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Ext GWT Premium Member
(Beta 1) BarSeries Stacked Mode Defect (AreaSeries is OK)
In working with the AreaSeries, I finally realized what is wrong with the BarSeries when using it in stacked mode.
The attached AreaChart.png screen shot shows purchases for five different items by day against a daily budget of $50,000. The budget never changes from day to day and is always $50,000. You will see that the top of the area chart is a perfectly straight as an end-user would expect. In the attached ColumnChart_StackedAreaOK.txt I calculated the budget value for the yField to be $50,0000 minus all items purchased. There is no problem here! Apparently the top of each sprite is calculated relative to the zero point on the vertical axis by accumulating the values of the other yFields lower in the stack.
The attached ColumnChartStacked.png shows the same chart done in a BarSeries using stacked mode. Here the budget of $50,000 appears to change a little (plus or minus) from day to day. This is wrong! In the attached ColumnChart_StackedColumnDefect.txt I calculated the budget value for the yField to be $50,0000 minus all items purchased (same as before). Apparently the top of each sprite is calculated relative to the top of the next lower sprite in the stack. Because a fractional pixel cannot be used, this causes little pixel rounding errors that accumulate.
Please correct the BarSeries in stacked mode feature so that the top of each sprite is calculated relative to the zero point on the vertical axis by accumulating the values of the other yFields lower in the stack (same as the AreaSeries). This will greatly simplify things as opposed to adding a separate BarSeries for each yField to work around this problem.
Hopefully, this is an easy change. It will make BarSeries stacked mode more accurate.