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diff --git a/design/enhancements/multiple_axis.txt b/design/enhancements/multiple_axis.txt new file mode 100644 index 0000000..66fcf99 --- /dev/null +++ b/design/enhancements/multiple_axis.txt @@ -0,0 +1,97 @@ +eZ component: Graph: Multiple axis, Design +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +:Author: $Author$ +:Revision: $Revision$ +:Date: $Date$ + +Introduction +============ + +Description +----------- + +Multiple axis are used in three different cases. + +- In stock chart, for example, they are used to show a different meaning of + the displayed data, for example the value of a single stock option and the + value sum of the complete company. + +- Another case multiple axis may be used, is displaying relating data in one + chart which has completely different scalings or units, like the used RAM + and the load on a machine. + +- A third case multiple axis could be used for, are named separators to + highlight data borders in your chart. In this case the step labels should be + at least optional. + +Requirements +============ + +From an implementation point of view the feature seperates into two different +APIs we need to define. + +Adding additional axis +^^^^^^^^^^^^^^^^^^^^^^ + +When adding additional axis we want to support a finite number of marker axis, +at every possible position in the chart. + +:: + + $marker = new ezcGraphChartElementLabeledAxis(); + $marker->position = ezcGraph::LEFT; + $marker->chartPosition = .4; + + $chart->additionalAxis[] = $marker; + +The property $position is already used by ezcGraphChartElement to indicate the +overall position and accepts bitmasks of LEFT, RIGHT, BOTTOM and TOP. For Axis +this indicates the base point of the axis and for additional axis it will +define wheather the new axis is an X or Y axis in the cartesian coordinate +system of bar and line charts. + +As the property $position is already used the property $chartPosition +indicates the position of the axis in the charts data section. A value of 1 +will place the axis at the very end, and a value of 0 at the very beginning of +the data. + +In the example above ezcGraph::LEFT means that the axis is drawn from the left +to the right, so it is an additional x axis, and the $chartPosition indicates +the position at 40% of the chart data bounding height. + +Adding data for additional axis +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Data may be added explicitely on one of the additional axis to use different +scaling und units for this dataset. The axis values are received from the data +sets when rendering the charts, so that we are able to define the usage of an +additional axis at any point before rendering. + +:: + + $chart->data['foo'] = new ezcGraphArrayDataSet( ... ); + $chart->data['foo']->xAxis = $marker; // See last example + $chart->data['foo']->yAxis = $chart->yAxis; // Redundant + +The assignement of additional axis is optional and if none was defined the +original common chart axis will be used. You may define custom axis for one or +both axis. + +Special consideration +===================== + +You may of course define custom scaling, custom axis types and custom axis +label rendering algorithms for each of the used axis. + +If no data set has been assigned to a axis it will not render any labels by +using the ezcGraphAxisNoLabelRenderer. Otherwise the assigned data will be +used the common way to calculate some default step sizes. + + +.. + Local Variables: + mode: rst + fill-column: 79 + End: + vim: et syn=rst tw=79 |
