Friday, February 2, 2018

Friday Fun LIX - Parallel Coordinates Chart

Aloha from Singapore one more time,

Today I have a chart for you which was a bit tricky to implement. It's a so called parallel coordinates chart and to be honest it doesn't look really fancy at a glance but it is really neat.
If you have no idea what it looks like here is a little image that show one...

First it looks like some kind of simple line chart but it's not. With this chart one can compare objects in a nice way. So let's assume you would like to compare cars and you would not only to compare one property of the cars like horsepower but a set of properties (e.g. cylinder, horsepower, acceleration, weight, consumption, etc.) and the whole comparison should be in one chart.
In this case the parallel coordinates chart ist perfect. Here is a little screenshot of my implementation that uses this example...

In this chart each line represents one car (e.g. the blue line represents my Smart Roadster Coupé and the purple line represents the Bugatti Veyron...a fair comparison right ;) ).
Now the interesting part about that chart is that it makes it easy to find similarities between cars or that you can figure out trends easily.
There are tons of possibilities on how to extend this chart but because I do not have the time for that I've just added two things that I've found very nice:

  • Dragging axes
  • Filter specific lines

So you can imagine that the order of the categories has a big impact on the expressiveness of the chart and therefor it is possible to drag a category by dragging the header of a category to another position...

Here I've simply moved some categories around to show the effect of the different category order.
The filtering of specific lines (cars in this example) works similar. Here you simply click close to one axis and drag down and you will see that a little rectangle will be drawn that selects the lines in the range of the rectangle.
If you release the mouse button it will show you something similar like follows...

As soon as you select some lines all other "unselected" lines will be drawn in light gray (configurable) and the selected lines will be drawn in blue (configurable). In addition the names of the selected lines will be shown on the left side. 
Once you click again somewhere the selection will be removed again.
In principle that's it and I hope it might be useful for someone. As always I have no usage for it at all :)
The chart is part of my JavaFX charts library where the current version is 1.0.5 and that you can found here:

Source at github

Binaries at bintray or Maven Central

And if you would like to see it in action, here is a short screen video that I've recorded...

That's it for today, so enjoy Carnival and don't forget...keep coding... ;)

Friday, January 26, 2018

Friday Fun LVIII - Some more charts...

Aloha from Singapore again,

Today I finally managed to create some little Friday Fun components for you, so today I have two new charts for you that are part of my JavaFX charts library.
The first chart is a ConcentricRingChart that looks as follows:

Nothing really special but fun. You have a set of ChartItems that you pass to the ConcentricRingChart. The values are always normalized so that the current maximum value fills up to 100%. You can choose between different NumberFormats for the value in the bar and if you click with the mouse on a bar a little popup will show you some information on the clicked item.
In addition you can also sort the bars ascending and descending if you like and of course animation is also available. If you would like to see it in you go...

The other chart that I've created is similar which is the reason why I have two components today. This one is a ComparisonRingChart where you can compare two series of ChartItems. The first series will be shown on the upper part and the second series on the lower part. It looks like this...

The upper series goes from left to right where the lower series will be visualized from right to left. Everything else is exactly the same as in the ConcentricRingChart, meaning to say you also have the mouse interaction and the popup.
And again if you are interested in how it looks in you are...

As already mentioned both components are part of my little JavaFX charts library that you can found here...

Source Code: github

Binaries: bintray and Maven Central 

And that's it for today...cheers from Singapore and keep coding... ;)

Friday, January 12, 2018

Friday Fun LVII - Stream Charts


Here we go again...last week I stumbled upon a really nice charts that are inspired by Edward Tufte's Stream Charts. This is how they look like...

And here you can find more information about them.
The chart can be used to visualize a series of data with the variation of the data it contains over time. On each date different items of the series are stacked like in a stacked bar chart. The items are sorted by their value from bottom to top, meaning to say the items with the lowest value are always at the bottom and the one with the highest values are always on top.
To be honest I have again no use case for it but I really like the visualization. By choosing the colors wisely one could visualize dominating series over time very well.
Long story is my implementation of such a chart...

As you can see I don't have such good data as in the example above but you get the idea :)

To create such a chart I make use of my ChartItem class which has a timestamp property that is needed here to group the chart items for the visualization. The idea is to have a list of ChartItems that may also contain multiple ChartItems from the same day. The StreamChart component has a category property which can be one of the following categories:

  • DAY
  • WEEK
  • YEAR

So let's assume you have a list of ChartItems that contains data from different days and you would like to visualize the chart grouped by days you set the category to DAY.
With this feature you can define if you would like to group the given list of ChartItems by one of the above categories...hmm...hope that explanation was more or less clear :)

It might be easier to simply take a look at the source code (see links below).

In principle this chart is similar to the Sankey Plot but not exactly the same so I've started from there and created a modified version which you can see above. This chart is now part of my own JavaFX charts library which you can find here:

sources at github

binaries at bintray

Please find the demo classes for all the charts in the test package.

Well that's it for keep coding...

Friday, January 5, 2018

Friday Fun LVI - Nested Bar Charts

Aloha and a happy new year,

Today I just have a short post about some nice little bar chart which I've found last week when looking for new ideas on the web. Here is the image I've stumbled upon...

I saw it and directly understood the idea behind it because it's like a compact view of two bar charts. The big bars in the background show the sum of all inner bars (like in a stacked bar chart) and the inner bars visualize the distribution of that sum into portions. If you want to know how to realize this kind of chart in Excel you should take a look at Jon Peltier's blog where this image was taken from.

To be honest the thing that got my attention are the colors he used for this chart because they directly reminded me on the Material Design colors
And because I once implemented these colors in JavaFX I gave it a try.
Well I was surprised how easy it was to implement and finished the whole thing within 1.5h and here is a little screenshot of the result...

As you can see this kind of chart works really well with the Material Design colors. So it does not make sense to use it for everything but there might be some use cases where saves a lot of space and still transfers the information.

Because I will add this chart to my JavaFX charts library anyway I did not spend more time on implementing axis and labels but I only implemented a mouse event handler. Meaning to say if you click on an element the component will fire an event that contains the data of the selected series (the big bar) and if you've clicked on one of the inner bars it will also contain the data of the selected item.
Using this event I've implemented a simple popup that will show the selected data.

This kind of chart can for example be used to compare sales data of products per quarter or similar things, you will find something ;)

As always the source is available over at github so enjoy playing around with it.

That's it for today...I wish you a codeful year 2018...keep coding...

Friday, December 29, 2017

Friday Fun LV - Florence Nightingale inspired Coxcomb Chart


For the last Friday in 2017 I have another friday fun component for you. It's a variation of a donut chart where the segment width varies with the value. To give you an idea what this chart looks like here is a little picture that I've found on the web...

In principle this chart is not really fancy but the one thing that caught my attention are the shadows that are only visible on the lower elements, meaning to say they are not besides the segment. In JavaFX we have effects like drop shadows directly build in but they won't work here because if you would use a simple drop shadow on each segment you would get something like follows...

So we now have the drop shadows but not only on the lower segments but all around each segment which is not the same. One trick could be to use clipping for which you have to clip each segment with a path.
Well to be honest I was to lazy and decided to go another way. In principle you could imitate a drop shadow by using a linear gradient. This works but is not easy to achieve. So what I did was to add another segment at the end of each segment which I stroke with a linear gradient that goes from gray to transparent. To give it a little bit more realistic look I've also added a gaussian blur. So my result looks as follows...

To be honest I'm not really satisfied with the result because the shadow still looks not realistic enough but hey...for an early morning hack it's good enough ;)

Well what I should I say...this shadow problem nagged me last night so I reworked my implementation and now I make use of the inbuild DropShadow effect in combination with clipping. On the following picture you can see the LinearGradient based approach (left) compared to the DropShadow approach (right)...

To make the effect more visible I've set the drop shadow color to opaque black on the right side and now the shadows look more least to me ;)
For the new approach I've added an additional path at the end of each segment and adjusted the shadow offset in x- and y-direction for each segment.
This worked nicely except the fact that the shadow also showed up outside of the segment.
Well a picture is better than thousand words, so on the following picture I've used plain red for the drop shadow color and here you can see what I'm talking about...

To avoid this problem I simply clip each segment with a circle that has the same radius and by using this little clipping trick the result looks like follows (with black as shadow color again)...

And now it looks exactly as I would like to see it :)
To use the clipping in JavaFX Canvas (or HTML5 Canvas) you have to define a path that will be used for the clipping and call clip() before you draw the elements that you would like to clip. The next thing you need to keep in mind is that once the clipping path is set it will affect all operations defined here.
In my case the problem is that the radius of the segments will increase so the clipping path also has to "grow". The canvas has a nice feature which makes it possible to save and restore it's state. Meaning to say before I set the clipping path I save the canvas by calling the save() method on the GraphicsContext and after I've finished the segment I reset the canvas to the saved state by calling the restore() method on the GraphicsContext. The nice thing is that you can save/restore the canvas as often as you like...but you have to keep track of it.

As a little advice let me tell you that if you use save/restore more than once it makes sense to either add some comments to each save/restore statement so that you know for which operation you save/restore or you also simply intend your code after each save statement to visualize the saved code blocks.

But now back to the chart...
For my implementation of the coxcomb chart the values of each segment are not related to the segment radius and therefor it only makes sense if you sort the items in the list.
For this reason I've added two convenience methods to sort the chart either ascending or descending where ascending would look like this...

Well I like the descending version more but this is personal taste.
I did not add a legend to the chart because I think this could be a separate control to be more flexible. I've created a simple item class that has properties for value, name and color.
To create the chart above you simply need the following code...

Item[] items = {
    new Item(27, Color.web("#96AA3B")),
    new Item(24, Color.web("#29A783")),
    new Item(16, Color.web("#098AA9")),
    new Item(15, Color.web("#62386F")),
    new Item(13, Color.web("#89447B")),
    new Item(5, Color.web("#EF5780"))
CoxcombChart chart = new CoxcombChart(items);

I'm always impressed how easy it is to create stuff like this in JavaFX, creating the control and writing this blog post tooks me only 2.5h which is one of the reasons why I love coding in JavaFX, the time from the first idea to some running code is really short and with this the productivity is really high and the code for the control is just around 280 330 (I've added 2 properties with their getters and setters) lines incl. import statements, license etc. Long story short...I ❤️ it :)

Oh and if you are interested in the code you can find it as always on github.

This chart is very specific and does not work for everything but it could be quite useful for some special use cases and to be honest it simply looks nice :)

So I guess that's it for 2017, now I wish all of you a happy new year and...keep coding...

Friday, December 15, 2017

Friday Fun LIV - Path Gradient


I've always thought about how to implement a path gradient. Meaning to say a gradient that follows a path. First of all keep in mind that this kind of gradient is not used very often but sometimes it can create some really nice effects.
I've mainly saw the effect in circular components like the fitness gauge on the Apple Watch...

The color of each bar changes along the bar as you can see on the image. For this specific problem I've created the ConicalGradient in the past which works nicely for circular components but what about this...

If you would like to fill the path above with a gradient from blue over green and yellow to red you will see that it won't work with linear gradients. You can either fill it horizontally or vertically but both times the gradient won't follow the path itself. So here are two examples...

To fill it with a gradient along the path you need to split the path into small segments and fill each segment with a linear gradient along the line.
If you go with this approach you can achieve something like follows...

As you can see here it works nicely but that was not that easy to realize. The most important part of this little fun project was taking a closer look to the goodies that are already in the JDK. Especially the Java2D package contains a lot of nice stuff.
So my idea was to use this kind of path gradient in the JavaFX canvas node and lucky me the Java2D api is quite close to the JavaFX canvas api.
I won't go through the code because it's simply to much but let me explain the steps that are needed to achieve that result...

  • Split the path into it's elements (MoveTo, LineTo, QuadCurveTo, BezierCurveTo, Close etc.)
  • Split each element into single lines
  • Stroke each single line with the right part of the complete gradient
Like already mentioned above a lot of the functionality is already in the JDK but unfortunately it sometimes is hidden in private classes that are not accessible from the outside. So the solution for this problem was to fork all parts that I needed from the Apache Harmony project (the stuff Android is based on). So in principle I've forked the all classes from the Java2D packages that are related to bounds, shapes and transforms.
In the classes above I've removed all 3D related things and completely switched to doubles instead of floats.
I've also added several other classes and added functionality to some of the classes. One problem was for example that in the JDK there was no code to split lines into "sub-lines" which means I had to add this kind of things.
I've also renamed some classes to be more compatible to the JavaFX canvas. So the CubicCurve now is a BezierCurve etc.
In the end I've needed a path class that holds all elements and a lookup mechanism for the gradient.
Long story short with my current implementation the code to produce the path gradient will look like follows...

GradientLookup gradientLookup = new GradientLookup();
gradientLookup.setStops(new Stop(0.0, Color.BLUE),
                        new Stop(0.25, Color.LIME),
                        new Stop(0.5, Color.YELLOW),
                        new Stop(0.75, Color.ORANGE),
                        new Stop(1.0, Color.RED));

Path path = new Path();
path.moveTo(91, 36);
path.lineTo(182, 124);
path.bezierCurveTo(248, 191, 92, 214, 92, 214);
path.bezierCurveTo(-26, 248, 200, 323, 200, 323);
path.bezierCurveTo(303, 355, 383, 141, 383, 141);

double lineWidth = 20;

Canvas            canvas = new Canvas(400, 400);
GraphicsContext2D ctx    = canvas.getGraphicsContext2D();
PathGradient.strokePathWithGradient(ctx, path, gradientLookup, lineWidth, StrokeLineCap.ROUND);

So as you can see I've tried to keep the api as close to the JavaFX canvas api as possible but instead of drawing the path directly on the canvas context you first create the path object, define a gradient lookup which contains the list of stops and colors you need for the gradient and define width for the stroked line.

That's already neat but it could even be better because in the Path class you will find a SVGParser and with this you can directly use a SVG path string from an SVG file.
As an example here is the SVG file of the path on the above image...

<?xml version="1.0" standalone="no"?>

<!-- Generator: Adobe Fireworks CS6, Export SVG Extension by Aaron Beall ( . Version: 0.6.1  -->
<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "">
<svg id="Untitled-Page%201" viewBox="0 0 500 500" style="background-color:#ffffff00" 
    xmlns:xlink="" xml:space="preserve"
    x="0px" y="0px" width="500px" height="500px">
    <path d="M 91 36 L 182 124 C 248 191 92 214 92 214 C -26 248 200 323 200 323 C 303 355 383 141 383 141 " stroke="#000000" stroke-width="1" fill="none"/>

And with the the mentioned parser the code above could also be written like follows...

Path path = new Path();
path.appendSVGPath("M 91 36 L 182 124 C 248 191 92 214 92 214 " +
                   "C -26 248 200 323 200 323 C 303 355 383 141 383 141");

double lineWidth = 20;

Canvas canvas       = new Canvas(400, 400);
GraphicsContext ctx = canvas.getGraphicsContext2D();

PathGradient.strokePathWithGradient(ctx, path, gradientLookup, lineWidth, StrokeLineCap.ROUND);

To me that looks quite ok :)
As always I do not really have any use case yet so the whole thing is not tested for all possible use cases but at least it will give you an idea what is possible :)

And also as always the code is available on github.

Well that's it for today...I hope it was somehow interesting...keep coding... :)

Wednesday, December 6, 2017

William Playfair inspired charts...


Today I just would like to share a little blogpost about a chart that I've implemented last Friday evening. The chart design is inspired by William Playfair who invented this kind of chart to visualize economic data like import and export of theUS in relation to other countries.
One of his charts looks like follows...

The idea is pretty simple, take two line charts and fill the area between the two charts with a color. The color depends on which line is on top. With this technique one can visualize for example gain and loss of processes etc.
Like mentioned the idea is simple but the realization is not as trivial as it looks. The problem here is that you have two separate line charts that you have to combine to not only one polygon but to multiple polygons.
So every time the two lines cross each other one has to fill the area before the intersection point with one color and the area after the intersection point with the other color.
After thinking about the chart for a bit I've got an idea on how to realize that behavior and here is one result...

As always I do not really have a use case for that chart but I can imagine that it might be useful for someone out there :)

So if you would like to play around with it, feel free to check out the code at github.

I hope to find some time within the next days to add some interactivity to the stay tuned :)

Well...I guess that's it for keep coding... :)