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  • Friday Fun LIV – Path Gradient

    December 15th, 2017


    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…

    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…

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

    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… 🙂

    William Playfair inspired charts…

    December 6th, 2017


    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 chart…so stay tuned 🙂

    Well…I guess that’s it for today…so keep coding… 🙂

    Friday Fun LIII – Sankey Plots

    December 1st, 2017

    Aloha everyone,

    Creating charts is really fun…again Thomas Nield(@thomasnield9272) pointed me to a nice chart which is called Sankey chart and again I could not withstand to try my best to implement it in JavaFX.

    To give you an idea on what I’m talking about here is an example of such a Sankey plot…

    Compared to last weeks Circular plots these plots can be multilevel and after searching the web for some hours I figured out that you can find all sorts of Sankey plots which might look completely different…here another example…

    That doesn’t make it easier to implement such a chart and so I’ve started reading about the history of that chart. In the end it turned out that the main purpose of this kind of chart is the visualization of flows where the width of the arrows/lines is shown proportionally to the flow quantity.

    So I had to make a decision which style I should follow and I’ve decided to go with the first visualization of the above pictures. Lucky me there is also a version of the Sankey plots in the Google charts which I took as a template. Here is a screenshot of what I’ve come with…

    This is the more colorful version of the chart but it is also possible to create other versions as you can see here…

    In this version I’ve used different parameters for the width of the items and here also the direction of the flow is indicated by arrows (but I only support one direction anyway).

    To get nice results you have to keep in mind that in my implementation you have to think about how to order the items in the chart when adding it to the control.
    Meaning to say I do not have some hyper smart algorithm that do some fancy automatic sorting of items but you have to use your own brain and think about the chart before you create it. For the example above I’ve added the items exactly in the order as they appear on the chart which would look like follows…

    After that is done you have to define the connections between the items by defining only the outgoing streams for each item. Because that’s a lot for the chart above I will only show you the ones for the first column which will look as follows…

    As mentioned you define the streams that goes from each item to other items with their values.
    After that is done you can setup the chart using the SankeyPlotBuilder as follows…

    And that’s all it takes to create such a chart. Because the chart is again based on the JavaFX Canvas node there is no interactivity at the moment but I’m already working on a little project that will make it possible to have interactivity in the future…so stay tuned 🙂

    Of course the code is available on github as always.

    That’s it for today…so keep coding…

    Friday Fun LII – Circular Plots

    November 24th, 2017


    Slowly getting into the charting business 😉

    After Thomas Nield (@thomasnield9272) pointed me to so called Circular Plots I’ve couldn’t hold back. If you know these charts you might understand why I was so keen on creating such a chart.

    So to give you an example here is an image of such a chart…

    To be honest when I first saw the plot I was fascinated even without knowing how to read it and without knowing what this chart is good for. But after I took a look at more and more of those charts I got an idea on how to use them.

    So I’m not a data scientist which is the reason why I’ve implemented it in a way that seemed logical for me.

    The biggest problem was to find some data that I could use for the visualization. So in the end I’ve decided to take the public available data from the current parliamentary election in Germany.
    To give you an idea what my chart is visualizing I think I need to explain it a bit. Each section on the chart shows one party with it’s name, color and the voting result related to the number of eligible voters (61.5 Million).

    Because there was a new party this year it was interesting to see where did the voters came from, so my chart visualizes the migration from all parties to other parties. The bigger the arrow the more voters migrated from the party to another.

    So here is my chart…

    So in the chart one can see that most of the AfD voters came from the Union party, the so called Non-Voters (“Nichtwaehler”) and others.

    I’ve also created another chart that shows fictive data about travellers that travel between some asian countries. As always I do not have any use case for this chart and cannot guarantee that it is useful for real data analysis but at least it works for me and was fun to create. So here is the other chart…

    At the moment there is not interactivity in this chart but if I will find some time I will definitely add it.

    As always you can find the code on github.

    That’s it for today…enjoy the upcoming weekend and…keep coding 😉

    Just some conversion tool…

    November 20th, 2017


    Last week I was in Switzerland and somehow got reminded on some tool that I’ve created some time ago which might be handy for some of you. It is a simple unit conversion tool which supports conversion between the following categories of units:

    • ANGLE
    • AREA
    • DATA
    • ENERGY
    • FORCE
    • LENGTH
    • MASS
    • SPEED
    • TIME
    • TORQUE
    • VOLUME
    • WORK

    As an example let’s convert a temperature in Celsius in Fahrenheit and Kelvin which would
    look as follows:

    So first you create a Converter instance with a category and a base unit (here Temperature as category and Celsius as base unit).

    After that is done you can convert celsius based temperatures to other units like Fahrenheit and Kelvin.

    In addition I’ve also added a method to shorten long numbers with abbreviations.

    Sometimes this is really useful when working with big numbers, a little example would look like follows…

    And the result will look like this…



    The format method will support the following abbreviations

    • kilo
    • Mega
    • Giga
    • Tera
    • Peta
    • Exa
    • Zetta
    • Yotta

    Not really sure if you can use it but at least I wanted to share it with you folks… 🙂

    The code is as always available on github.

    That’s it for today…keep coding…