off using the LineChart widget; but if someone needed
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to plot a combo chart, that has 2 Y Axes (one linear, one log) against the
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same X Axis, using lines and areas, then they will want to use a Chart widget.
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Note also that unlike other widgets, the Charting engine *can* be called
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directly from script *without* the need for the actual widget engine to be
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loaded; the Chart widgets are thin wrappers around the charting engine.
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