v1.5.6 how to add XYLineAnnotation?

[matoos32]

In response to jfree/jfreechart#197 (comment)

@jcobb88 wrote:

@matoos32 Like your library very much. Your API allows to add simply annotations, but how do you add something like XYLineAnnotation, which require two x and y values? Adding those directly to the XYPlot obviously doesn't work when we disable gaps. If not possible, what would be a workaround?

@jcobb88 thanks for your kind feedback. Happy it's been useful.

I examined the XYAnnotation type hierarchy and I see each implementing class has a different constructor. IXYAnnotationBuilder was quickly coded around XYPointerAnnotation without assessing all of the jfreechart annotation classes. So IXYAnnotationBuilder will likely need additional methods to suit all the XYAnnotation implementations, but that doesn't scale well and will get ugly. So it needs some thought. I'll create a project to support all annotation types.

In the mean time I found you can add the XYLineAnnotation to the disabled-gap chart using the integer indices of desired date-axis points. See the snippet below to further decorate the built chart.

Inserting new charts in the demo project JFreeChartBuilderDemo:

    JFreeChart chart = getDailyStockChartBuilder().title("XYLineAnnotation Example With Time Gaps").build();
    CombinedDomainXYPlot combinedPlot = (CombinedDomainXYPlot) chart.getPlot();
    @SuppressWarnings("unchecked")
    List<XYPlot> subplots = combinedPlot.getSubplots();
    XYPlot firstPlot = subplots.stream().findFirst().get();
    long[] timeArray = dohlcv.dates();
    final int index1 = timeArray.length - 10;
    final int index2 = index1 + 5;
    final long date1 = timeArray[index1];
    final long date2 = timeArray[index2];
    final double price1 = dohlcv.highs()[index1];
    final double price2 = dohlcv.highs()[index2];
    firstPlot.addAnnotation(new XYLineAnnotation(date1, price1, date2, price2, BuilderConstants.DASHED_LINE, Color.MAGENTA));
    
    charts.add(chart);
    
    JFreeChart chart2 = getDailyStockChartBuilder().title("XYLineAnnotation Example NO Time Gaps").showTimeGaps(false).build();
    CombinedDomainXYPlot combinedPlot2 = (CombinedDomainXYPlot) chart2.getPlot();
    @SuppressWarnings("unchecked")
    List<XYPlot> subplots2 = combinedPlot2.getSubplots();
    firstPlot = subplots2.stream().findFirst().get();
    final int plot2Index1 = timeArray.length - ohlcStartIndex - 10;
    final int plot2Index2 = plot2Index1 + 5;
    firstPlot.addAnnotation(new XYLineAnnotation(plot2Index1, price1, plot2Index2, price2, BuilderConstants.DASHED_LINE, Color.MAGENTA));
    
    charts.add(chart2);

[matoos32]

Now planned and tracked in this project: https://github.com/users/matoos32/projects/1

[matoos32]

@jcobb88 I added a builder for XYLineAnnotation.

It's in the develop branch as of pull request #58.

There's an example in the demo app I just migrated in (JFreeChartBuilderDemo.java#L304)

Give it a go and let me know what you think!

[jcobb88]

@matoos32 Looks good, thanks! As you know I suggested also some other ideas.
I did a lot of workarounds by getting the specific XYPlots and replacing/adding the annotations. So that works quite well. Some things are a little less clear, e.g. changing the tick labels, so if your time is restricted you may focus on those things and add the workaround for changing data on the plot: retrieving subplots and adding annotations directly (using indices for gapless charts).

[matoos32]

@jcobb88 I can look at tick labels next. #53

I'm unclear if you still have an issue with gapless plot annotations not drawn correctly when updating data. If so, could you submit a bug issue showing how to reproduce it?